# Effect of Enhanced Nutrition on Mule Deer Population Rate of Change

ArticleinWildlife Monographs 172(1):1 - 28 · December 2010with 245 Reads
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Abstract
• ... Ungulate fawn survival is typically low and variable, consequently annual variation in survival and recruitment of this age class can strongly influence population dynamics (Gaillard et al. 1998(Gaillard et al. , 2000Forrester and Wittmer 2013). Yet, few studies have examined mule deer fawn survival even though this period may be when most mortality occurs in the species (Pojar and Bowden 2004, Bishop et al. 2009, Hurley et al. 2011. ...
... We defined detection probability as the probability that a radio-collared fawn was detected in an alive or mortality state during each monitoring survey. We modeled mortality probability as a function of winter range development, summer range development, adult female, fawn birth, and temporal covariates that we predicted would influence mule deer fawn mortality based on previous mule deer studies (Pojar and Bowden 2004, Bishop et al. 2009, Hurley et al. 2011. Winter and summer range development covariates included the mean distance (km) from the centroid of an adult female's core area to the nearest drilling well pad, producing well pad (http:// cogcc.state.co.us), or road. ...
... Adult female-specific covariates included rump fat thickness (mm) of females measured in March, in utero fetal count documented in March, and female age estimated in December. Fawn-specific covariates included age (days old), estimated mass at birth (kg), Julian date of birth, and sex (Bishop et al. 2009, Hurley et al. 2011. We incorporated fawn age into models by fitting a model that allowed transition probabilities to vary by an age trend from 0-14 days old and constant thereafter. ...
Article
Recent natural gas development has caused concern among wildlife managers, researchers, and stakeholders over the potential effects on wildlife and their habitats. Specifically, understanding how this development and other factors influence mule deer (Odocoileus hemionus) fawn (i.e., 0–6 months old) mortality rates, recruitment, and subsequently population dynamics have been identified as knowledge gaps. Thus, we tested predictions concerning the relationship between natural gas development, adult female, fawn birth, and temporal (weather) characteristics on fawn mortality in the Piceance Basin of northwestern Colorado, USA, from 2012–2014. We captured and radio‐collared 184 fawns and estimated apparent cause‐specific mortality in areas with relatively high or low levels of natural gas development using a multi‐state model. Mean daily predation probability was similar in the high versus low development areas. Predation was the leading cause of fawn mortality in both areas and decreased from 0–14 days old. Black bear (Ursus americanus; 22% of all mortalities, n = 17) and cougar (Felis concolor; 36% of all mortalities, n = 6) predation was the leading cause of mortality in the high and low development areas, respectively. Predation of fawns was negatively correlated with the distance from a female's core area to a producing well pad on winter or summer range. Contrary to expectations, predation of fawns was positively correlated with rump fat thickness of adult females. Well pad densities and development activity were relatively low during our study, indicating that the observed intensity of development did not appear to influence daily predation probability. Our results suggest maintaining development activity thresholds at levels we observed to potentially minimize the effects of development on fawn mortality. However, we caution that higher development intensity and drilling activity in flatter, less rugged areas with less concealment cover could influence fawn mortality. Managers should maintain low development densities in areas where topography and vegetation offer less concealment. Overall, region‐specific data (e.g., development intensity, topography, predator assemblages, and associated predation risk) are needed to better understand the effects of natural gas development on fawn mortality. © 2018 The Wildlife Society. We found that at the intensity and activity we observed, and under the environmental conditions acting during our study, natural gas development did not appear to influence fawn mortality overall, but there might have been effects to deer when closer to producing well pads. However, we caution that higher development intensity and drilling activity in flatter, less rugged areas could influence fawn mortality.
• ... Declines in mule deer (Odocoileus hemionus hemionus) population size and recruitment across much of the western United States have generated interest in understanding relationships between mule deer and their habitat requirements (Bishop et al. 2009, Tollefson et al. 2010, Bergman et al. 2015. Mule deer are an important social and economic species and it is necessary to identify the principal limiting factors affecting mule deer populations to guide management (Department of Interior 2018). ...
... Ungulates face numerous environmental constraints on their ability to survive and reproduce and declining nutrition because of loss or deterioration of habitat has been associated with observed declines (Peek et al. 2001, Cook et al. 2007, Shallow et al. 2015. Habitat quality (i.e., the ability of the environment to provide conditions appropriate for individual and population persistence [Hall et al. 1997]) has been reduced across historical mule deer range because of changing land management practices, overgrazing, exotic plant invasions, energy development, urbanization, and alteration of historical disturbance regimes (Hayden et al. 2008, Bishop et al. 2009, Cox et al. 2009). ...
... For decades, biologists have argued that the quality and quantity of forage on summer range were the best predictors of herd productivity in mule deer because summer nutrition influences population dynamics of large herbivores (Julander et al. 1961, Cook et al. 2004, Monteith et al. 2014. Specifically, summer forage conditions affect adult female body condition (Parker et al. 2009), which in turn predicts overwinter adult survival rates (Bender et al. 2007), pregnancy rates (Monteith et al. 2013), litter size (Tollefson et al. 2010), birth weight (Shallow et al. 2015), growth rate (Monteith et al. 2009, Freeman et al. 2013, and survival of offspring (Bishop et al. 2009, Tollefson et al. 2011, Hurley et al. 2017. Therefore, resources gained during summer influence most aspects of ungulate biology (Rowland et al. 2018). ...
Article
Mule deer (Odocoileus hemionus hemionus) populations have been declining throughout their range and loss or deterioration of habitat has been associated with observed trends. An understanding of the relative importance of landscape characteristics in affecting mule deer distribution will allow wildlife managers that alter habitat to make predictions regarding future use by mule deer, which is likely to influence mule deer population size and recruitment. We radio‐marked 376 adult female mule deer with global positioning system‐collars from 2006–2012 in south‐central Oregon, USA, to evaluate summer habitat use. We used multiple linear regression to develop a resource utilization function (RUF) model for mule deer to relate landscape characteristics to the height of a utilization distribution estimated with a Brownian bridge movement model. We validated the predictive capacity of the RUF model with locations from an independent dataset of 95 deer that summered within our study area. Our best model describing mule deer habitat use included 5 covariates: overstory canopy cover, slope, distance to forest edge, distance to intermittent or perennial streams, and distance to dirt roads. Predicted intensity of use peaked at roughly 40% canopy cover and decreased with increasing slope and distance from forest edge. Predicted use was greater closer to streams and decreased, albeit slightly, with increasing distance from dirt roads. Model validation revealed our model predicted summer habitat use by mule deer very well. Our results provide a basis for predicting effects of future land management actions on mule deer habitat use on summer range. Forest management prescriptions that maintain canopy cover around 40% and create forest edge may benefit mule deer in south‐central Oregon and other forested ecosystems, particularly if these prescriptions are implemented on areas with gentle slopes and access to streams. © 2019 The Wildlife Society. Our analysis of habitat use by mule deer on summer range indicated mule deer used areas with intermediate canopy cover, on low slopes, and closer to forest edges, streams, and dirt roads. Forest management prescriptions that maintain canopy cover around 40% and create forest edge may benefit mule deer in south‐central Oregon and other forested ecosystems, particularly if these prescriptions are implemented on areas with gentle slopes and access to streams.
• ... Biological factors, such as sex, birth mass, and date of birth, can influence neonate survival (Saalfield and Ditchkoff 2007, Bishop et al. 2009). Male neonates may be more susceptible to predation (Bishop et al. 2009) based on differences in activity patterns. ...
... Biological factors, such as sex, birth mass, and date of birth, can influence neonate survival (Saalfield and Ditchkoff 2007, Bishop et al. 2009). Male neonates may be more susceptible to predation (Bishop et al. 2009) based on differences in activity patterns. Jackson et al. (1972) reported that male neonates were more active than females, and male neonates have a propensity to be more independent of the dam (Taber and Dasmann 1954). ...
... The influence of date of birth on survival of neonates is variable. Many studies conducted where predation was a significant source of mortality on neonates reported no effect of birth date on survival (Vreeland et al. 2004, Saalfeld and Ditchkoff 2007, Chitwood et al. 2015b, whereas other research has documented that the probability of neonate survival was greatest for those born early in the season and declined with later birth dates (Lomas and Bender 2007, Bishop et al. 2009, Kilgo et al. 2012. This decline was attributed to stress, malnutrition, and disease on smaller, later-born young during winter, or to increases in nutritional demand or hunting skills of predators throughout the birthing season. ...
Article
Changing predator communities have potential to complicate management focused on ensuring sustainable white-tailed deer (Odocoileus virginianus) populations. Recent research reported that predation on neonates by coyotes (Canis latrans) and bobcats (Lynx rufus) can limit recruitment. However, no research has been conducted in areas of the southeastern United States with 3 sympatric neonate predators such as coyote, American black bear (Ursus americanus), and bobcat. Our objectives were to estimate neonate survival rates, identify causes of neonate mortality, and determine which biological and landscape characteristics were related to neonate survival. During 2013–2015, we captured 70 neonates with the aid of vaginal implant transmitters on Tensas River National Wildlife Refuge in northeastern Louisiana, USA. We monitored neonates every 8 hours until 6 weeks of age and daily until 12 weeks of age, and assigned cause of death from field and DNA evidence. Survival of neonates to 12 weeks was 0.271 (95% CI = 0.185–0.398). Of 51 mortalities, 45 (88%) were attributed to predation, 4 (8%) to starvation, 1 (2%) to other causes, and 1 (2%) to unknown causes. We used an information-theoretic approach to compare Cox proportional hazards models containing various combinations of biological and habitat covariates. Our best-supported model contained sex, mass at birth, distance to cropland, young reforestation (planted 2000–2009), and old reforestation (planted 1980–1989). Based on hazard ratios, survival was 81% higher for males than females, and survival increased 81% with every 1-kg increase in birth mass. Survival increased 8% for every 100-m increase in distance from cropland or young reforestation, and decreased 11% with every 100-m increase in distance from old reforestation, which may be a result of spatial variation in predator distribution. Our results emphasize the importance of site-specific monitoring of neonate recruitment rates in areas with burgeoning predator communities. We conclude, however, that although predation pressure was high, survival rates were similar to those observed in 2-predator systems in the region, suggesting the possibility that an upper limit to predation rates may exist for white-tailed deer neonates.
• ... Conception in Odocoileus has been related to maternal age (Anderson 1981, Verme and Ullrey 1984, Heffelfinger et al. 2003, Carstensen et al. 2009) and size or nutritional condition (Connolly 1981, Johnstone-Yellin et al. 2009, Tollefson et al. 2010. Litter size has also been related to age (Brown 1961, Parsons 1975 and maternal condition or size (Verme 1969, Ozoga and Verme 1982, Verme and Ullrey 1984, Bishop et al. 2009, Johnstone-Yellin et al. 2009, Tollefson et al. 2010. Maternal size or condition has similarly been related to fawn survival (Verme and Ullrey 1984, Johnstone-Yellin et al. 2009, Monteith et al. 2014). ...
... Declines in mule deer numbers are frequently attributed to low recruitment of fawns (Connolly 1981, Unsworth et al. 1999, Bishop et al. 2009, Bender et al. 2011. Thus, understanding which maternal and environmental factors most influence processes associated with productivity of mule deer in arid environments can help elucidate management actions to increase productivity of populations. ...
... Unlike most previous work (e.g. Robinette et al. 1973, Connolly 1981, Andelt et al. 2004, Heffelfinger 2006, Bishop et al. 2009), however, the age effect was not limited to yearling females, but also included older (i.e. age ≥8) females. ...
Article
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Mule deer Odocoileus hemionus (Rafinesque 1817) populations in southern New Mexico have declined significantly since the 1980s, similar to trends across the arid Southwestern USA. Because production of fawns is critical to population growth, we evaluated factors influencing fecundity in two mule deer populations in southern New Mexico. Conception, litter size and survival of ≥1 fawn to weaning were all affected by maternal age, with older (age 8 and older) females exhibiting reproductive senescence as compared to prime-aged (age 2–7) females for the latter two traits despite achieving similar condition as did prime-aged females. Litter size and survival to weaning were also positively affected by increasing spring precipitation and survival to weaning was also positively affected by increased maternal condition, and size during late gestation. Unlike most previous work, reproductive senescence was evident in mule deer in our study populations, possibly because deer in both populations were in poor condition and older females produced on average 0.24 (95% CI=0.10–0.42) fawns through weaning compared to 0.76 (95% CI=0.60–0.94) for prime-aged females. The positive effect of precipitation during gestation on litter size and fawn survival also indicated that both income (i.e. nutritional intake) and capital (i.e. body reserves) were important determinants of fecundity in our arid Southwestern populations. The relatively early onset of senescence compared to the lifespan of female mule deer indicates that more intensive management of female age structure may be necessary to enhance population-level productivity.
• ... Juvenile recruitment tends to be the most variable demographic vital rate among ungulates, ultimately having the greatest effect on population trajectory, although population growth rates are most sensitive to relatively constant adult female survival rates (Gaillard et al. 1998b(Gaillard et al. , 2000Haskell and Ballard 2007a;Bishop et al. 2009;Forrester and Wittmer 2013). Predation may be the major cause of fawn mortality in many white-tailed (Odocoileus virginianus) and mule deer (O. ...
... To understand the interrelatedness of mortality and habitat factors of sympatric white-tailed and mule deer in west-central Texas, we conducted a study to examine habitat-use relationships and population vital rates (Avey et al. 2003, Brunjes et al. 2006), during which annual variability in winter fawn recruitment was noted by road and aerial surveys. Few studies of survival of North American deer fawns have included fawns from marked females with multiple years of data (Kunkel and Mech 1994, Carstensen Powell et al. 2005, Bishop et al. 2009). These studies usually documented little fawn mortality due to causes other than predation, suggesting that those deer populations were well below K-carrying capacity. ...
... Expectation for observed mass gain is linear least squares with zero intercepts; expectation for captive fawns is from the literature (Verme 1963(Verme , 1989Murphy and Coates 1966;Robinette et al. 1973;Thompson et al. 1973;Robbins and Moen 1975). density-dependent effects on deer population vital rates in response to a fluctuating environment (Bishop et al. 2009, Forrester and Wittmer 2013, Monteith et al. 2014. ...
Article
Population growth rates of cervids are sensitive to changes in adult female survival, but fawn recruitment tends to be the population vital rate most susceptible to density-dependent population-level influences. We conducted a study of fawn survival rates and related biology in northwest Crockett County, Texas, USA, during 2004-2007 in an area where white-tailed deer (Odocoileus virginianus) and mule deer (O. hemionus eremicus) existed sympatrically. Our fawn study was justified by the need to explain annual variation in female-to-fawn ratios apparent during field surveys. Using vaginal implant transmitters in radio-marked adult females to locate birth sites, we captured, weighed, and radio-collared fawns on 4 privately owned ranches. We monitored collared fawns daily and investigated mortalities within 24hours of receiving a mortality signal to determine cause of death. When possible, we collected thymus glands to assess body condition. We captured 170 fawns (64 white-tailed deer; 106 mule deer), of which 145 were of known-age from collared females, and found that relatively heavy adult females birthed relatively heavy fawns. We also noted that mass gain of fawns and mass of fawns' thymus glands were very low compared to other studies of fawns. We documented mortalities: 47 by predation, 47 by sickness-starvation, 1 by conspecific trauma, and 3 undeterminable. Bobcats (Lynx rufus) were responsible for nearly all fawn predation; thymus gland and fawn mass data indicated that bobcats did not select weaker fawns. We used proportional hazards regression to assess factors influencing fawn survival and competing risks of mortality and made comparisons between the species when possible. We censored 6 fawns from our analyses and found that half of mortalities occurred within 15 days postpartum, and 12 of the 139 known-age fawns (9%) died within 25m of the birth site. Fawn survival was 78% at 6 days old, which was the median estimated age-at-capture of fawns from unknown adults. Annual fawn survival rate ranged from 50% for fawns born in 2004 to 17% for fawns born in 2006, with no overall effect of species. Fawn survival was greatest in 2004 when rain during the May-August late-gestation and lactation period was greatest. Mule deer fawns succumbed more to sickness-starvation than did white-tailed deer fawns. Rates of sickness-starvation and predation increased with deviance from mean annual birth dates and with reduced rain during the late-gestation and lactation period. Early fawn survival increased with relative fawn mass, and sex became important at about 30 days postpartum, after which males were at greater risk of sickness-starvation. Lunn-McNeil competing-risks models suggested some interaction between sickness-starvation and predation. Fawn mortality, mass gain, thymus mass, and weaning data indicated that the populations of both deer species were chronically stressed near a carrying capacity that fluctuated annually with rain and that adult females invested little energy in rearing fawns relative to captive females.
• ... Similarly, we had no way of knowing which animals may have nursed twins and for how long, 2 factors that are influential to individual condition (i.e., as evidenced by observation of adult female deer with fawns during fall being highly influential for individual condition; Monteith et al. 2013). Previous authors have noted that pregnancy status at the time of capture can be correlated with body condition, although those correlations have tended to be weak (Bishop et al. 2009b, Bergman et al. 2014). The correlation is weak likely because pregnancy rates in mule deer, especially in western Colorado, tend to be high and largely invariant (Bishop et al. 2009a, b;Bergman et al. 2014). ...
... In particular, hunter-harvested samples would not reflect the effects of winter because harvest typically occurs during autumn. The effect of fawn mass on overwinter survival of fawns has been reported in Colorado and elsewhere (Unsworth et al. 1999, Bishop et al. 2009b, Hurley et al. 2011. Estimates of short-yearling mass (i.e., 10 months old) of moose (Alces alces) has been used for evaluation of herd nutritional status (Boertje et al. 2007). ...
... Likewise, we caution against the inference of our results from mule deer to other large ungulates. For instance, the majority of mule deer in Colorado have 2 fetuses per year (Bishop et al. 2009b). Thus, the annual reproductive output of individual animals has the potential to be highly variable (i.e., mature deer may nurse 0, 1, or 2 fawns for different periods of time, depending on timing of fawn mortality). ...
Article
The use of ultrasonograhic measurements of muscle and body fat represent a relatively new data stream that can be used to address questions regarding ungulate condition. We have learned that measurements of body fat and presumably overall body condition among individual animals, even those taken from the same herd at that same time, are highly variable. Relatively little consideration has been given to the sources of variation in body fat and other physiological parameters in wildlife populations. We evaluated the components of variation in late-winter mule deer (Odocoileus hemionus) body fat estimates: sampling variation (i.e., variation induced by the particular set of individuals that were sampled) and process variation (i.e., variation stemming from biological processes) with a long-term data set (2002–2015) from Colorado, USA. We collected our data from across Colorado as part of historical research, ongoing research, and periodic population monitoring programs. Mean percent ingesta-free body fat (%IFBF) for sampled mule deer was 7.20 ± 1.20% (SD). Covariates related to individual deer explained approximately 4% of the total variation in %IFBF and annual effects explained an additional 13% of the variation. Substantial residual variation in %IFBF (83%) remained unexplained. The source of the 83% of unexplained variation is partially linked to fine-scale spatial dynamics but also additional individual metrics we were unable to capture, primarily the presence or absence of dependent young. We speculate that the primary factors influencing late-winter mule deer body fat and overall condition are individual in nature. These results present a cautionary check on herd-level inference that can be made from individual late-winter body fat estimates and we postulate that for mule deer, alternative and additional body condition metrics may offer added utility in management scenarios. However, an important next step to better understand wildlife population health is to evaluate the sources and magnitude of variation within other body condition metrics, with the goal of further refining data that can better allow biologists to incorporate herd health into population management recommendations.
• ... If an adult female was pregnant, we inserted a vaginal implant transmitter (VIT; Model M3930, Advanced Telemetry Systems) following VIT insertion procedures described in detail by Bishop et al. (2011) and Peterson (2016). Helicopter net gunning and vaginal implant transmitters have been used without influencing reproductive success and are effective methods to capture females and neonates (Carstensen et al. 2003, Bishop et al. 2009, Monteith et al. 2014). ...
... We assumed fetal survival data were not overdispersed based on the recommendation of Bishop et al. (2008). Lastly, we fit the same model set for reproductive success metrics as Bishop et al. (2009), except age class, and that we hypothesized would influence reproductive success. ...
... We found pregnancy and in utero fetal rates were high, showed little variation across years, and were similar in the high versus low development areas. Bishop et al. (2009) found no difference in pregnancy and in utero fetal rates when examining the effects of supplemental nutrition treatments versus a control group in a different area of Colorado and Anderson (2016) found no difference in body condition of adult females between the high and low development areas in our study area. Pregnancy and fetal rates were high in each area and in the upper range of previous estimates (0.860-1.000 and 1.650-2.010, ...
Article
Full-text available
Natural gas development is increasing across North America and causing concern over the potential impacts on wildlife populations and their habitat, particularly for ungulate species. Understanding how this development impacts reproductive success metrics that are influential for ungulate population dynamics is important to guide management of ungulates. However, the influences of natural gas development on reproductive success metrics of mule deer (Odocoileus hemionus) have not been studied. We used statistical models to examine the influence of natural gas development and temporal factors on reproductive success metrics of mule deer in the Piceance Basin, northwest Colorado during 2012–2014. We focused on study areas with relatively high or low levels of natural gas development. Pregnancy and in utero fetal rates were high and statistically indistinguishable between study areas. Fetal survival rates increased over time and survival was lower in the high versus low development study areas in 2012 possibly influenced by drought coupled with habitat loss and fragmentation associated with development. Our novel results suggest managers should be concerned with the influences of development on fetal survival, particularly during extreme environmental conditions (e.g., drought) and our results can be used to guide development planning and/or mitigation. Developers and wildlife managers should continue to collaborate on development planning, such as implementing habitat treatments to improve forage availability and quality, minimizing disturbance to hiding and foraging habitat particularly during parturition, and implementing directional drilling to minimize pad disturbance density to increase fetal survival in developed areas.
• ... To better understand how maternal movement rates reflect parturition dates, knowing movement and parturition dates with minimal error is needed. The use of vaginal implant transmitters (VITs) allow for limited error in determining parturition dates and locations, but is costly (Bishop et al. 2009(Bishop et al. , 2011Carstensen et al. 2009). Relying upon maternal deer movement rates to identify parturition dates is cheaper and easier, but has not been validated with VITs. ...
... We also suggest that a maternal deer whose daily movement rate decreases by !46% has given birth (i.e., rule 1). Restricted movement of females after parturition may be attributable to fawns that are entirely dependent on a hiding strategy for survival because of vulnerability to predation (Lent 1974, Geist 1981, Bishop et al. 2009, Monteith et al. 2014, Shallow et al. 2015. ...
• ... Mule deer populations are known to fluctuate, but significant decreases in population estimates across multiple western states have generated concern, as mule deer are an iconic species with tremendous ecological, recreational, and economic value. Drivers of mule deer declines are largely unknown, and likely multifaceted, but evidence suggests that habitat conditions play a pivotal role (Gill, 2001;Bishop et al., 2009;Hurley et al., 2014;Monteith et al., 2014;Shallow et al., 2015). To date, research on habitat has primarily focused on the influence of forage quality, cover type, and local climate conditions on mule deer dynamics, but land-use change may also be important (Polfus & Krausman, 2012). ...
... Variation in forage quality, harvest, predation, disease and interspecific competition (with domestic livestock and wild ungulates) can all influence ungulate demographic rates (Gross & Miller, 2001;Cook et al., 2004;Bergman et al., 2011;Brodie et al., 2013;Hurley et al., 2014). While we did not have data with comparable spatial or temporal extents to investigate these other factors, we suspect that some are highly important in the dynamics of deer across our study area (e.g., forage quality; Bishop et al., 2009;Bergman et al., 2014). For those land-use and weather factors that we did investigate, their long-term temporal trends are highly disconcerting for mule deer. ...
Article
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Land-use change due to anthropogenic development is pervasive across the globe and commonly associated with negative consequences for biodiversity. While land-use change has been linked to shifts in the behavior and habitat-use patterns of wildlife species, little is known about its influence on animal population dynamics, despite the relevance of such information for conservation. We conducted the first broad-scale investigation correlating temporal patterns of land-use change with the demographic rates of mule deer, an iconic species in the western United States experiencing wide-scale population declines. We employed a unique combination of long-term (1980–2010) data on residential and energy development across western Colorado, in conjunction with congruent data on deer recruitment, to quantify annual changes in land-use and correlate those changes with annual indices of demographic performance. We also examined annual variation in weather conditions, which are well recognized to influence ungulate productivity, and provided a basis for comparing the relative strength of different covariates in their association with deer recruitment. Using linear mixed models, we found that increasing residential and energy development within deer habitat were correlated with declining recruitment rates, particularly within seasonal winter ranges. Residential housing had two times the magnitude of effect of any other factor we investigated, and energy development had an effect size similar to key weather variables known to be important to ungulate dynamics. This analysis is the first to correlate a demographic response in mule deer with residential and energy development at large spatial extents relevant to population performance, suggesting that further increases in these development types on deer ranges are not compatible with the goal of maintaining highly productive deer populations. Our results underscore the significance of expanding residential development on mule deer populations, a factor that has received little research attention in recent years, despite its rapidly increasing footprint across the landscape.
• ... This interpretation was also supported by the direct negative effects of winter severity on overwinter elk calf survival. Although the effect was not statistically strong in our study, previous juvenile winter survival studies report that increasing winter snow precipitation decreases winter survival of ungulates (Bishop et al. 2009, Hurley et al. 2014. ...
... Therefore, in declining elk populations with recovering carnivores, reducing adult female harvest may be initially necessary as carnivores recover to allow time to identify the most effective strategy to balance ungulate and carnivore management objectives. As carnivore recovery continues, managers may need to consider a more aggressive policy toward habitat restoration (e.g., logging, prescribed burns) or carnivore management for ungulates in less productive habitats, while developing adaptive management experiments to ensure that management can disentangle the bottom-up and top-down effects on ungulates (Hayes et al. 2003, Bishop et al. 2009. ...
Article
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The realized effect of multiple carnivores on juvenile ungulate recruitment may depend on the carnivore assemblage as well as compensation from forage and winter weather severity, which may mediate juvenile vulnerability to predation in ungulates. We used a time-to-event approach to test for the effects of risk factors on annual elk (Cervus canadensis) calf survival and to estimate cause-specific mortality rates for 2 elk populations in adjacent study areas in the southern Bitterroot Valley, Montana, USA, during 2011–2014. We captured and radio-tagged 286 elk calves: 226 neonates, and 60 6-month-old calves. Summer survival probability was less variable than winter (P = 0.12) and averaged 0.55 (95% CI = 0.47–0.63), whereas winter survival varied more than summer and significantly across study years (P = 0.003) and averaged 0.73 (95% CI = 0.64–0.81). During summer, elk calf survival increased with biomass of preferred forage biomass, and was slightly lower following winters with high precipitation; exposure to mountain lion (Puma concolor) predation risk was unimportant. In contrast, during winter, we found that exposure to mountain lion predation risk influenced survival, with a weak negative effect of winter precipitation. We found no evidence that forage availability or winter weather severity mediated vulnerability to mountain lion predation risk in summer or winter (e.g., an interaction), indicating that the effect of mountain lion predation was constant regardless of spatial variation in forage or weather. Mountain lions dominated known causes of elk calf mortality in summer and winter, with estimated cause-specific mortality rates of 0.14 (95% CI = 0.09–0.20) and 0.12 (95% CI = 0.07–0.18), respectively. The effect of carnivores on juvenile ungulate recruitment varies across ecological systems depending on relative carnivore densities. Mountain lions may be the most important carnivore for ungulates, especially where grizzly bears (Ursus arctos) and wolves (Canis lupus) are rare or recovering. Finally, managers may need to reduce adult female harvest of elk as carnivores recolonize to balance carnivore and ungulate management objectives, especially in less productive habitats for elk.
• ... An important implication is that differences in migration timing and residency on winter range effectively decrease time on winter range during a time of year critical to survival and reproduction (Parker et al. 2009). In temperate regions, most ungulates experience a nutritional bottleneck during winter when forage is lower in digestibility and protein content, and animals are often concentrated at their highest year-round densities (Bishop et al. 2009, Monteith et al. 2011, resulting in important feedbacks into density-dependent mortality and population dynamics (Bartmann et al. 1992. ...
... We hypothesize that long-distance migrants enhanced their own net nutritional gain by occupying a third seasonal range (i.e., the migration route) and, consequently, increased the potential carrying capacity for the overall herd. In our case, 30% of the deer herd (i.e., long-distance migrants) reduced winter residency by more than three months; such a reduction in occupancy of winter range has a clear potential to increase carrying capacity for herds limited by winter range, which has often been reported (Bishop et al. 2009). Notably, reduced residency on winter range only occurred with long-distance migrants. ...
Article
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Partial migration occurs across a variety of taxa and has important ecological and evolutionary consequences. Among ungulates, studies of partially migratory populations have allowed researchers to compare and contrast performance metrics of migrants versus residents and examine how environmental factors influence the relative abundance of each. Such studies tend to characterize animals discretely as either migratory or resident, but we suggest that variable migration distances within migratory herds are an important and overlooked form of population structure, with potential consequences for animal fitness. We examined whether the variation in individual migration distances (20–264 km) within a single wintering population of mule deer (Odocoileus hemionus) was associated with several critical behavioral attributes of migration, including timing of migration, time allocation to seasonal ranges, and exposure to anthropogenic mortality risks. Both the timing of migration and the amount of time animals allocated to seasonal ranges varied with migration distance. Animals migrating long distances (150–250 km) initiated spring migration more than three weeks before than those migrating moderate (50–150 km) or short distances (<50 km). Across an entire year, long-distance migrants spent approximately 100 more days migrating compared to moderate- and short-distance migrants. Relatedly, winter residency of long-distance migrants was 71 d fewer than for animals migrating shorter distances. Exposure to anthropogenic mortality factors, including highways and fences, was high for long-distance migrants, whereas vulnerability to harvest was high for short- and moderate-distance migrants. By reducing the amount of time that animals spend on winter range, long-distance migration may alleviate intraspecific competition for limited forage and effectively increase carrying capacity. Clear differences in winter residency, migration duration, and risk of anthropogenic mortality among short-, moderate-, and long-distance migrants suggest fitness trade-offs may exist among migratory segments of the population. Future studies of partial migration may benefit from expanding comparisons of residents and migrants, to consider how variable migration distances of migrants may influence the costs and benefits of migration.
• ... In cervids, lactation generally lowers body condition in all cases less than optimal nutrition (Clutton-Brock et al. 1982, Piasecke and Bender 2009, Minami et al. 2012, Simard et al. 2014). Thus, current reproduction can potentially negatively affect future reproduction because most reproductive processes are associated with condition, including probability of pregnancy (Ozoga and Verme 1982, Tollefson et al. 2010, Minami et al. 2012, birth attributes of juveniles (Verme and Ullrey 1984, Hoenes 2008, and survival of juveniles , Hoenes 2008, Bishop et al. 2009). However, while lactating females are usually in poorer condition going into winter than dry females , Minami et al. 2012), these differences may not persist into spring (Clutton-Brock et al. 1982, Piasecke and. ...
... Nor was survival of females related to current or previous lactation status in our populations . Mule deer have a single birth period annually, and early survival of mule deer neonates is strongly dependent upon maternal condition , Hoenes 2008, Bishop et al. 2009) and birth attributes including birth mass and birth date Bender 2007, Hoenes 2008), which in turn are related to maternal condition. Because of convergence in condition over winter, both previous lactating and dry females enter late gestation in comparable condition. ...
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We compared indices of nutritional condition and size between lactating and dry ≥2.5-year-old mule deer Odocoileus hemionus from three free-ranging populations in the Southwestern USA to quantify the energetic costs of lactation on endogenous energy reserves, determine whether differences persisted over winter, and assess carryover effects on future reproduction. In autumn, dry and lactating females differed in 77% of comparisons of condition and 20% of comparisons of size among population-years. In all significant comparisons, dry females were in better condition than lactating, and were smaller. Accrual of fat reserves was affected by lactation more than were protein reserves or size, but of those variables in which dry females differed from lactating in autumn, differences were lost by spring in 100% of cases. Accrual of some indices of condition was negatively affected by consecutive years of full lactations, but this effect was small compared to the overall magnitude of the lactation effect. Neither pregnancy, litter size, birth mass, nor survival of fawns to 30 days or to weaning were affected by previous successful reproduction, while birth date showed a weak positive effect. Likely because of convergence in condition overwinter, the negative influence of lactation on condition did not have a significant carryover effect on future reproduction. Because our study populations experienced moderate to severe nutritional stress, lack of a carryover effect is likely valid for most mule deer populations.
• ... Additionally, previous investigators have shown pregnancy rates and fetal rates to be high and consistent (Andelt, Pojar, & Johnson, 2004;Bishop, White, Freddy, Watkins, & Stephenson, 2009). Therefore, juvenile survival and recruitment may be the best indicators of population performance (Gaillard, Festa-Bianchet, & Yoccoz, 1998). ...
... This variation in habitat use allows investigators to evaluate population responses to many different environmental factors. Similar to other large herbivores, adult mule deer exhibit high and stable survival rates throughout most of their geographical range (Bender, Hoenes, & Rodden, 2012;Bishop et al., 2009;Hurley et al., 2011;Monteith et al., 2014). Given the importance of the influence of juvenile survival on population performance (Gaillard et al., 1998), our objectives were to evaluate and quantify factors influencing juvenile survival in an arid environment. ...
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Climate models predict that shifts in temperature and precipitation patterns are likely to occur across the globe. Changing climate will likely have strong effects on arid environments as a result of increased temperatures, increasing frequency and intensity of droughts, and less consistent pulses of rainfall. Therefore, understanding the link between patterns of precipitation, temperature, and population performance of species occupying these environments will continue to increase in importance as climatic shifts occur within these natural ecosystems. We sought to evaluate how individual, maternal, population, and environmental, particularly temperature and precipitation, level factors influence population performance of a large herbivore in an arid environment. We used mule deer (Odocoileus hemionus) as a representative species and quantified juvenile survival to test hypotheses about effects of environmental factors on population performance. Precipitation events occurring in mid- to late-pregnancy (January–April) leading to spring green-up, as indexed by normalized difference in vegetation index, had the strongest positive effect on juvenile survival and recruitment. In addition, larger neonates had an increased probability of survival. Our findings indicate that timing and amount of precipitation prior to parturition have strong influences on maternal nutritional condition, which was passed on to young. These results have important implications for understanding how animal populations may benefit from timing of precipitation during spring and prior to parturition, especially in arid environments.
• ... Increases in juniper cover across mule deer winter range, however, may have negatively affected forage availability for mule deer because abundance of shrubs, forbs, and grasses decline in juniper stands (Miller et al. 2000, Peek et al. 2001. Past research has indicated that nutritional resources during winter can influence survival and population dynamics of mule deer (Baker and Hobbs 1985, Bishop et al. 2009, Bergman et al. 2014 and if increases in juniper cover have reduced forage quantity and quality for mule deer, this could have populationlevel consequences. Given the lack of knowledge on effects of juniper treatments on mule deer habitat use and demography, future research to elucidate effects of juniper removal on mule deer is warranted. ...
... In a metaanalysis of the effects of flight responses of ungulates to human disturbance, it was found that ungulates, including mule deer, had a strong avoidance and increased movement rates in response to human activity, especially for hunted populations (Stankowich 2008) like our study populations in south-central Oregon. Consequently, human disturbance associated with motorized vehicle use on roads may cause mule deer to increase movement rates, leading to a net reduction in their energy budget, which could ultimately have demographic consequences (Robinette et al. 1973, Bishop et al. 2009, Tollefson et al. 2010. Fortunately, given that ungulates likely respond to the disturbance associated with motorized vehicle use of roads and not the road itself, this situation can be rectified through seasonal or permanent road closures. ...
• ... The result of timing parturition to a monsoonal-driven growing season can be nutritional stress during the most demanding parts of the reproductive schedule. The relationship between environmental productivity, maternal nutrition, and juvenile survival has been demonstrated in other Great Basin and Rocky Mountain mule deer populations [8,67], in which body condition predicted vulnerability to predation and annual survival rates for both juveniles and adults. ...
... In that sense, migration provides a means of reducing variability in diet quality through time. This general relationship has been validated through subsequent studies conducted on ungulate behavior in arctic, tropical, and temperate ecosystems [5,18,23,52,67,69,70]. Our study focused on migratory mule deer in a region characterized by high spatial and seasonal variability in precipitation. ...
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The effect of climatically-driven plant phenology on mammalian reproduction is one key to predicting species-specific demographic responses to climate change. Large ungulates face their greatest energetic demands from the later stages of pregnancy through weaning, and so in seasonal environments parturition dates should match periods of high primary productivity. Interannual variation in weather influences the quality and timing of forage availability, which can influence neonatal survival. Here, we evaluated macro-scale patterns in reproductive performance of a widely distributed ungulate (mule deer, Odocoileus hemionus) across contrasting climatological regimes using satellite-derived indices of primary productivity and plant phenology over eight degrees of latitude (890 km) in the American Southwest. The dataset comprised > 180,000 animal observations taken from 54 populations over eight years (2004-2011). Regionally, both the start and peak of growing season ("Start" and "Peak", respectively) are negatively and significantly correlated with latitude, an unusual pattern stemming from a change in the dominance of spring snowmelt in the north to the influence of the North American Monsoon in the south. Corresponding to the timing and variation in both the Start and Peak, mule deer reproduction was latest, lowest, and most variable at lower latitudes where plant phenology is timed to the onset of monsoonal moisture. Parturition dates closely tracked the growing season across space, lagging behind the Start and preceding the Peak by 27 and 23 days, respectively. Mean juvenile production increased, and variation decreased, with increasing latitude. Temporally, juvenile production was best predicted by primary productivity during summer, which encompassed late pregnancy, parturition, and early lactation. Our findings offer a parsimonious explanation of two key reproductive parameters in ungulate demography, timing of parturition and mean annual production, across latitude and changing climatological regimes. Practically, this demonstrates the potential for broad-scale modeling of couplings between climate, plant phenology, and animal populations using space-borne observations.
• ... During the past 25 years, mule deer (Odocoileus hemionus hemionus) populations have declined throughout much of their range in the western United States (Ballard et al. 2001, Bishop et al. 2009, Bergman et al. 2015. Mechanisms of mule deer population declines are largely unknown and probably complex, although deteriorating habitat conditions are likely a contributing factor (Peek et al. 2001, Monteith et al. 2014). ...
... Mechanisms of mule deer population declines are largely unknown and probably complex, although deteriorating habitat conditions are likely a contributing factor (Peek et al. 2001, Monteith et al. 2014). Habitat quality is thought to have been reduced across much of the mule deer range because of changing land-management practices, unmanaged grazing, exotic plant invasions, energy development, urbanization, and alteration of historical disturbance regimes (Bishop et al. 2009). In addition to effects on population demography, such reductions in habitat quality may alter mule deer habitat use or displace deer from their traditional ranges (Lendrum et al. 2012). ...
Article
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Mule deer (Odocoileus hemionus hemionus) populations have been declining throughout their range and deteriorating habitat conditions are likely one cause of these declines. Reductions in food and cover availability along traditional routes may especially influence habitat use during migration by mule deer. Forest management practices such as underburning, the practice of using low‐severity fires to reduce fuel loads, are often assumed to be beneficial to deer through enhancement of forage quality and quantity. However, these practices may be detrimental to mule deer through decreases in food and cover availability. Currently, little is known about the effects of underburning on habitat use by mule deer during migration. We analyzed Global Positioning System tracking data from 187 adult female mule deer in central Oregon, USA, from 2005 to 2012 in relation to 243 areas that were underburned between 1977 and 2009 to assess effects of underburning on habitat use during seasonal migrations. During spring migration, mule deer decreased use of recently underburned (i.e., ≤7 years‐since‐burned) areas compared with pretreatment use. There was not a difference in use of recently underburned areas before and after treatment during autumn migration. In spring, the proportion of used underburned areas declined postburn without recovering to preburn levels up to 20 years after treatment. The proportion of underburned areas used in autumn was much more variable, with use of postburn areas fluctuating above the preburn mean but never reaching the preburn maximum. We contend that reductions in forage and cover availability from underburning may negatively affect migrating mule deer, especially during spring. Thus, efforts should be taken to minimize burning large, continuous areas along migration routes and avoid burning adjacent areas during the same year to maintain a diverse mosaic of understory age classes, which will allow deer to make habitat use choices during migration.
• ... migratory route) influence the survival of individuals. Past studies have linked the survival of large herbivores to weather patterns, vegetation, predation risk (Bender, Lomas, & Browning, 2007;DeCesare et al., 2014) and other factors known to directly affect or index nutritional condition (Bishop, White, Freddy, Watkins, & Stephenson, 2009;Monteith et al., 2013Monteith et al., , 2014. ...
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• ... Bolger et al. (2008) observed that for many mammalian species (e.g., wildebeest, Connochaetes taurinus, Ottichilo et al. 2001; zebra, Equis burchelli, Williamson and Williamson 1985; and mule deer, Odocoileus hemionus, Bertram and Rempel 1977), the disruption of migratory routes has caused rapid population collapses. Indeed, populations of mule deer have declined throughout much of the Intermountain West, USA (Unsworth et al. 1999, Johnson et al. 2000, Stewart et al. 2002, Bishop et al. 2009, Hurley et al. 2011, and unprecedented levels of energy development throughout the region represent a critical threat to traditional migration routes for mule deer (Copeland et al. 2009). In particular, effects of natural-gas development can include the direct loss of habitat around well pads, access roads, and pipeline constructions, as well as indirect losses caused by increased human disturbance (e.g., traffic, noise) associated with infrastructure. ...
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• ... Lower quality forage on winter range has the potential to affect reproductive performance and population demographics in several ways (Raedeke et al. 2002). Winter range nutrition may affect overwinter survival of juvenile or adult ungulates (Cook et al. 2004, Bishop et al. 2009). Additionally, the female may devote less energy to gestation if she is nutritionally stressed, potentially resulting in lower calf birth weight (Carstens et al. 1987). ...
Article
Understanding how habitat and nutritional condition affect ungulate populations is necessary for informing management, particularly in areas experiencing carnivore recovery and declining ungulate population trends. Variations in forage species availability, plant phenological stage, and the abundance of forage make it challenging to understand landscape-level effects of nutrition on ungulates. We developed an integrated spatial modeling approach to estimate landscape-level elk (Cervus elaphus) nutritional resources in two adjacent study areas that differed in coarse measures of habitat quality and related the consequences of differences in nutritional resources to elk body condition and pregnancy rates. We found no support for differences in dry matter digestibility between plant samples or in phenological stage based on ground sampling plots in the two study areas. Our index of nutritional resources, measured as digestible forage biomass, varied among land cover types and between study areas. We found that altered plant composition following fires was the biggest driver of differences in nutritional resources, suggesting that maintaining a mosaic of fire history and distribution will likely benefit ungulate populations. Study area, lactation status, and year affected fall body fat of adult female elk. Elk in the study area exposed to lower summer range nutritional resources had lower nutritional condition entering winter. These differences in nutritional condition resulted in differences in pregnancy rate, with average pregnancy rates of 89% for elk exposed to higher nutritional resources and 72% for elk exposed to lower nutritional resources. Summer range nutritional resources have the potential to limit elk pregnancy rate and calf production, and these nutritional limitations may predispose elk to be more sensitive to the effects of harvest or predation. Wildlife managers should identify ungulate populations that are nutritionally limited and recognize that these populations may be more impacted by recovering carnivores or harvest than populations inhabiting more productive summer habitats.
• ... Therefore, we hypothesize that fawns are more vulnerable to mortality during this time. Other studies have reported fawn birth mass to be positively associated with survival (Lomas and Bender, 2007;Bishop et al., 2009;Hurley et al., 2011). We expected to find a similar association in our study; however, none of the individual covariates that we assessed in our summer survival analysis, including birth mass, were related to summer fawn survival. ...
Article
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Desert mule deer (Odocoileus hemionus eremicus) densities in central Arizona are below historic levels, likely due to neonatal mortality influencing desert mule deer population dynamics. However, no direct assessments have been made into causes and timing of neonatal mortalities in central Arizona. The objectives of our study were to determine the causes and timing of mortalities of desert mule deer fawns, estimate the annual survival rate of adult females and fawns, and quantify predator effects on fawn survival. In 2007 and 2008 we captured 52 adult female desert mule deer and equipped pregnant females with vaginal implant transmitters to aid in capturing fawns. We performed survival analyses using Program MARK and compared competing models with Akaike's information criterion. We captured 44 desert mule deer fawns; summer survival was 0.432 (95% CI = 0.292–0.584) and annual fawn survival was 0.071 (95% CI = 0.013–0.303). Predation accounted for 64% of fawn mortality. Probability of fawn survival was lowest in the first 2 weeks postparturition. Most (50 of 51) adult females of breeding age were pregnant and adult female survival was 0.858 (95% CI = 0.766–0.961). High predation rates and timing of predation on mule deer fawns were important factors influencing deer densities in central Arizona.
• ... The relative importance of summer versus winter survival to variation in population dynamics may vary, but was approximately equal in a nearby elk population (Eacker et al. 2017). Nonetheless, the primary driver of overwinter juvenile survival was juvenile mass at 6 months of age (Hurley et al., 2014), which was driven by forage productivity from 0 to 6 months of age (see also Bishop, White, Freddy, Watkins, & Stephenson, 2009). Thus, competition for high-quality juvenile-rearing habitat during summer, and the ensuing spatial density dependence it causes (Bergman et al., 2015), may set the stage for the relative importance of summer versus winter juvenile survival to population dynamics in large herbivores where competition for high-quality juvenile-rearing habitat occurs (e.g., roe deer, whitetailed deer). ...
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Density‐dependent competition for food reduces vital rates, with juvenile survival often the first to decline. A clear prediction of food‐based, density‐dependent competition for large herbivores is decreasing juvenile survival with increasing density. However, competition for enemy‐free space could also be a significant mechanism for density dependence in territorial species. How juvenile survival is predicted to change across density depends critically on the nature of predator–prey dynamics and spatial overlap among predator and prey, especially in multiple‐predator systems. Here, we used a management experiment that reduced densities of a generalist predator, coyotes, and specialist predator, mountain lions, over a 5‐year period to test for spatial density dependence mediated by predation on juvenile mule deer in Idaho, USA. We tested the spatial density‐dependence hypothesis by tracking the fate of 251 juvenile mule deer, estimating cause‐specific mortality, and testing responses to changes in deer density and predator abundance. Overall juvenile mortality did not increase with deer density, but generalist coyote‐caused mortality did, but not when coyote density was reduced experimentally. Mountain lion‐caused mortality did not change with deer density in the reference area in contradiction of the food‐based competition hypothesis, but declined in the treatment area, opposite to the pattern of coyotes. These observations clearly reject the food‐based density‐dependence hypothesis for juvenile mule deer. Instead, our results provide support for the spatial density‐dependence hypothesis that competition for enemy‐free space increases predation by generalist predators on juvenile large herbivores.
• ... These estimates were similar, albeit slightly lower than our estimates. Our estimates incorporated survival information through August, a period when juvenile mule deer survival tends to be higher than in the first four weeks of life (Bishop et al. 2009;Heffelfinger et al. 2018). The period for our survival estimates was determined by our survey design, which can be tailored to any period of interest. ...
Article
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Methods for estimating juvenile survival of wildlife populations often rely on intensive data collection efforts to capture and uniquely mark individual juveniles and observe them through time. Capturing juveniles in a time frame sufficient to estimate survival can be challenging due to narrow and stochastic windows of opportunity. For many animals, juvenile survival depends on postnatal parental care (e.g., lactating mammals). When a marked adult gives birth to, and provides care for, juvenile animals, investigators can use the adult mark to locate and count unmarked juveniles. Our objective was to leverage the dependency between juveniles and adults and develop a framework for estimating reproductive rates, juvenile survival, and detection probability using repeated observations of marked adult animals with known fates, but imperfect detection probability, and unmarked juveniles with unknown fates. Our methods assume population closure for adults and that no juvenile births or adoptions take place after monitoring has begun. We conducted simulations to evaluate methods and then developed a field study to examine our methods using real data consisting of a population of mule deer in a remote area in central Nevada. Using simulations, we found that our methods were able to recover the true values used to generate the data well. Estimates of juvenile survival rates from our field study were 0.96, (95% CRI 0.83–0.99) for approximately 32-day periods between late June and late August. The methods we describe show promise for many applications and study systems with similar data types, and our methods can be easily extended to unmanned aerial platforms and cameras that are already commercially available for the types of images we used. Supplementary materials accompanying this paper appear online.
• ... covariates, including CWD-status, on the probability of pregnancy, which is an important vital rate to understand the population dynamics as it relates to CWD. We used PROC LOGISTIC to perform a logistic regression analysis [22] on probability of pregnancy (event = 1) given CWD-status (CWD), age, body condition score (BCS) at time of capture, and year of capture (year). No fawn ( 8 months) deer were pregnant, so that age class was excluded from analysis. ...
Article
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Chronic wasting disease (CWD) is an invariably fatal transmissible spongiform encephalopathy of white-tailed deer, mule deer, elk, and moose. Despite a 100% fatality rate, areas of high prevalence, and increasingly expanding geographic endemic areas, little is known about the population-level effects of CWD in deer. To investigate these effects, we tested the null hypothesis that high prevalence CWD did not negatively impact white-tailed deer population sustainability. The specific objectives of the study were to monitor CWD-positive and CWD-negative white-tailed deer in a high-prevalence CWD area longitudinally via radio-telemetry and global positioning system (GPS) collars. For the two populations, we determined the following: a) demographic and disease indices, b) annual survival, and c) finite rate of population growth (λ). The CWD prevalence was higher in females (42%) than males (28.8%) and hunter harvest and clinical CWD were the most frequent causes of mortality, with CWD-positive deer over-represented in harvest and total mortalities. Survival was significantly lower for CWD-positive deer and separately by sex; CWD-positive deer were 4.5 times more likely to die annually than CWD-negative deer while bucks were 1.7 times more likely to die than does. Population λ was 0.896 (0.859-0.980), which indicated a 10.4% annual decline. We show that a chronic disease that becomes endemic in wildlife populations has the potential to be population-limiting and the strong population-level effects of CWD suggest affected populations are not sustainable at high disease prevalence under current harvest levels.
• ... Multiple interacting factors influence mule deer population dynamics, but survival, as it relates to forage quality, has been identified as a significant driver (Unsworth et al. 1999;Bishop et al. 2009;Tollefson et al. 2011). Nutritious forbs and shrubs are especially important for overwinter survival of mule deer (Bartmann 1983), but availability within and between stands of pinyon-juniper can vary greatly. ...
Article
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Pinyon-juniper (Pinus spp.–Juniperus spp.) encroachment and declining mule deer (Odocoileus hemionus) populations in western Colorado have necessitated management for increased forage. Pinyon-juniper removal is one such technique; however, it is unclear which method of tree removal most effectively promotes forage species. We conducted an experiment to quantify understory responses to mechanical pinyon-juniper removal and seed additions in a blocked design using three different methods: anchor-chaining, rollerchopping, and mastication. Blocks contained each mechanical and seeding treatment along with an untreated control. Seven blocks across two sites, North Magnolia (NM, 4 blocks) and South Magnolia (SM, 3 blocks), were treated during the fall of 2011. Half of each plot was seeded before or during mechanical treatment with a mix of grasses, shrubs, and forbs. After two growing seasons, biomass of perennial grasses was 90–160 kg · ha− 1 in mechanically treated plots compared with 10 kg · ha− 1 in untreated controls. There were no differences, however, between mechanical treatments for any perennial plant species. Response of annual plant species depended on mechanical treatment type and site. Rollerchopping had higher exotic annual grass cover than mastication or control at NM and higher exotic annual forb cover than chaining or control at SM. Rollerchopping was the only treatment to have higher native annual forb cover than control in the absence of seeding. Seeding increased native annual forb biomass in mastication compared with control. Seeding also increased shrub density at SM, which had fewer shrubs pretreatment relative to NM. Results suggest any type of mechanical removal of pinyon-juniper can increase understory plant biomass and cover. Seeding in conjunction with mechanical treatments, particularly mastication, can initially increase annual forb biomass and shrub density. Finally, different understory responses between sites suggests that pretreatment conditions are important for determining outcomes of pinyon-juniper removal treatments.
• ... There generally are no valid alternatives to using captive animals to measure many of the emergent properties discussed by Searle et al. (2007), or, more broadly, to measure explicit fine-scale relationships among ecological site conditions, succession, vegetative states, and ungulate nutrition (Fig. 1) that are crucial for developing effective habitat management strategies and landscape planning. We do not mean to ignore certain landscape-scale tests of nutrition-explicit hypotheses (e.g., Bishop et al. 2009, Hurley et al. 2014. But such approaches often may be unsuitable for identifying finescale mechanistic relations between habitat and nutritional responses, and would have incompletely satisfied our objective of understanding ecological and successional influences on elk nutrition in our study region. ...
Article
Elk (Cervus elaphus) in the western United States are an economically and socially valuable wildlife species. They have featured species status for federal land management planning; hence, considerable modeling focused on habitat evaluation and land management planning has been undertaken for elk. The extent to which these and other habitat models for large ungulates account for influences of nutritional resources varies greatly, probably because of varying recognition of the importance of nutrition and uncertainty about how to measure and model nutrition. Our primary goals were to 1) develop greater understanding of how habitat conditions influence foraging dynamics and nutrition of elk in summer and autumn; and 2) illustrate an ecological framework for evaluating and predicting nutritional resources so that nutritional needs of elk can be integrated within landscape-scale plans, population models, and habitat evaluation models. We evaluated foraging responses of elk to clearcut logging and commercial thinning, forest succession, and season across ecological site potentials. We also identified the extent to which plant communities satisfied nutritional requirements of lactating female elk and their calves. Our study was conducted in the temperate rainforests of the Pacific Northwest on industrial and public timberlands.
• ... Mule deer (Odocoileus hemionus) are an important species in western North America. Indeed, these ungulates are a popular game species (U.S. Fish and Wildlife Service 2011;Shields et al. 2012;Monteith et al. 2013), have inherent aesthetic value for wildlife watchers (Ballard et al. 2001;Feldhamer et al. 2003), are an important prey item for carnivores (Berger and Wehausen 1991;Bleich and Taylor 1998;Forrester and Wittmer 2013) and are an integral part of the ecosystems of the western USA (Kie et al. 2002;Bishop et al. 2009). These deer have been implicated as a central component of a potential disequilibrium of predators and prey in the Great Basin, where human-induced habitat alterations during the last century are thought to have resulted in the irruption of mule deer and mountain lions (Puma concolor) (Berger and Wehausen 1991). ...
Article
ContextTranslocation of wildlife has become common practice for wildlife managers charged with management of animals on increasingly modified landscapes. Mule deer (Odocoileus hemionus) is a species of great interest to the public in western North America, and individuals of this species have been translocated several times, but little has been done to document the outcomes of those translocations. AimOur objective was to evaluate the movement, space use and site fidelity of translocated female mule deer in comparison with resident female deer in Utah, USA. Methods In January and March 2013, 102 translocated and 50 resident female mule deer were captured and fitted with radio-transmitters. Movement distances, home range sizes and seasonal range sizes were compared, as well as site fidelity between translocated and resident deer. Key resultsMean distance moved and mean annual home range size were significantly larger for translocated than resident deer in 2013, but not in 2014. Translocated deer demonstrated high site fidelity to their release areas. In total, 75% of surviving deer returned during the fall (September–November) migration to winter range within 7km of release sites. Conclusions Our results indicate that home range sizes and movements of translocated deer are larger than those of resident deer during the first year after release, but during the second year after release, home range sizes and movements of translocated deer are similar to those of resident deer. ImplicationsThe similar home range sizes and movements of translocated and resident deer >1 year after release, as well as the high site fidelity we observed, suggests that translocation is a strategy managers could use to establish or augment populations of mule deer on winter range.
• ... Similarly, pregnancy rates have been linked to nutrition and body condition [19]. In addition, body mass and condition of neonates, juveniles, and adults has been correlated with survival for caribou (Rangifer tarandus; [20]), elk [21][22], mule deer [23]), and moose [24]. ...
Article
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Forested lands in the western USA have undergone changes in management and condition that are resulting in a shift towards climax vegetation. These changes can influence the quality and quantity of forage for herbivores that rely on early-seral plants. To evaluate how management of forested landscapes might affect nutrition for Shiras moose (A. a. shirasi) at large spatial scales, we focused on shrubs and evaluated summer diet composition, forage availability, and forage quality across 21 population management units encompassing >36,000 km2 in northern Idaho, USA. We identified 17 shrub species in the diets of moose, 11 of which comprised the bulk of the diets. These forage shrubs varied markedly in both energy (mean digestible energy for leaves ranged from 9.62 to 12.89 kJ/g) and protein (mean digestible protein for leaves ranged from 1.73 to 7.90%). By adapting established field sampling methods and integrating recent advances in remote sensing analyses in a modeling framework, we predicted approximations of current and past (i.e., 1984) quantities of forage shrubs across northern Idaho. We also created a qualitative index of population trend for moose across population management units using harvest data. Predicted quantities of forage shrubs varied widely across the study area with generally higher values at more northern latitudes. The quantity of forage shrubs was estimated to have declined over the past 30 years in about half of the population management units, with the greatest declines predicted for high-energy forage species. The population trend index was correlated with the percent change in availability of moderate-energy forage shrubs, indicating that availability of forage shrubs and change in availability over time might be affecting population dynamics for moose in northern Idaho. Our study highlights the importance of assessing how changes in forest management across broad spatiotemporal extents could affect wildlife and their habitats.
• ... production, as measured by new leader growth, was nearly 1.5 times higher on North Wyoming Range (31.6 AE 2.4 mm) than Sublette (21.2 AE 2.0 mm). For large herbivores on winter range, quality of winter forage is typically low (Mautz 1978, Parker et al. 2005, Bishop et al. 2009, Korfanta et al. 2015, and availability can vary widely, making forage availability perhaps the primary constraint of winter ranges (Wallmo et al. 1977, Johnson et al. 2001). Accordingly, forage use was influenced more strongly by availability of new growth than by its quality (i.e., crude protein, PSM concentrations, and digestibility). ...
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The availability and quality of forage on the landscape constitute the foodscape within which animals make behavioral decisions to acquire food. Novel changes to the foodscape, such as human disturbance, can alter behavioral decisions that favor avoidance of perceived risk over food acquisition. Although behavioral changes and population declines often coincide with the introduction of human disturbance, the link(s) between behavior and population trajectory are difficult to elucidate. To identify a pathway by which human disturbance may affect ungulate populations, we tested the Behaviorally Mediated Forage-Loss Hypothesis, wherein behavioral avoidance is predicted to reduce use of available forage adjacent to disturbance. We used GPS collar data collected from migratory mule deer (Odocoileus hemionus) to evaluate habitat selection, movement patterns, and time-budgeting behavior in response to varying levels of forage availability and human disturbance in three different populations exposed to a gradient of energy development. Subsequently, we linked animal behavior with measured use of forage relative to human disturbance, forage availability, and quality. Mule deer avoided human disturbance at both home range and winter range scales, but showed negligible differences in vigilance rates at the site level. Use of the primary winter forage, sagebrush (Artemisia tridentata), increased as production of new annual growth increased but use decreased with proximity to disturbance. Consequently, avoidance of human disturbance prompted loss of otherwise available forage, resulting in indirect habitat loss that was 4.6-times greater than direct habitat loss from roads, well pads, and other infrastructure. The multiplicative effects of indirect habitat loss, as mediated by behavior, impaired use of the foodscape by reducing the amount of available forage for mule deer, a consequence of which may be winter ranges that support fewer animals than they did before development.
• ... Understanding the non-consumptive effects of hunting on females is important because indirect effects associated with predation risk have greater potential to affect reproductive success and survival from this segment of the population (DeCesare et al. 2014). This information is valuable for wildlife management in western North America as mule deer populations have experienced widespread declines across much of their range (Bishop et al. 2009, Bergman et al. 2015. Additionally, much of the hunting literature has focused research efforts on the targeted animals being pursued. ...
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Mule deer (Odocoileus hemionus ) are widely hunted throughout western North America and are experiencing population declines across much of their range. Consequently, understanding the direct and indirect effects of hunting is important for management of mule deer populations. Managers can influence deer mortality rates through changes in hunting season length or authorized tag numbers. Little is known, however, about how hunting can affect site fidelity patterns and subsequent habitat use and movement patterns of mule deer. Understanding these patterns is especially important for adult females because changes in behavior may influence their ability to acquire resources and ultimately affect their productivity. Between 2008 and 2013, we obtained global positioning system locations for 42 adult female deer at the Starkey Experimental Forest and Range in northeast Oregon, USA, during 5‐day control and treatment periods in which hunters were absent (pre‐hunt), present but not actively hunting (scout and post‐hunt), and actively hunting male mule deer (hunt) on the landscape. We estimated summer home ranges and 5‐day use areas during pre‐hunt and hunt periods and calculated overlap metrics across home ranges and use areas to assess site fidelity within and across years. We used step selection functions to evaluate whether female mule deer responded to human hunters by adjusting fine‐scale habitat selection and movement patterns during the hunting season compared to the pre‐hunt period. Mule deer maintained site fidelity despite disturbance by hunters with 72 ± 4% (SE) within‐year overlap between summer home ranges and hunt use areas and 54 ± 7% inter‐annual overlap among pre‐hunt use areas and 56 ± 7% among hunt use areas. Mule deer diurnal movement rates, when hunters are active on the landscape, were higher during the hunting period versus pre‐hunt or scout periods. In contrast, nocturnal movement rates, when hunters are inactive on the landscape, were similar between hunting and non‐hunting periods. Additionally, during the hunt, female mule deer hourly movements increased in areas with high greenness values, indicating that mule deer spent less time in areas with more vegetative productivity. Female mule deer maintained consistent habitat selection patterns before and during hunts, selecting areas that offered more forest canopy cover and high levels of vegetative productivity. Our results indicate that deer at Starkey are adopting behavioral strategies in response to hunters by increasing their movement rates and selecting habitat in well‐established ranges. Therefore, considering site fidelity behavior in management planning could provide important information about the spatial behavior of animals and potential energetic costs incurred, especially by non‐target animals during hunting season.
• ... For example, in the United States, predator control experiments and programs to revive declining mule deer (Odocoileus hemionus) populations have resulted from political pressure (Ballard et al. 2001). In fact, past studies have shown that deer populations may be limited by habitat quality and food (e.g., Bishop et al. 2009), and predator (coyotes, bears, felids) control was not an effective method to increase mule deer populations (Pojar and Bowden 2004;Hurley et al. 2011). When habitat change and predation interact, conservation managers are provided with the opportunity to control predation impacts through habitat management rather than predator removal, which may provide a more cost-effective management strategy (Evans 2004;Knauer et al. 2010). ...
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The implementation of mammal predator killing programs is highly controversial and deserves discussion within the scientific community. In this opinion paper, I use specific examples to discuss the whys and hows of programs aimed at: 1) ensuring human safety and health; 2) addressing concerns of interest groups; and 3) safeguarding native and endangered species. Successful programs share some commonalities: they focus on the main factor that is responsible for the problematic situation and on culprit animals, and they are developed with an understanding of the ecology and behaviour of the predators. Public support for such programs requires that killing methods be species-specific, humane, and effective. I propose a stepwise strategy to properly assess the causes of human ̶ predator conflicts and determine if a killing program should be implemented.
• ... Habitat quality, a measure of the presence of resources needed for survival and reproduction (Hall et al. 1997), can represent local conditions influencing the fitness and behavior of an individual. Reproductive success and survival of juveniles and adults can increase with habitat quality (Gaillard et al. 2000;Pettorelli et al. 2003;Bishop et al. 2009). The distribution and size of home ranges and territories also can be governed by habitat quality Mitchell and Powell 2007;Owen-Smith et al. 2010). ...
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Partial migration is a common life-history strategy among ungulates living in seasonal environments. The decision to migrate or remain on a seasonal range may be influenced strongly by access to high-quality habitat. We evaluated the influence of access to winter habitat of high quality on the probability of a female white-tailed deer (Odocoileus virginianus) migrating to a separate summer range and the effects of this decision on survival. We hypothesized that deer with home ranges of low quality in winter would have a high probability of migrating, and that survival of an individual in winter would be influenced by the quality of their home range in winter. We radiocollared 67 female white-tailed deer in 2012 and 2013 in eastern Washington, United States. We estimated home range size in winter using a kernel density estimator; we assumed the size of the home range was inversely proportional to its quality and the proportion of crop land within the home range was proportional to its quality. Odds of migrating from winter ranges increased by 3.1 per unit increase in home range size and decreased by 0.29 per unit increase in the proportion of crop land within a home range. Annual survival rate for migrants was 0.85 (SD = 0.05) and 0.84 (SD = 0.09) for residents. Our finding that an individual with a low-quality home range in winter is likely to migrate to a separate summer range accords with the hypothesis that competition for a limited amount of home ranges of high quality should result in residents having home ranges of higher quality than migrants in populations experiencing density dependence. We hypothesize that density-dependent competition for high-quality home ranges in winter may play a leading role in the selection of migration strategy by female white-tailed deer.
• ... Large, herbivorous mammals typically exhibit high and relatively stable survival rates of adults throughout their geographical range (Bishop et al., 2009;Hurley et al., 2011;Bender et al., 2012;Monteith et al., 2014). Therefore, population performance of ungulates is most often regulated by successful reproduction and recruitment of young (Gaillard et al., 1998(Gaillard et al., , 2000. ...
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Large herbivores exhibit relatively slow-paced life histories, and allocate resources toward maintaining high rates of adult survival, while juvenile survival has greater variability. Maternal females make decisions throughout life stages of reproduction to meet their nutritional demands while simultaneously ensuring survival and recruitment of young to maximize fitness. We investigated tradeoffs associated with resource selection by mule deer (Odocoileus hemionus) surrounding stages of reproduction in Mojave National Preserve, CA, United States. To understand potential tradeoffs associated with offspring survival and maternal nutritional condition, we measured differences in patterns of resource selection among pre-parturient females, females provisioning young, and females following the loss of young. The third trimester of gestation and lactation are considered the most nutritionally demanding stages of reproduction. We hypothesized that energetic costs would change rapidly throughout those stages of reproduction, especially after the loss of an offspring. Further, we hypothesized that lactating females would balance the acquisition of nutritional sources with safety of young. We used radio-collar and randomly generated locations to model resource selection in a hierarchical approach utilizing machine learning algorithms and traditional resource selection functions (RSFs). We also monitored recruitment of young born to GPS-collared females using VHF radio-collars equipped with mortality indicators. During all three stages of reproduction, adult females selected greater NDVI, less rugged terrain, areas close to water (especially while provisioning offspring), and higher elevations. Selection for greater levels of NDVI was stronger pre-parturition and following the loss of offspring compared to when females were provisioning offspring. We also observed high variation toward the selection of NDVI among individual females while provisioning young, which was less pronounced during the other reproductive stages. Offspring survival during our study was positively associated with females that selected greater levels of NDVI. Further, we were not able to detect a tradeoff between safety of young (ruggedness) and nutrient acquisition (NDVI). Perhaps predation risk and nutritional resources are not mutually exclusive in this ecosystem; and, females may be able to balance reproductive investment with the ability to select for water and nutrition while simultaneously ensuring lower risk of predation for themselves and their offspring.
• ... Furthermore, researchers could partner with federal and state wildlife agencies to monitor relationships among physiological function and demographics in free-ranging wild and domestic vertebrate herbivores. State and federal agencies often collect long-term demographic data for game species and routinely monitor body mass, survival and reproductive success of individuals (Bishop et al., 2009;De Jager and Pastor, 2009;Revermann et al., 2012;Zhao et al., 2013;Moss et al., 2014;Coates et al., 2015;DeAngelis et al., 2015;DeMay et al., 2017;Fauchald et al., 2017). These demographic parameters could be coupled with the collection of excreta from animals they handle or track to quantify biomarkers of phytochemical exposure and consequences. ...
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To understand how foraging decisions impact individual fitness of herbivores, nutritional ecologists must consider the complex in vivo dynamics of nutrient–nutrient interactions and nutrient–toxin interactions associated with foraging. Mathematical modeling has long been used to make foraging predictions (e.g. optimal foraging theory) but has largely been restricted to a single currency (e.g. energy) or using simple indices of nutrition (e.g. fecal nitrogen) without full consideration of physiologically based interactions among numerous co-ingested phytochemicals. Here, we describe a physiologically based model (PBM) that provides a mechanistic link between foraging decisions and demographic consequences. Including physiological mechanisms of absorption, digestion and metabolism of phytochemicals in PBMs allows us to estimate concentrations of ingested and interacting phytochemicals in the body. Estimated phytochemical concentrations more accurately link intake of phytochemicals to changes in individual fitness than measures of intake alone. Further, we illustrate how estimated physiological parameters can be integrated with the geometric framework of nutrition and into integral projection models and agent-based models to predict fitness and population responses of vertebrate herbivores to ingested phytochemicals. The PBMs will improve our ability to understand the foraging decisions of vertebrate herbivores and consequences of those decisions and may help identify key physiological mechanisms that underlie diet-based ecological adaptations.
• ... Unlike the thermal cover and hiding cover hypotheses, substantial evidence supports forage limitation on winter ranges. Experimental and observational research reports that nutrition on winter range can limit mule deer survival and population growth (Baker and Hobbs 1985, Peterson and Messmer 2007, Bishop et al. 2009). Suppression of forage by juniper trees may explain why the amount of pinyon pinejuniper in the annual home range was negatively related to, and explained 26% of variation in, ingesta-free body fat in female mule deer in New Mexico, USA (Bender et al. 2007). ...
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A recent paper by Coe et al. (2018) calls into question juniper removal for sagebrush obligate species based on results from a correlative study of mule deer habitat use. Our rebuttal clarifies limitations of inference in their study regarding mule deer habitat quality, highlights the importance of winter forage on demography with omitted literature, and discusses the diverse nature of the author's study area and the spatial overlap between mule deer winter range and known juniper treatments for sage‐grouse.
• ... Because nutrition effects are mediated through the mother and starvation may not be the ultimate cause of death, nutritional effects on juvenile survival are almost always more cryptic than predation (Pierce et al. 2012, Monteith et al. 2014. Lower forage availability has been shown to result in poor maternal body condition and lower juvenile survival (Shallow et al. 2015), while increased winter nutrition has been found to reduce mortality from both starvation and predation (Bishop et al. 2009). While bottom-up effects in ungulates can be cryptic, they can still be assessed in observational studies because juvenile survival and reproduction in ungulates show predictable patterns with increasing population density (Gaillard et al. 1998, Eberhardt 2002. ...
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Understanding how top–down and bottom–up effects influence population dynamics of ungulates is essential for effective management and conservation, and there is an emerging consensus that forage productivity and quality interact with predation to influence survival. From 2009 to 2013, we captured and monitored 135 neonatal black-tailed deer Odocoileus hemionus columbianus in coastal California to study possible interactions between forage and predation on survival. We estimated seasonal and annual survival rates, assessed the cause of all mortalities (n = 93), measured available forage and diet quality, estimated relative abundances of predators on summer range each year, and used remote sensing to quantify habitat types on winter range. We evaluated the relationship between fawn survival and environmental covariates with cumulative incidence and proportional hazards functions. Summer survival rates averaged 0.40 (SE = 0.05) across all years and the mean annual survival rate was 0.26 (SE = 0.04). We found that most juvenile mortality resulted from predation during summer, and spatial differences in summer survival persisted until recruitment. Variation in mortality risk from all causes was related to the birth weight of juveniles and available oak forage but not predator abundance. The risk of black bear predation, the single largest cause of mortality, was unrelated to birth weight and showed an interaction between bear abundance and the amount of oak forage. Additionally, the good body condition of adult females in spring and a lack of relationship between mortality risk and variation in deer density did not provide evidence for purely bottom–up limitation. Rather our results provide evidence that both bottom–up and top–down effects were influencing fawn survival in this declining population, and that predator identity and the timing of mortality affected the impact of predation.
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Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission.
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• Technical Report
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Letter from 55 government, independent, and academic wildlife biologists entered as public comment to the Federal Register in response to 2018 proposed rule change that will undo a 2015 Dept. of Interior rule that restricted take and methods of take of native wild mammals within national preserves in Alaska.
• Article
Mule deer (Odocoileus hemionus hemionus) populations in North America are a valuable economic wildlife resource, with the managed harvest of this species reflecting societal values and recreational opportunities in many parts of the western United States. Managing mule deer populations while allowing for harvest requires an understanding of the species’ population dynamics, including the specific factors associated with population change. We conducted a 7‐year (2005–2012) study designed to investigate habitat use and survival of mule deer in eastern Oregon, USA. We used known‐fate data for 408 adult female radio‐collared mule deer to estimate monthly survival rates and to investigate factors that might affect these rates, including seasonal distribution, temporal effects (seasonal, annual, and trends across season and year), movement behavior, and local weather and regional climatic covariates. Variation in survival rates of female mule deer was best explained by an additive effect of migration behavior, differences in survival during the fall migration period compared to the rest of the annual cycle, and precipitation levels on winter ranges of individual deer. Estimates of annual survival were higher for migrants (0.81–0.82), compared to residents (0.76–0.77). Survival was lower for migrants and residents during fall migration (Oct–Nov) and higher amounts of winter precipitation increased survival of both groups. The results of our study suggest that migrating to potentially higher quality summer foraging areas outweighed the cost of traveling through unfamiliar habitats and energy expenditure associated with migration. © 2018 The Wildlife Society.
• Article
Mule deer (Odocoileus hemionus) survival and population growth in north‐central New Mexico, USA, was previously reported to be limited by nutritional constraints due to poor forage conditions in degraded habitats. Management recommendations suggested thinning of pinyon–juniper to improve habitat quality for mule deer. To evaluate the influence of these vegetation treatments, we monitored habitat selection by 48 adult female mule deer from 2011 to 2013 in a population previously reported to be nutritionally limited. Monitoring occurred 1–4 years after completion of treatments that were intended to improve forage conditions, including mechanical reduction of pinyon pine (Pinus edulis) and juniper (Juniperus spp.) density and senescent brush (Quercus gambelii–Cercocarpus montanus) cover. During the summer season, deer selected recently treated areas, but odds ratios decreased with treatment age. However, during winter, deer avoided more recently treated areas and selected thinned areas >4 years old. Deer selected mixed oak (Quercus spp.) and pinyon–juniper savanna vegetation cover types with a moderately open canopy and ponderosa pine (Pinus ponderosa) forests while avoiding grasslands and montane shrublands across all seasons. Deer selected areas closer to water and developed areas, northeast aspects, on gentle slopes, and at lower elevations. Creating a savanna‐like cover type may elicit a positive deer response as a result of their strong avoidance of dense, closed canopy pinyon–juniper woodlands. © 2020 The Wildlife Society. We evaluated the influence of pinyon–juniper and mixed oak vegetation reduction treatments on mule deer habitat selection. During summer, deer selected recently treated areas, but odds ratios decreased with treatment age. However, during winter, deer avoided more recently treated areas and selected thinned areas >4 years old. Deer selected for a savanna‐like cover types while showing strong avoidance of dense, closed canopy pinyon–juniper woodlands.
• Article
Juvenile survival is highly variable in ungulate populations and often influences their dynamics. However, this vital rate is difficult to estimate with common wildlife management methods. Yet managers would benefit from being able to predict juvenile survival to reliably assess population dynamics for harvest management. In the case of mule deer (Odocoileus hemionus), previous studies reported that overwinter survival is the demographic parameter that influences population dynamics. We predicted winter survival of mule deer fawns under a range of habitat quality, weather, and predation regimes. We modeled overwinter survival of 2,529 fawns within 11 Population Management Units (PMU) in Idaho, 2003–2013. We used remotely sensed Normalized Difference Vegetation Index (NDVI) as a measure of summer plant productivity and both Moderate Resolution Infrared Spectroscopy Snow Data (MODIS SNOW) and the modeled Snow Data Assimilation System (SNODAS) as measures of winter snow conditions to capture spatiotemporal variation in winter survival. We used Bayesian hierarchical models to estimate survival, including covariates at the appropriate spatial and temporal resolution for each level: individual, capture site, PMU, and ecotype scales. We evaluated the predictive capacity of models using internal validation and external (out-of-sample) validation procedures comparing non-parametric Kaplan-Meier (KM) survival estimates with estimates from Bayesian hierarchical models. Statewide survival of fawns from 16 December to 1 June ranged from 0.32 to 0.71 during 2003 to 2013, with relatively low survival in 2006, 2008, and 2011 in most Game Management Units. Survival for individual PMUs ranged from 0.09 in the Weiser-McCall PMU in 2011 to 0.95 in the same PMU in 2005. Internal validation revealed models predicted KM survival well, over a range of R² from 0.78 to 0.82, with the most complex model explaining the most variance as expected. However, because our goal was to predict winter survival of mule deer in the future, we evaluated our candidate models by withholding 2 years of data and then predicted those years with each model. The best-supported predictive model was our simplest model with 3 covariates, accounting for 71% of the variance in withheld years. Forage quality in late summer-fall increased winter mule deer survival, whereas early and late winter snow cover decreased survival. At finer-spatial scales within ecotypes, our internal validation was slightly better in aspen (0.86), similar in conifer (0.80), and poorer in shrub-steppe (0.60) ecotypes than our best statewide overall survival models, which accounted for 82% of the variance. Our analyses demonstrate the generality versus precision tradeoff across ecotypes and spatial scales to understand the extent that our survival models may be applied to different landscapes with varied predator communities, climate, and plant nutrition.
• Chapter
For several decades, senescence has been considered as non-existing in free-ranging mammalian populations simply because most animals were expected to die from environmentally driven causes of mortality before the age at which senescence starts. Thanks to an increasing number of long-term individually based monitoring schemes of known-age animals in the wild, evidence of senescence in most life history traits has been reported in a large number of species across all mammalian orders. From a review of these studies, we found that actuarial senescence is the rule rather than the exception in most mammalian species studied so far.We also found clear evidence for reproductive senescence, especially in long-lived primates and ungulates, in which the oldest individuals show the existence of post-reproductive life. Senescence in life history traits is thus pervasive among mammalian species, and the key topics are now to assess the causes and consequences of senescence in mammalian population dynamics and to understand variation in the magnitude and targets of senescence among and within mammalian species. Published analyses have identified the intensity of sexual selection, the environmental context and some physiological and genetic mechanisms as major structuring factors shaping mammalian senescence within and between species. Although not yet quantified in most studies, the fitness costs of senescence do not appear as negligible as generally assumed and warrant further investigation.
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Early survival is highly variable and strongly influences observed population growth rates in most vertebrate populations. One of the major potential drivers of survival variation among juveniles is body mass. Heavy juveniles are better fed and have greater body reserves, and are thus assumed to survive better than light individuals. In spite of this, some studies have failed to detect an influence of body mass on offspring survival, questioning whether offspring body mass does indeed consistently influence juvenile survival, or whether this occurs in particular species/environments. Furthermore, the causes for variation in offspring mass are poorly understood, although maternal mass has often been reported to play a crucial role. To understand why offspring differ in body mass, and how this influences juvenile survival, we performed phylogenetically corrected meta-analyses of both the relationship between offspring body mass and offspring survival in birds and mammals and the relationship between maternal mass and offspring mass in mammals. We found strong support for an overall positive effect of offspring body mass on survival, with a more pronounced influence in mammals than in birds. An increase of one standard deviation of body mass increased the odds of offspring survival by 71% in mammals and by 44% in birds. A cost of being too fat in birds in terms of flight performance might explain why body mass is a less reliable predictor of offspring survival in birds. We then looked for moderators explaining the among-study differences reported in the intensity of this relationship. Surprisingly, sex did not influence the intensity of the offspring mass–survival relationship and phylogeny only accounted for a small proportion of observed variation in the intensity of that relationship. Among the potential factors that might affect the relationship between mass and survival in juveniles, only environmental conditions was influential in mammals. Offspring survival was most strongly influenced by body mass in captive populations and wild populations in the absence of predation. We also found support for the expected positive effect of maternal mass on offspring mass in mammals (rpearson = 0.387). As body mass is a strong predictor of early survival, we expected heavier mothers to allocate more to their offspring, leading them to be heavier and so to have a higher survival. However, none of the potential factors we tested for variation in the maternal mass–offspring mass relationship had a detectable influence. Further studies should focus on linking these two relationships to determine whether a strong effect of offspring size on early survival is associated with a high correlation coefficient between maternal mass and offspring mass.
• Chapter
In this chapter we present information collected from the population of mule deer in Mapimí, the first Biosphere Reserve in Mexico and Latin America. The reserve was decreed in 1979, covers 342,388 ha and is located at the junction of the states of Durango, Coahuila, and Chihuahua. Mule deer population dynamics data from 14 nonconsecutive years were used to analyze population density, using indirect methods such as counting fecal pellet groups, population structure by age and sex, population growth rate, and their relationship to precipitation in this arid environment. Feeding habits are presented, with mention of the main species in their diet as well as the nutrient content of the latter, diet quality was estimated by sex and age as a function of fecal nitrogen to determine if there were any differences and the relationship of habitat use and diet to sexual segregation. Data on home range and core area size are presented, as are the way in which habitat in the Chihuahuan Desert is being used by the mule deer taking the dry and rainy seasons into account, and how the risk of predation affects behavior using radiotelemetry techniques. Extensive cattle pasturing is the main economic activity in this arid zone and our data indicate that there is little overlap of habitat and little zoonosis, which is a rare occurrence between deer and cattle. The information compiled demonstrates that the population of mule deer in Mapimí is the best studied population in Mexico and should be used as a model to develop suitable strategies to improve the sustainable use of this species. The results also highlight the importance of protected areas as sources of knowledge creation and transfer.
• Thesis
Changes in landscape composition have the potential to negatively influence animal populations through shifts in dominant plant communities, loss of important forage items, or changes in structural components of habitat. In the western United States, expansion of woodland vegetation into shrub dominated communities is of concern, particularly with regard to animal populations reliant on robust sagebrush and shrub vegetation. Once established, trees can out-compete shrubs and herbaceous plants resulting in declines in abundance and diversity of shrub-forb vegetation, which female mule deer are reliant on during summer months to meet nutritional demands and to provide hiding cover for young. As a result, shifts in the distribution of pinyon-juniper woodland and increases in tree densities could negatively affect mule deer population. The study had two primary objectives, (1) to determine summer habitat composition of female mule deer in the White Mountains of California and eastern Nevada, and assess implications of pinyon-juniper expansion on habitat availability, and (2) evaluate the status of the population relative to nutritional carrying capacity and determined the influence of habitat and precipitation on demographic rates. I used mixed-effects logistic regression to model summer resource selection and demographic rates of female mule deer from 2005 to 2008. Summer resource selection was modeled at two spatial scales and among three behavioral periods, related to foraging, resting, and parturition. Summer habitat consisted of sites with high productivity, greater shrub abundance, and greater proximity to riparian areas. Deer avoided high levels of tree cover at all spatial and temporal scales, but they selected areas with low to intermediate tree cover during resting periods and during parturition. Moreover, mule deer avoided areas of productive shrub-forb vegetation (riparian and shrub NDVI), when surrounded by stands of high level pinyon-juniper cover, otherwise those vegetation types were strongly selected. During parturition female mule deer selected habitat that maximized hiding cover for newborns (greater shrub densities and structural cover), while still providing foraging opportunities (greater NDVI and shrub cover). Females underutilized certain areas that contained optimal forage such as riparian corridors, high AET sites, higher elevation shrub communities, and selected areas with low to moderate tree cover, suggesting some trade-off between minimizing predation risk for offspring, and maximizing foraging opportunities. Demographic rates (body condition, survival, fetal rates, and index of recruitment) of female mule deer were sensitive to changes in resource availability resulting from variation in precipitation or habitat composition and suggestive of a population regulated to a greater degree by bottom-up processes, and likely nearing nutritional carrying capacity. Moreover, I identified a strong negative effect of pinyon-juniper cover on annual survival, only during periods of drought, otherwise individuals were able to maintain relatively high survival regardless of habitat composition. These results suggest that in productive years mule deer are able to inhabit areas of varying levels of pinyon-juniper cover with little effect on survival, and only during the drought years are negative effects evident. Results from this study emphasize the importance of productive shrub and forb vegetation to mule deer inhabiting semi-arid regions. Maintaining areas with low-to-intermediate tree cover, where there is still abundant shrub understory and sufficient concealment cover, may be beneficial to mule deer populations. Nevertheless, the strong influence of resource availability on the population suggests that conversion of sagebrush-steppe communities into large stands of PJ dominated woodlands would likely reduce the quality and abundance of available habitat for mule deer in the Great Basin.
• Article
Advances in technology and availability associated with camera traps have resulted in a rapid rise in their use to monitor wildlife distribution, abundance, and behavior. We focus on assessing body condition, a new application of camera traps. Body condition indices must relate to the percent body fat if they are to be useful. To acquire measurements of body fat, most body condition indices require capture or mortality of animals to estimate, which has limitations when applied to free-ranging animals. We developed a non-invasive, visual body condition index (VBCI) to assess body condition of mule deer that can be applied to camera trap images or videos. The VBCI was based on the visibility of five bone regions, the scapula, spinal ridge, ribs, tuber ischium, and tuber ilium, which are covered in varying amounts of subcutaneous fat. We compared the VBCI to known values of ingesta-free body fat, obtained from ultrasonography and physical palpation of captured mule deer. Our VBCI was positively related to percent ingesta-free body fat (R2=0.23, p<0.001). Additionally, the bone regions evaluated were each correlated with the percent ingesta-free body fat. Using Spearman’s correlation, the scapula is the region most highly correlated to ingesta-free body fat (0.44, p<0.001), followed by the ischium (0.36, p<0.001), ilium (0.35, p<0.001), spinal ridge (0.31, p<0.001), and ribcage (0.12, p<0.01). Based on the relationships between VBCI and ingesta-free body fat, we developed two visual body condition indices, one that requires a broadside orientation to the camera (VBCI-1) and one that is applicable when a deer is quartered towards the camera (VBCI-2). Potential applications of the VBCI include evaluating relationships between body condition and habitat enhancements, habitat disturbances, population performances, and weather.
• Article
We examined development of 60 white-tailed deer (Odocoileus virginianus) fawns from birth to 31 days postpartum to evaluate morphometric measures for predicting neonatal age. We investigated variations in growth due to gender and maternal nutrition that might affect age prediction. Of 8 morphometric measures examined, hoof growth provided the most reliable and accurate aging model and was least affected by gender or maternal nutrition. Hoof growth was best represented by linear regression, which explained 87% of the variation and classified 74% of the fawns to within 3 days of age. Because maternal nutrition influenced body mass, chest girth, and total body length measures of fawns, aging models based on these variables should be avoided.
• Article
Plants of 3 big sagebrush subspecies, mountain big sagebrush (Artemisia tridentata ssp. vaseyana [Rydb.] Beetle), Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young), and basin big sagebrush (Artemisia tridentata Nutt. ssp. tridentata) were sampled for crude protein and acid detergent fiber (ADF) content. The ADF was determined as an indication of energy content and digestibility. Crude protein and ADF levels were compared among the 3 taxa and between lightly and heavily browsed plants and young and mature plants within each subspecies. Current year growth collected in mid-January was sampled to coincide with the season of greatest ungulate browsing on big sagebrush. Crude protein for mountain big sagebrush (8.34%) was less (P less than or equal to 0.05) than for Wyoming big sagebrush ( 11.25%) and basin big sagebrush (11.29%). All are well above the maintenance requirements of deer at 7.5% crude protein. The ADF levels between age and browse-use classes were not different (P less than or equal to 0.05) within any subspecies, although mountain big sagebrush generally had a lower ADF level than the other 2 subspecies. Wyoming big sagebrush was the only taxon with a crude protein difference ( 1.2%) (P less than or equal to 0.05) between age classes, although the difference is not biologically significant. Crude protein was not different between browse-use classes within any of the 3 taxa. Crude protein and digestibility do not indicate ungulate preference for these big sagebrush subspecies.
• Article
Samples of alligator (Juniperus deppeana), Rocky Mountain (J. scopulorum), and Utah (J. osteosperma) junipers were analyzed for volatile oil yield and terpenoid concentration. Oil yield varied (P
• Article
Two digestion-intake trials were conducted with 24 male and female white-tailed deer (Odocoileus virginianus) fawns during January, February, and March 1971. Within each trial deer were randomly assigned to one of six treatments representing a basal diet diluted with oak sawdust in levels of 0, 15, 25, 30, 35, and 45 percent. Dry matter (DM) digestibility and the digestible energy (DE) content (kcal DE/gram) were highly correlated with the percent dilution. Dry matter intake (grams/$\text{BW [kg body weight]}^{0.75}$/day) increased as digestibility decreased from a high of 3.44 kcal DE/gram to 2.17 kcal DE/gram; below this point intake decreased. Digestible energy intake (kcal $\text{DE/BW}^{0.75}$/day ± SE), on the other hand, remained relatively constant (155.2 ± 7.46) kcal above 2.17 kcal DE/gram. The data indicate that these animals were able to maintain a constant energy balance, close to the maintenance requirements of fawns, by adjusting dry matter intake when fed diets of medium to high digestibility (DE > 50 percent). Below 2.17 kcal DE/gram, energy intake decreased with the decrease in dry matter intake. The point (2.17 kcal DE/gram) representing the intersection of two regression lines for DM intake versus kcal DE/gram of feed was taken to be the threshold at which digestive tract fill began to limit the dry matter and energy intake of these animals. These results are discussed in terms of a theoretical model of the intake mechanism of ruminants.
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In large-herbivore populations, environmental variation and density dependence co-occur and have similar effects on various fitness components. Our review aims to quantify the temporal variability of fitness components and examine how that variability affects changes in population growth rates. Regardless of the source of variation, adult female survival shows little year-to-year variation [coefficient of variation (CV<10%)], fecundity of prime-aged females and yearling survival rates show moderate year-to-year variation (CV<20%), and juvenile survival and fecundity of young females show strong variation (CV>30%). Old females show senescence in both survival and reproduction. These patterns of variation are independent of differences in body mass, taxonomic group, and ecological conditions. Differences in levels of maternal care may fine-tune the temporal variation of early survival. The immature stage, despite a low relative impact on population growth rate compared with the adult stage, may be the critical component of population dynamics of large herbivores. Observed differences in temporal variation may be more important than estimated relative sensitivity or elasticity in determining the relative demographic impact of various fitness components.
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Offers an algorithm for estimating supportable densities of herbivores consuming diets at different levels of nutritional quality. This procedure is used to predict carrying capacity of burned and unburned mountain shrub habitat for mule deer Odocoileus hemionus and mountain sheep Ovis canadensis in Colorado. Unburned areas had higher carrying capacities for animals consuming low quality diets, but burned areas could support more animals on a high plane of nutrition. Traditional procedures for estimating carrying capacity failed to detect these interactions between carrying capacity and animal nutritional status. Forage amount and quality should be treated as integrated rather than distinct features of habitat.-from Authors
• Article
Forty-five white-tailed deer fawns (Odocoileus virginianus), 3 to 5 months old, were weaned and adjusted to a complete pelleted diet. They were then assigned at random to one of three dietary protein levels, from sex and weight outcome groups, for a period of 98 days. Female fawns receiving 12.7 percent crude protein gained significantly (P
• Article
Eight hand-reared white-tailed deer (Odocoileus virginianus) fawns were randomly paired and pairs were randomly assigned to 1 of 4 isocaloric diets containing 11, 15, 20, and 25 percent crude protein (dry matter basis) to study their protein requirement. Thirty-two complete digestibility, nitrogen balance, and energy balance trials were carried out. Partition of dietary energy was not significantly affected by protein level in the diet, except that proportion of energy lost in urine, presumably ketones, increased significantly (P
• Article
Investigations were conducted on the effects of essential oils of big sagebrush (Artemisia tridentata) on growth and metabolism of bacteria, including rumen microorganisms of mule deer (Odocoileus hemionus), and effects of the sagebrush feeding on appetite, rumen function, and rumen bacterial function of a fistulated steer. Sagebrush essential oils showed inhibitory action on several gram-positive and gram-negative bacteria, using the disc assay method. The addition of 0.05-ml amounts of essential oils of sagebrush inhibited the growth of deer rumen microorganisms in 9-ml amounts of agar media. The rate of cellulose digestion was decreased when 0.002-ml amounts of oils were added to 6 ml of cellulose broth and was apparently inhibited by 0.04 ml of oils. The addition of 0.1-ml amounts of oils added to 41 ml of deer rumen contents (sagebrush as substrate) decreased the rate of gas production and volatile fatty acid (VFA) concentrations. Appetite and rumen movements ceased completely following the introduction of 21 pounds of sagebrush in 7-pound daily portions through the rumen fistula of a steer.
• Article
To estimate carrying capacity of habitat for white-tailed deer (Odocoileus virginianus) it is necessary to know the energy and nutrient needs of various age-classes of deer and the value of various diet components in meeting these needs. To define energy requirements of young deer, age, weight, and intakes of digestible nitrogen and digestible or metabolizable energy from 207 balance trials were used to predict body retention of fat, protein, and energy. Caloric requirements for body energy maintenance were determined for "fall" and "winter" fawns and "summer" yearlings. Using maximum body protein or energy retention as criteria for maximum growth, caloric requirements for maintenance-plus-growth were determined in "fall" fawns and, based on protein retention only, in "summer" yearlings. This information will be useful in estimating carrying capacity.
• Article
Mule deer (Odocoileus hemionus) and elk (Cervus elaphus nelsoni) in Colorado showed a decline in post-harvest young:female ratios during 1975-1995. One hypothesized cause of this decline in productivity is a decline in male:female ratios during the breeding period. We examined Colorado Division of Wildlife (CDOW) deer and elk population composition data obtained from helicopter surveys to see whether sex ratios explained variation in young:female ratios. Data for both deer and elk supported a response of young:100 females ratios to the male:100 females ratios during the previous year. The observed ratios were about 0.25 fawns:100 does per 1 buck:100 does for deer (95% CI ± 0.14) and 0.28 calves:100 cows per 1 bull:100 cows for elk (95% CI ± 0.12). However, these effects were not adequate to explain the decline in fawn:doe (1.14 fawns:100 does per year) and calf:cow ratios (0.68 calves:100 cows per year) observed during 1975-1995. Differences in the sex ratio:productivity relationship observed between populations suggest that only some areas might show an increase in young:female ratios in response to an increase in male:female ratios, and then only a small increase in young:females was predicted. We did not detect a threshold of male:female ratios for either species that precipitated a drastic decline in productivity. Based on commonly employed population composition surveys, we conclude that increasing post-season sex ratios will have little if any impact on subsequent population productivity.
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Maintenance energy requirement of tame mule deer (Odocoileus hemionus hemionus) fawns of similar age and body weight was determined under winter conditions in north central Colorado by subjecting test groups to 4 levels of energy intake. Twenty-five digestion trials were carried out to evaluate the experimental diet in 2 winters. In the 1st winter 3 lots of fawns were used. The 1st was fed ad libitum, the second 75% and third 50% of the pretreatment ad libitum intake. In the 2nd winter one lot was fed ad libitum and another was fed 25% of ad libitum. A linear regression of metabolizable energy intake and corresponding body weight gain or loss indicated that the maintenance requirement was 158 kcal of metabolizable energy per $\text{W}_{\text{kg}}{}^{0.75}$ /day in 2 winters of study.
• Article
A generalized simulation model of energy and nitrogen balance for free-ranging nonreproducing ruminants is presented. The model estimates daily energy and nitrogen (N) requirements. Based on daily diet digestibility and N concentration, the model predicts total voluntary intake, rates of digestion and passage, partitioning of energy and N to maintenance, growth, and fattening, changes (positive or negative) in lean body mass and adipose reserves, and returns of energy and N to the ecosystem.
• Article
A captive herd of up to 92 Rocky Mountain mule deer (Odocoileus hemionus) was kept at the Denver Federal Center from 1961 through 1971. In 1967, diet supplements were increased, resulting in a substantial increase in protein consumption. Apparently associated with this improved nutrition were increases in deer weights, productivity, and antler size; earlier dates for breeding and fawning and possibly antler velvet shedding; and a decline in fawn mortality during the first week postpartum. For the 10 years of study, the mean gestation period was 203.1 days (n = 36). The mean fawn birth weight was 8.13 lb (n = 172), with singles, twins, and triplets averaging 9.10, 8.01, and 7.09 lb respectively. Males averaged 0.3 lb heavier than females, but females outnumbered males at birth (82 males: 100 females; n = 217). Regression equations for predicting fawn age were derived from body weight, hind foot length, and hoof length. In 1969-71, following increased food intake, productivity (1.92 fawns per doe) surpassed the best reported from wild mule deer herds, despite densities of 8-12 animals/acre.
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We studied the activity of 27 young white-tailed deer (Odocoileus virginianus) fawns on the Welder Wildlife Refuge in South Texas. we attached motion-sensitive radiotransmitters to 15 male and 12 female fawns, 3-12 day old,and monitored their activity for as long as 9 weeks. These fawns primarily were diurnal, although most were active for short periods once or twice a night. The amount and timing of activity of each fawn varied considerably; however, total activity increased with age as a fawn became stronger and more agile. Males were more active than females during daytime and in total at all ages, but females were more active at night. During their first two weeks of life, fawns were active an average of 8% of the time. By 1 month of age, males were active about 16% of the time, and females were active 12% of the time. The average number of daytime activity periods increased from two in fawns during their first week to five-six periods at 1 month of age. Most activity periods were less than 35 minutes long, but they increased in duration with fawn age. Two-hour activity periods were rare until fawns were more than a month old. The increase in fawn activity with age was related to the fawn's increasing ability to follow its dam, and its gradual integration into the adult deer social unit. Fawns were more active during midday hours in their first week of life, but they were most active in morning and evening thereafter.
• Article
During a 30-day grazing trial, six mule deer (Odocoileus hemionus hemionus) at pasture altered their food selection significantly as availability of forage changed. At the beginning of the trial when forbs and grasses were abundant, they comprised better than 50% of the diet; but by the end of the trial when these preferred forages were less abundant, grass and forb declined. Shrub use increased and forb and grass use decreased as snow depths increased. Results support the conjecture that big sagebrush (Artemisia tridentata wyomingensis) in excess of 30% in the diet is detrimental to mule deer nutritional health.
• Article
Mule deer (Odocoileus hemionus) were censused by 2 observers in a helicopter during 3 consecutive winters on 193 0.6475-km2 quadrats distributed, in a stratified random sampling design, throughout 1,688 km2 of pinyon-juniper (Pinus edulis-Juniperus osteosperma) winter range on the Uncompahgre Plateau, in southwestern Colorado. Quadrats were plotted on maps and aerial photos, and the 4 corners were permanently marked on the ground. Estimates of total deer population and 90% confidence limits for the 3 years were 11,401 ± 2,205, 17,884 ± 4,042, and 17,085 ± 2,951, respectively. During the 2nd and 3rd years the sample was sufficient to permit estimation of the population within 22.6 and 17.3% of the mean number of deer per 2.59 km2, respectively, with 90% confidence. Stratified random sampling reduced variance of the mean number of deer seen per 2.59 km2 by 42, 21, and 37%, respectively, relative to simple random sampling during the 3 years of the census. Procedures for conducting a census of this type and methods for minimizing observer error are detailed.
• Article
The role of density dependence in management of ungulate populations is a debated topic. I tested the effect of female removals on the yield of males in annual public hunting seasons for black-tailed deer (Odocoileus hemionus columbianus) in a 19-year study at Hopland Research and Extension Center, California. Separate treatment and control areas were not available, so pre- and posttreatment control periods were employed to examine for non-treatment effects (i.e., 6 yrs pretreatment, 7 yrs treatment, and 6 yrs posttreatment). During the treatment period, about 20 adult females/year for 3 years and 30/year for 4 years were removed. There was no difference in male harvests between pretreatment and posttreatment control periods (x̄ = 28.5 pre- and 27.3 posttreatment, P = 0.44), so the controls were pooled for testing treatment effects. Male harvest during the treatment period (x̄ = 34.9) was greater than the combined control periods (x̄ = 27.9, P = 0.02). Increased male harvest occurred despite the treatment period coinciding with a 6-year drought. Neither rainfall nor acorn (Quercus spp.) crop was related to male harvest. At the end of the treatment period, combined male harvest and female removal comprised about 21% of the estimated pre-hunt population. Males taken during the treatment period were younger and weighed less than those taken during control periods. However, 2-year-old males harvested during the treatment period had larger antlers. These results demonstrated that female harvests increased male yield apparently through lowering population density.
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We evaluated the efficacy of feeding a supplemental ration to captive and wild mule deer (Odocoileus hemionus hemionus) in Colorado. The supplement was 63% digestible and provided 2.55 kcal/g of metabolizable energy. Ad libitum intake was 28.8 g/kg BW/day. Captive animals adapted to low quality forage diets showed no digestive upsets when abruptly offered the supplemental ration ad libitum. We observed effects of feeding on animal condition and mortality in three populations of wild mule deer. Unfed deer showed the poorest body condition and highest mortality; 53% of the unfed population died during winter. Mortality rates in a population fed 0.9 kg/deer/day averaged 33%; mortality of deer fed ad libitum averaged 24%. We concluded that emergency feeding of a nutritionally adequate ration to mule deer can reduce mortality in populations subject to exceptionally severe winter weather.
• Article
Eight hand reared white-tailed deer (Odocoileus virginianus) fawns were fed a single diet, based on commercial concentrate ingredients, during five 3-week time periods (occurring in October, January, March, May, and August) to study their energy requirements. Thirty-seven complete digestibility, nitrogen balance, and indirect respiration calorimetry trials were carried out. All fawns exhibited normal growth patterns for the species. Normal reduction of voluntary dry matter intake, below maintenance, was observed during the winter. Advancing age and apparent maturation of ruminant digestive processes, as evidenced by increasing methane production, were accompanied by more efficient utilization of dietary carbohydrates, resulting in increased total digestible nutrients and net energy per unit dry matter consumed. Mean apparent maintenance metabolizable energy requirement, estimated by regression analysis of our data, over all time periods and both sexes was 154 kilocalories per kilogram body $\text{weight}^{0.75}$ and was highest in August (192) and lowest in January (109). The corresponding values across sex during periods of rapid growth (October, May, and August) and during periods of voluntary food restriction (January and March) were 173 and 125, respectively; efficiency of use of metabolizable energy for growth was substantially higher during periods of rapid growth than during the winter period. Efficiency of conversion of digestible energy to metabolizable energy was 87 percent and was not influenced by sex or season. Buck and doe fawns exhibited similar energy and protein utilization patterns over the period studied.
• Article
A drop-net, 70 × 70 ft, made of No. 60 nylon with 3½-inch mesh, was developed to capture deer in areas of high deer density. An explosive trigger device was employed, fired by pushbutton or by radio control. In a 9-month period, about 340 animals were captured, mostly white-tailed deer (Odocoileus virginianus) and axis deer (Axis axis). The average catch was 10 and the maximum was 23. The drop-net trap is highly portable, can be erected quickly, and permits individual animals to be selected for capture.
• Article
Estimates of botanical composition and nutritional quality of mule deer diets on pinyon-juniper winter range in Piceance Basin, Colorado, were based on forage selections of 8 tame animals. Diets contained nearly all browse in early winter, but browse content decreased and forbs increased as winter progressed until April when consumption of new grass growth increased sharply. Dietary crude protein levels were marginally adequate for body maintenance during much of the winter. Levels of dietary in vitro digestible dry matter were inadequate. Browse was considered critical to winter survival of deer in Piceance Basin because it was the most available forage in deep snow. Also, its nutritional value was comparable or better than that of forbs and grasses selected by deer except in April when new plant growth was available. In spite of large variation in diet compositions, deer apparently selected forage mixes to maintain a consistent, although inadequate, diet quality through the critical wintering period.
• Article
Results of in vitro digestibility trials indicate that big sagebrush (Artemisia tridentata) is a highly digestible browse for wintering mule deer. Subspecies tridentata (62.1% digested dry matter) was more highly digested than subspecies vaseyana (53.2% digested dry matter) and subspecies wyomingensis (51.4% digested dry matter). On an accession level, some accessions of big sagebrush were more highly digested than others. The accessional range was from 44.6% digested dry matter to 64.8%. No relationship was found between total monoterpenoids (essential or volatile oils) content and digestibility.
• Article
Despite its preeminence as a game species in North America, little research exists to validate nutritional condition indices for Rocky Mountain elk (Cervus elaphus nelsonii). We developed and calibrated indices of nutritional condition for live and dead Rocky Mountain elk. Live-animal indices included 20 serum and 7 urine chemistry variables, a body-condition score (BCS), thickness of subcutaneous fat and selected muscles using ultrasonography, bioelectrical impedance analysis (BIA), and body mass. Dead-animal indices included femur and mandible marrow fat, 3 kidney fat indices, and 2 carcass-scoring methods. Forty-three captive-raised cows (1.5 to 7 years old) were randomly divided into 3 seasonal groups (Sep, Dec, and Mar). Within seasonal groups, elk were fed different diets to induce a wide range of condition; all were fed identical diets 7 days prior to sampling to eliminate short-term nutritional effects. Cows were euthanized and homogenized for chemical analysis of fat, protein, water, and ash content. Estimates of fat and gross energy (GE) were compared to each condition indicator using regression, with age and season as covariates. Relations between condition and thyroxine (T4) and insulin-like growth factor (IGF-1) varied seasonally, and the relation between condition and mandible marrow fat varied among ages. Subcutaneous fat depth and BCS were most related to condition for live animals (r2 ≥ 0.87, P
• Article
Dry-matter digestibility coefficients were determined on several south-central Wyoming forage species using elk (Cervus canadensis) and steer rumen inocula. The plants collected from a site on Sheep Mountain on the south end of the Medicine Bow Range in November, January, and March were bluebunch wheatgrass (Agropyron spicatum), bluestem wheatgrass (A. smithii), Indian ricegrass (Oryzopsis hymenoides), needle-and-thread (Stipa comata), common sunflower (Helianthus annuus), antelope bitterbrush (Purshia tridentata), rubber rabbitbrush (Chrysothamnus nauseosus), and big sagebrush (Artemisia tridentata). Two-stage digestibility trials were conducted with rumen inocula from a rumen-fistulated steer and one elk, both on an alfalfa diet, and a bull elk collected from Sheep Mountain. Average digestion coefficients with the inoculum from the wild elk were grasses, 43.3 percent; common sunflower, 44.4 percent; antelope bitterbrush, 26.5 percent; rubber rabbitbrush, 41.2 percent; and big sagebrush, 53.1 percent. There were significant changes (P
• Article
The effects of weight loss during gestation on reproduction in mature cow elk (Cervus canadensis) were examined. Seven different groups of elk involving 46 cows and 36 of their calves were studied. The results indicated that weight lost during pregnancy was significantly (P < 0.01) and directly correlated to calf weights at birth and at 4 weeks of age, and to the calf growth rates through the 4th week. Elk calves that weighed more than 16 kg at birth had a 90 percent chance of surviving to 4 weeks of age under captive conditions, whereas those weighing less than 11.4 kg had less than a 50 percent chance of survival. The data indicated that cow elk that lost more than 3 percent of their body weight between January and just prior to calving did not produce 16-kg calves. When the weight of the fetus and fetal fluids and membranes just prior to parturition was subtracted from the body weight of the cow (approximately 12 percent), the total weight loss was 15 percent. Free-ranging pregnant elk required an estimated 22.7 g/kg body weight of good quality feed daily for maintenance.
• Article
Carrying capacity in plant-herbivore systems generally refers to the equilibrium density that can be attained by a herbivore. In this paper I have summarised and analysed models and methods for calculating the carrying capacity of mammalian herbivores. I examined the models for their ability to objectively and quantitatively estimate carrying capacity in deterministic and stochastic environments. Of the seven model types reviewed, only the interactive model was suitable for calculating carrying capacity in both types of environment. The interactive model relates plant biomass to the rate of increase and food intake of herbivores. The carrying capacity predictions of the model were tested using a red kangaroo-shrubland assemblage. I adjusted the degree of environmental stochasticity (rainfall) for the assemblage and modelled the resulting plant-herbivore dynamics. The results indicated that the concept of carrying capacity could be validly applied to deterministic, or low variance, environments but in stochastic environments that are characterised by a high degree of unpredictable environmental variance the concept is not useful for describing plant-herbivore dynamics.
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In a Minnesota ecosystem, mass of female white-tailed deer (Odocoileus virginianus) fawns and adults, and survival of adult females in the face of wolf (Canis lupus) predation, were directly related to maternal nutrition during gestation. Mass of single male fawns produced by 2-year-old females, and survival of yearlings to 2 years of age were related directly to the nutrition of their grandmothers.
• Article
Columbian white-tailed deer (Odocoileus virginianus leucurus, CWTD) are an endangered subspecies on which little demographic information exists. We determined survival rates and causes of mortality for 64 radiocollared adults from 1996 to 1998, and for 63 radiocollared neonatal fawns during the summer and fall months of 1996-2001 in Douglas County, Oregon, USA. Annual adult survival rates averaged 0.74 over 3 years, and most mortality (73%) occurred between fall and winter. Seasonal survival was lowest (0.75) for the fall-winter 1997-1998, and was ≥0.90 during all spring-summer periods. Annual and seasonal survival rates did not differ by gender. Average annual survival was 0.77 for deer in wildland areas compared with 0.66 for deer in suburban areas, but these differences were not consistent between years and seasons. Survival over the entire 3-year study was low (0.38). Eight deer died from a combination of emaciation and disease, and almost all (92%) necropsied deer were in poor body condition. Fawn survival to 7 months was low (0.14, 95% CI = 0.02-0.26) and declined most rapidly during the first 1.5 months of life. Predation (n = 21) and abandonment (n = 6) were the most frequent known causes of death for fawns. Our results suggest that CWTD may have responded to density-dependent factors during this short-term study, although the effects of other environmental or intrinsic factors cannot be ignored. Fawn survival may be insufficient to produce enough recruits for population growth and eventual range expansion.
• Article
Nutrient and fiber content and in vitro digestible dry matter (IVDDM) were measured in Gambel oak (Quercus gambellii) and big sagebrush (Artemisia tridentata) samples collected during January from nine geographic areas distributed widely throughout the western half of Colorado, and representing three vegetation types. Coefficients of variation among areas were less than 10% in both species in dry matter content, IVDDM and most cell and cell wall components. Variation appears to be small enough to permit application of a suitably selected, constant value, which would reflect winter nutrient content, fiber content or digestibility of these species, regardless of where collected in Colorado, in surveys where winter nutritional status of big game rangelands is being estimated for management purposes.
• Article
The breeding season of penned female white-tailed deer (Odocoileus virginianus) receiving ample nutrition during autumn was similar to that of does given approximately 30 percent less food. The mean date on which 60 deer bred was November 17 ± 8.4 days; however, 6 of 13 yearling does on inadequate rations failed to achieve estrus. Productivity of low-diet yearlings and prime-age animals amounted to 0.62 and 1.36 fawns per doe, respectively, compared to rates of 1.63 and 1.80 for high-diet deer. Males comprised 70 percent of the births from physically mature mothers on low diet when bred, whereas males constituted 46.7 percent of the offspring conceived by does on high diet. Gestation periods averaged 202.1 ± 4.1 days among 55 does provided with moderately good nutrition during pregnancy; the mean duration probably was related to the fairly large (7.5 ± 1.3 lb) fawns born. Available experimental and field evidence indicates there are four general classes of reproduction for Michigan white-tails, depending upon variations in range nutritive quality and winter weather severity; the patterns are described.
• Article
In each of 2 experiments, 6 different yearling white-tailed deer (Odocoileus virginianus) were fed 6 equicaloric concentrate diets with varying crude protein content. Maintenance requirement for protein was computed to be met by a diet containing 5.8 ± 2.0% crude protein (moisture-free basis). Each additional unit of dietary nitrogen resulted in 0.23 ± 0.01 units increase in retained body nitrogen and 0.66 ± 0.03 units increase in urinary nitrogen loss. Metabolic fecal nitrogen component was estimated to be 0.53 g/100 g dry matter consumed.
• Article
The estimation of survival distributions for animals which are radio-tagged is an important current problem for animal ecologists. Allowance must be made for censoring due to radio failure, radio loss, emigration from the study area and animals surviving p88l. :~the end of the study period. First we show that the Kaplan-Meier .procedure wid~ly used in medical and engineering studies can be applied to this problem. An example using some quail data is given for illustration. As radios maItunction -or are lost, new radio-tagged animals have to be added to the study. We show how this modification can easily be incorpor~.ted inf.<? the basic Kaplan-Meier procedure. Another example using quail data is used to illustrate the extension. We also show how the log rank test commonly used to compare two survival distributions can be generalized to allow for additions. Simple computer programs which can be run on a PC are available from the authors.
• Article
In rangehmd revegetation, selection of forages palatable to the primary grazer is crucial. Five tame mule deer were used in the spring and fall to determine forage preferences for 16 grasses commonly found on seeded foothill rangelands. Trials were con-ducted within a planted enclosure. Cheatgrass (Bromus tectorum L.) was the most preferred species in spring, and also preferred in fall. Other preferred species included 'Paiute' orchardgrass (L&c@lfi glbmerata L.), 'Luna' pubescent wheatgrass (Agropyron kichophorum link.), and fairway wheatgrass (Agropyron crista-turn [L.] Gaertn). The least preferred grasses were three species of wildrye, 'Vinall' and 'Boisoisky' Russian wildrye (Psathyrostachys juncea Fisch.) and 'Magnar' basin wildrye (Elpnus cinereus Scrib. and Men=). Results showed a wide range of preferences for grasses.
• Article
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Mule deer (Odocoileus hemionus) populations throughout the west appear to be declining, whereas white-tailed deer (Odocoileus virginianus) populations are increasing. We compared abundance, number of fetuses per female (maternity rate), recruitment, and cause-specific adult (1 year old) mortality rate for sympatric mule deer and white-tailed deer in south-central British Columbia to assess population growth for each species. White-tailed deer were three times more abundant (908 ± 152) than mule deer (336 ± 122) (mean ± 1 SE). Fetal rates of white-tailed deer (1.83) were similar to those of mule deer (1.78). There was no statistically significant difference in recruitment of white-tailed deer (56 fawns : 100 does) and mule deer (38 fawns : 100 does). The annual survival rate for adult white-tailed deer (SWT = 0.81) was significantly higher than that for mule deer (SMD = 0.72). The main cause of mortality in both populations was cougar predation. The lower mule deer survival rate could be directly linked to a higher predation rate (0.17) than for white-tailed deer (0.09). The finite growth rate () was 0.88 for mule deer and 1.02 for white-tailed deer. The disparate survival and predation rates are consistent with the apparent-competition hypothesis.Les populations de cerfs mulets (Odocoileus hemionus) semblent être en déclin dans tout l'ouest, alors que celles des cerfs de Virginie (Odocoileus virginianus) augmentent. Nous avons comparé l'abondance, le taux de production de fétus, le taux de recrutement et les taux de mortalité des adultes (1 an) attribuables à des causes spécifiques chez des cerfs mulets er des cerfs de Virginie vivant en sympatrie dans le centre sud de la Colombie-Britannique afin d'évaluer la croissance démographique de chacune de ces espèces. Les cerfs de Virginie sont trois fois plus abondants (908 ± 152) que les cerfs mulets (336 ± 122) (moyenne ± 1 erreur type). Le taux foetal est semblable chez les cerfs de Virginie (1,83) et les cerfs mulets (1,78). Il n'y a pas de différence statistiquement significative entre les taux de recrutement des cerfs de Virginie (56 faons : 100 femelles) et des cerfs-mulets (38 faons : 100 femelles). La survie annuelle des adultes est significativement plus élevée chez le cerf de Virginie (SWT = 0,81) que chez le cerf mulet (SMD = 0,72). La principale cause de mortalité chez les deux populations est la prédation exercée par les couguars. Le taux de survie plus faible du cerf mulet peut être relié directement à son taux de prédation plus élevé (0,17) que celui du cerf de Virginie (0,09). Le taux de croissance réel () est de 0,88 chez le cerf mulet et de 1,02 chez le cerf de Virginie. La disparité des taux de prédation et de survie est en accord avec l'hypothèse de la compétition apparente.[Traduit par la Rédaction]
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We evaluated transrectal ultrasonography and serum assay for detecting pregnancy in captive and wild moose (Alces a/ces). Ultrasonographic determination of twinning appeared most feasible during days 30-80 of gestation (4 November-24 December). During December, January, and March, pregnancy, but not twinning, was reliably detected ultrasonographically; diagnosis was confirmed by the presence of a fetus or placentomes. In addition, serum was assayed for pregnancy-specific protein B (PSPB). During December, January, and March, both techniques were 100% accurate in diagnosing pregnancy. However, accuracy of diagnosis during November was 95% and 90% by ultrasound and PSPB assay, respectively, based on our assumption that false positives did not occur with ultrasonography. Detection of the presence of a conceptus in utero eliminates calf detection biases associated with post-partum assessment of moose population productivity.
• Article
Nutritional stress is an important mortality factor for wintering mule deer (Odocoileus hemionus hemionus Rafinesque), particularly fawns. The rate at which fawns utilize existing fat stores is at least partially dependent upon the quality of available forage during winter. Although numerous studies have determined the nutritive value of various forage species, more research is needed to determine whether individual forage species vary in quality across the landscape. We determined whether differences existed in the nutritional quality of antelope bitterbrush (Purshia tridentata [Pursh] DC.) and cheatgrass brome (Bromus tectorum L.) among 3 winter ranges and 6 habitats within the winter ranges. In vitro dry matter digestibility (IVDMD) of bitterbrush varied among winter ranges in 1996 and 1997 (P < 0.001). The highest mean IVDMD measured on a winter range was 29.8% (n = 36, SD = 3.87) in 1997 while the lowest was 15.2% (n = 38, SD = 4.42) in 1996. Bitterbrush crude protein (CP) was different among habitats in 1997 (P = 0.005), with mean CP values ranging from 7.0% (n = 19, SD = 0.73) to 8.0% (n = 13, SD = 0.70). The length and diameter of available bitterbrush leaders varied within and among winter ranges because of differential utilization. Bitterbrush IVDMD and CP varied in relation to the mean diameter of leaders obtained from each random sampling site (P < 0.001). The quality of bitterbrush decreased as browse intensity increased. Cheatgrass IVDMD was different between winter ranges (P < 0.001) in 1996, with mean values ranging from 65.8% (n = 36, SD = 4.34) to 69.6% (n = 36, SD = 3.83). Site-specific variation should be considered when evaluating the nutritional quality of mule deer habitat, at least during winter when species diversity in deer diets is limited.