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Influence of trophy hunting and horn size on mating behavior and survivorship of mountain sheep

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Abstract

We conducted a study of the effects of horn sizes and trophy hunting on mating behavior and survival of rams in hunted and unhunted populations of Dall sheep (Ovis dalli), Rocky Mountain bighorn (O. canadensis canadensis), and desert bighorn (O. c. nelsoni) sheep. Mating success was positively correlated with horn size in Dall sheep (P = 0.03) and Rocky Mountain bighorns (P = 0.05), but not in the desert bighorn (P > 0.05) taxa. Group sizes, rams per rut group, and competition between rams were lowest in desert bighorn sheep. There were indications of greater harassment of ewes by young rams in trophy-hunted populations. In hunted populations, compared with unhunted, ewes ran away more often from approaching rams, ewes moved farther away from courting young rams (P = 0.003), younger rams performed fewer courtship displays (P = 0.042) and more aggressive displays to ewes, and sheep interacted 27% more of the time. Ram-to-ewe interaction times per individual ewe did not differ for any of the taxa (P > 0.05), and, apparently as a consequence of this, we found no discernable effects of trophy hunting on survivorship of ewes, ewe fecundity, or recruitment of young (P > 0.05). There were greater energy expenditures by young rams in the heavily hunted Dall sheep population versus the paired Dall sheep unhunted population, but not in the lightly hunted Rocky Mountain and desert bighorn populations when compared with unhunted populations. This was consistent with evidence for depressed survivorship of rams too young or too small to be hunted (approximately ages 4–6) in the heavily hunted Dall sheep population (P = 0.0001), but not in the bighorn sheep populations (P > 0.05).

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... Research on harvested populations has traditionally placed great emphasis on the demographic consequences of exploitation (e.g., Ginsberg and Milner-Gulland 1994). The hunting of large vertebrates usually leads to lower population density, a female-skewed adult sex ratio, and a younger age distribution, all of which are known to influence markedly life history traits such as body mass, reproductive allocation, and survivorship (Clutton-Brock and Lonergan 1994, Langvatn and Loison 1999, Singer and Zeigenfuss 2002, Solberg et al. 2002, Garel et al. 2006. ...
... Such changes might then have indirect effects on population dynamics, since genetic correlations may exist between the selectively targeted morphological characteristics and fitness related-traits (Hartl et al. [2003] in red deer, Cervus elaphus; Coltman et al. [2005] in bighorn sheep). Wild sheep are likely to be highly susceptible to the effects of selective hunting because (1) there is usually no limit on the maximum horn size which can be harvested (e.g., Singer andZeigenfuss 2002, Whitfield 2003), (2) horn size differences among males are very obvious to hunters, and (3) rams with fast-growing horns may become ''desirable'' as trophies before their large horns help them to achieve high reproductive success (e.g., Coltman et al. 2002), hence before they have contributed significantly in genetic terms to the next generation (Coltman et al. 2003). However, studies aimed at assessing the effect of selective hunting on animal morphology are still scarce (Festa-Bianchet 2003). ...
... Trophy hunting is a major economic activity in the Caroux-Espinouse massif, as well as in numerous other wild sheep areas (e.g., Lewis and Alpert 1997, Singer and Zeigenfuss 2002, Whitfield 2003, generating large income. However, the fee for a trophy male in our study site (e.g., from 500 € to 1300 € in 2004; G. Dalery, personal communication) remains well below fees in other European populations of mouflon (from 153 € to 7740 €; G. Dalery, personal communication). ...
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We examined the long-term effects (28 years) of habitat loss and phenotype-based selective harvest on body mass, horn size, and horn shape of mouflon (Ovis gmelini musimon) in southern France. This population has experienced habitat deterioration (loss of 50.8% of open area) since its introduction in 1956 and unrestricted selective hunting of the largest horned males since 1973. Both processes are predicted to lead to a decrease in phenotype quality by decreasing habitat quality and by reducing the reproductive contribution of individuals carrying traits that are targeted by hunters. Body mass and body size of both sexes and horn measurements of males markedly decreased (by 3.4-38.3%) in all age classes from the 1970s. Lamb body mass varied in relation to the spatiotemporal variation of habitat closure within the hunting-free reserve, suggesting that habitat closure explains part of these changes. However, the fact that there was no significant spatial variation in body mass in the early part of the study, when a decline in phenotypic quality already had occurred, provided support for the influence of selective harvesting. We also found that the allometric relationship between horn breadth and horn length changed over the study period. For a given horn length, horn breadth was lower during the second part of the study. This result, as well as changes in horn curve diameter, supports the interpretation that selective harvesting of males based on their horn configuration had evolutionary consequences for horn shape, since this phenotypic trait is less likely to be affected by changes in habitat characteristics. Moreover, males required more time (approximately four years) to develop a desirable trophy, suggesting that trophy hunting favors the reproductive contribution of animals with slow-growing horns. Managers should exploit hunters' desire for trophy males to finance management strategies which ensure a balance between the population and its environment. However, for long-term sustainable exploitation, harvest strategy should also ensure that selectively targeted males are allowed to contribute genetically to the next generations.
... 6 or 7 yr of age (Blood et al. 1970; Geist 1971; Pelletier & Festa-Bianchet 2006). Social rank, horn size, weight, age, and fighting skills determine mating success (Hogg & Forbes 1997; Coltman et al. 2002; Singer & Zeigenfuss 2002; Pelletier et al. 2004; Pelletier & Festa-Bianchet 2006); and old, mature males obtain a disproportionate number of copulations (Hogg & Forbes 1997; Coltman et al. 2002; Singer & Zeigenfuss 2002). Young male bighorns behave differently during rut when compared with older males (Geist 1968aGeist , 1971 Hogg 1984; Shackleton 1991; Hogg & Forbes 1997). ...
... 6 or 7 yr of age (Blood et al. 1970; Geist 1971; Pelletier & Festa-Bianchet 2006). Social rank, horn size, weight, age, and fighting skills determine mating success (Hogg & Forbes 1997; Coltman et al. 2002; Singer & Zeigenfuss 2002; Pelletier et al. 2004; Pelletier & Festa-Bianchet 2006); and old, mature males obtain a disproportionate number of copulations (Hogg & Forbes 1997; Coltman et al. 2002; Singer & Zeigenfuss 2002). Young male bighorns behave differently during rut when compared with older males (Geist 1968aGeist , 1971 Hogg 1984; Shackleton 1991; Hogg & Forbes 1997). ...
... Younger males also copulate later than older males that defend females (Hogg 1988). An absence of mature males might result in a less orderly and disruptive mating system, because young bighorn males may harass females excessively (Singer & Zeigenfuss 2002), potentially causing females to lose body mass (Geist 1971; Komers et al. 1999). In the absence of older conspecifics, however, young bighorn males may possess the necessary mating behaviors to successfully court and mate with females. ...
Article
Mating by young males or low male-to-female ratios can decrease pregnancy rates and postpone birthdates in ungulates, thereby hindering population growth. Young (2.5–3.5 yr old) male bighorn (Ovis canadensis) behave differently than older males, and age, horn size, mating behavior, and social rank help determine reproductive success. We estimated birthdates in two populations of bighorn sheep in Utah, USA, to determine if mating by young males or low male-to-female ratios resulted in fewer young born per female, a shift in mean timing of births, or asynchronous births. When reintroduced, the Rock Canyon population consisted of four males (two each of 2.5 yr old and 1.5 yr old) and a 1 to 7.5 ratio of males (>2 yr old) to adult females (≥3.5 yr old); the Mount Nebo population consisted of four males ≤1.5 yr old and a 0 to 12 ratio of males to adult females. For both populations, the number of young born per female did not differ between the first parturition period after reintroduction (where females were impregnated by males from their source populations) and the second period of parturition (where females were impregnated by young, reintroduced males). Mean birthdates and synchrony (SD) of births did not differ for Rock Canyon (May 12, 2001 ± 4.5 d, May 14, 2002 ± 3.2 d) or Mount Nebo (May 23, 2005 ± 8.1 d, May 22, 2006 ± 10.2 d) between the first and second years following reintroduction. Mating by young males or low male-to-female ratios had no demonstrable effect on the number of young born per female or timing and synchrony of births in these populations.
... In moose, even moderately, female-biased sex ratios (0.25-0.70) can affect the fecundity of primiparous females, although the fecundity of older females seems to be unaffected (Solberg et al. 2002 Many populations with low male-to-female ratios also tend to have a low mean male age, which may be a contributing factor to lower fecundity (Solberg et al. 2002). Nevertheless, even though it has been suggested that subadults show immature courtship behavior, are socially disruptive, and prolong the mating season (Squibb 1985;Shackleton 1991;Singer & Zeigenfuss 2002;Stalling et al. 2002), young males are nonetheless capable of achieving paternities successfully (Stevenson & Bancroft 1995;Hogg & Forbes 1997). It is less clear whether they are able to inseminate as many females as old males (Ginsberg & Milner-Gulland 1994). ...
... In addition, timing of calving in moose can be delayed when the male population is restricted to yearlings (Saether et al. 2003). Similarly, birth dates in fallow deer (Komers et al. 1999), timing of the rut in elk (Noyes et al. 1996), and median date of accepted mounts in Dall sheep (Singer & Zeigenfuss 2002) are all significantly earlier in groups or populations with mature males than when only young males are present, although other studies have shown no such effects (Table 1). Birth synchrony was greater in a moose population with an even sex ratio compared with a population in which the sex ratio was experimentally manipulated toward females (Saether et al. 2003), whereas birth dates are more synchronous with increasing male age in elk (Noyes et al. 1996) but less synchronous in fallow deer (Komers et al. 1999). ...
... Participation in rutting activities is energetically costly, and, consequently, winter survival rates of participating males are typically lower than for other individuals (Geist 1971;Stevenson & Bancroft 1995;Jorgenson et al. 1997). Subordinate males may engage in high-risk alternative mating tactics (Hogg & Forbes 1997) and may invest more heavily in reproductive activities when there is either an abundance of females relative to males or a paucity of prime-age males (Squibb 1985;Singer & Zeigenfuss 2002;Mysterud et al. 2003). One might therefore predict that young males will be more involved in the rut and suffer higher winter mortality rates in areas where heavy hunting of mature males occurs (Geist 1971;Murphy et al. 1990). ...
Article
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Selective harvesting regimes are often implemented because age and sex classes contribute differently to population dynamics and hunters show preferences associated with body size and trophy value. We reviewed the literature on how such cropping regimes affect the demography of the remaining population (here termed demographic side effects). First, we examined the implications of removing a large proportion of a specific age or sex class. Such harvesting strategies often bias the population sex ratio toward females and reduce the mean age of males, which may consequently delay birth dates, reduce birth synchrony, delay body mass development, and alter offspring sex ratios. Second, we reviewed the side effects associated with the selective removal of relatively few specific individuals, often large trophy males. Such selective harvesting can destabilize social structures and the dominance hierarchy and may cause loss of social knowledge, sexually selected infanticide, habitat changes among reproductive females, and changes in offspring sex ratio. A common feature of many of the reported mechanisms is that they ultimately depress recruitment and in some extreme cases even cause total reproductive collapse. These effects could act additively and destabilize the dynamics of populations, thus having a stronger effect on population growth rate than first anticipated. Although more experimental than observational studies reported demographic side effects, we argue that this may reflect the quite subtle mechanisms involved, which are unlikely to be detected in observational studies without rigorous monitoring regimes. We call for more detailed studies of hunted populations with marked individuals that address how the expression of these effects varies across mating systems, habitats, and with population density. Theoretical models investigating how strongly these effects influence population growth rates are also required.
... In such populations, the biased hunting pressure against mature males may lead to a female-biased adult sex ratio and a higher proportion of young males compared with non-hunted populations. In the absence of adult males, young ones may then invest more energy in rutting activities and less energy in body growth, with potential short-and long-term consequences on their body mass, size, and survival (Bon et al. 1992;Garel et al. 2006;Mysterud 2014;Singer and Zeigenfuss 2002;Stringham and Bubenik 1975; but see Monteith et al. 2020 on yearling males of white-tailed deer Odocoileus virginianus). ...
... In such populations, the biased hunting pressure against mature, old males may lead to a female-biased adult sex ratio and a higher proportion of young males compared with nonhunted populations. Where there is a lack of mature males, young ones may then invest more energy in rutting activities and less so on body growth, with potential short-and longterm consequences on their body mass, size, and survival (Bon et al. 1992;Garel et al. 2006;Mysterud 2014;Singer and Zeigenfuss 2002). The studied population of mouflon also faced trophy hunting (Garel et al. 2007), offering opportunities for young individuals to be involved in reproductive activities at similar levels to mature individuals (see Bon et al. 1992Bon et al. , 1995. ...
... However, further studies based on experimental design (e.g., Monteith et al. 2020) or on larger sample sizes comparing populations of mouflon facing high selective hunting pressures with non-hunted populations (acting as a control) would help to definitively support this hypothesis. The observed marked energetic investment of young males during the rut, while consistent with other knowledge on the influence of selective harvesting in this population (on horns size and shape; Garel et al. 2007), questioned the long-term consequences both in terms of survival and other fitnessrelated components (Festa-Bianchet et al. 2003;Forsyth et al. 2005;Garel et al. 2009;Singer and Zeigenfuss 2002;Stringham and Bubenik 1975). This result also supports the need for more empirical and comparative studies to better investigate the potential side effects of selective hunting on the rutting ecology of male ungulates (Milner et al. 2007). ...
Article
In polygynous ungulates, males invest time and energy to reproductive activities during the rut and this involvement is expected to increase with age due to different mating tactics in young versus adult males. In contrast, mating period is expected to be less costly for females for which late gestation and lactation are the most energetically demanding periods. However, empirical supports of these hypotheses through direct measures of reproductive effort are still limited in ungulate species, particularly in males. In addition, this general pattern may be modified in populations facing selective harvesting on adult males, where young males may experience less competition to mate and invest more energy during the rut. We investigated these hypotheses by studying the age- and sex-specific variations of kidney fat reserves from pre- to post-rut periods in a trophy-hunted population of Mediterranean mouflon (Ovis gmelini musimon × Ovis sp.), a polygynous dimorphic mountain ungulate. Females were found to build up energy from the pre-rut to the post-rut periods, most likely to face with the subsequent costs of gestation/lactation that occur few months later. Conversely, kidney fat mass strongly decreased similarly in both young and mature males, and with the same magnitude, suggesting a strong investment of males of all ages in this population. This might be related to the selective hunting pressure on mature males this population is facing with. This result supports the need for more empirical and comparative studies to better grasp the influence of trophy hunting on reproductive effort in male ungulates.
... In moose, there was no relationship between effort and sex ratio for either prime-aged or yearling males (Mysterud et al., 2004). Studies on dall sheep and bighorn sheep found that effort generally decreased with increasingly female-biased sex ratios (Singer & Zeigenfuss, 2002). However, sub-adult males seemed to increase their effort when adult males were scarce or absent (Singer & Zeigenfuss, 2002). ...
... Studies on dall sheep and bighorn sheep found that effort generally decreased with increasingly female-biased sex ratios (Singer & Zeigenfuss, 2002). However, sub-adult males seemed to increase their effort when adult males were scarce or absent (Singer & Zeigenfuss, 2002). Therefore, such changes in demographic structure may affect yearling, sub-adult and prime-aged males differently. ...
... females and younger males. Therefore, we propose that reproductive effort will increase for young males and decrease for prime-aged males with increasingly female biased sex ratios and a young male age structure. For yearling males, effort will likely only increase if there are also few subadult males to take over the role of prime-aged males (cf. Singer & Zeigenfuss, 2002). ...
Article
In ungulates, males and females have contrasting life histories, as usually only the females raise the young. How reproductive effort in males varies with individual level and population level characteristics has received little attention in the literature. Using published information on direct (weight loss during the rut) and indirect (rut- related changes in activity budgets, fighting frequency, etc.) measures of reproductive effort, we tested whether effort in males increased with (H1) increasing age, (H2) increasing body size, (H3) decreasing population density, (H4) increasingly female-biased sex ratio and with a younger male age structure. Consistent with H1, reproductive effort was consistently higher in prime-aged than in younger males in a large number of studies. Among younger males, sub-adult males had an equal or higher effort than yearling males. Prime-aged males had more typical rutting behaviour (e.g. roaring, tending, fighting and chasing frequencies) and they often lowered their intake of forage during the rut. However, reproductive effort usually declined for very old age classes. Reproductive effort increased with size (H2) also after accounting for age. Data on effort vs (H3) density and (H4) sex ratio/male age structure were inconclusive. Clearly, far more studies relating effort to population characteristics are needed before the rutting ecology of male ungulates can be understood.
... Dominant females where anecdotally observed surrounding available males while normally males would defend a harem of up to 30 females. While this case is extreme, changes in operational sex ratio can release sexual competition between males and change reproductive patterns (Singer and Zeigenfuss 2002). ...
... We were not able to perform these analyses here since, excepted for Châteauvillain, sampling did not cover enough years (Chizé, Chambord) with the capacity to monopolize females. Females are more available for other males to mate with, and, without big males, the competition between males decreases (Singer and Zeigenfuss 2002;Kokko and Rankin 2006). However, the number of sire per litter was no significantly influenced by Prop whether Châteauvillain was part of the analysis or not. ...
... Increase of median body mass of males means higher number of males of good quality. Good quality males are able to defend females against competitors, decreasing multiple male mating opportunity, leading to a decreased pMP(Singer and Zeigenfuss 2002;Zedrosser et al. 2007). Moreover, Nha showed a similar pattern to Medw ...
Thesis
The wild boar (Sus scrofa scrofa) is a peculiar species. It is an appreciated game species for hunters, a nightmare for farmers and a subject of debate for the society in general. The tenfold increase of the population over the last decades in France and all over Europe, despite increased hunting pressure, generated great human-wildlife conflict. The wild boar is responsible for great economic losses due to vehicle collision, diseases transmission and damaged crops and ecosystems. Improving management strategies becomes a prime interest to avoid such conflicts, or at least keep them under control. Obtaining information on the species is a first step toward good management strategies. The objective of my work is, in a first part, to characterize the mating system of the wild boar and to identify some parameters, especially hunting, influencing the reproductive processes. The second part focus on the investigation of the influence of the mating system on wild boar life history traits. My researches are based on the study of several populations contrasting in their hunting practices and on longitudinal data of a highly monitored population. The study is based on data collected on wild boars killed by hunting. Genotypes were obtained for pregnant females and their litter and paternity analyses were realized to measure the number of fathers in a litter and estimate multiple paternity rates (proportion of litter sired by more than one father). I was able to show that the mating system is mainly promiscuous (several males mate with several females) contrasting with the polygyny (a dominant male monopolizing a group of females) usually described in this species. Moreover, reproductive processes, estimated by the number of mates of a female and the multiple paternity rates, are influenced by hunting variations in a population. I also showed that number of fathers has positive effect on female fecundity. High rates of multiple paternity together with high genetic diversity were found in a heavily hunted population, suggesting multiple paternity may buffer yearly bottlenecks. However, the increase of number of fathers is not associated with increase of within-litter variation
... These deviations of population structure can have influences on various reproductive and morphological aspects like the development of animals (Singer and Zeingenfuss 2002;Mysterud et al. 2003), the fertility of females (Ginsberg and Milner-Gulland 1994), the sex ratio of foetuses (Saether et al. 2004;Holand et al. 2006) and the timing of breeding Holand et al. 2002). ...
... The increase in reproductive investment may imply energetic costs and weight loss (Yoccoz et al. 2002). For example, in bighorn sheep young males suffer higher mortality as a result of the early development of reproductive activities when adults are scarce (Singer and Zeingenfuss 2002). ...
Article
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Hunting can influence population structure with consequences in ecological and evolutionary processes. Populations of Iberian red deer (Cervus elaphus hispanicus) in Spain occur under two different management regimes: fenced and unfenced (open) estates. We compared census data, hunting bags and data from hunted individuals between both types of estates. Harvest on stags was moderate in fenced estates but strong in open ones, probably due to the competition between neighbouring landowners over the same deer populations. On the contrary, female culling was low in open estates compared to fenced ones. As a result, populations in open estates have mostly young males and strongly female-biased sex ratios. Female-biased population structure in open estates did not result in higher number of males being harvested per year compared with fenced estates, probably due to negative effects on development, survival and reproduction, and harvested males were younger, and hence, with smaller antlers. There is published evidence for undesirable effects of biased population sex ratio and age structure in these red deer populations. Our results indicate that this type of management may be unsustainable and recommend that harvest on males in open estates should be reduced and that on females increased, in order to maintain a more balanced population structure that may allow sustainable population dynamics and the operation of natural evolutionary processes.
... However, developing large weapons is energetically costly to produce and metabolically costly to carry (Picard et al. 1994(Picard et al. , 1996 and might thus involve costs in subsequent growth (Geist 1966) and survival (Reznick et al. 2000). Since large weapons are positively correlated to dominance rank and mating success in males of sexually dimorphic ungulates (Coltman et al. 2002 on bighorn sheep;Singer and Zeigenfuss 2002 in Dall sheep Ovis dalli; Preston et al. 2003;Robinson et al. 2006 in Soay sheep Ovis aries), males with rapid early growth should mate at a younger age than slowgrowing males. Mating is highly costly in males of large herbivores that are sexually dimorphic in size, involving energy demanding (e.g. ...
... If trade-offs do occur, large weapons should generate costs in future growth and survival, through physiological (Geist 1966;Picard et al. 1994Picard et al. , 1996 and social reproductive costs. Weapon size is a major determinant of dominance rank and mating success in males of large herbivores that are sexually dimorphic in size (Coltman et al. 2002;Singer and Zeigenfuss 2002;Preston et al. 2003;Robinson et al. 2006), and males with larger weapons may thus allocate in rutting activities earlier in life and in a more intense way than smaller males. As mating is costly in large herbivores, through injuries caused by fights and depletion of body reserves before winter, such allocation to mating is expected to involve investment (sensu Trivers 1972), leading males to have lower survival (Reznick et al. 2000). ...
Article
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We studied female reproductive success in two contrasting populations of Alpine Ibex: one colonizing, experiencing no density-dependence, and for which environmental conditions are consequently not limiting, the other well established, experiencing density-dependence and thus living in a limiting environment. Female body condition was better in the colonizing population than in the well-established one. As a result, reproductive success was higher in the colonizing population (80% of females reproduced each year) than in the well-established one (only 45% of females reproduced each year). We did not detect any cost of reproduction on subsequent reproduction in either of the populations, suggesting that ibex females adopt an extremely conservative reproductive tactic by limiting their reproductive effort when resource availability is reduced. However, we found a higher variance of individual reproductive success in the well-established population than in the colonizing one
... Population sex ratio may be predicted to have an effect on the level of male-male competition, but this has only been addressed to a limited extent (but see Komers et al . 1994a;Komers, Messier & Gates 1994b;Singer & Zeigenfuss 2002;Mysterud et al . 2003). ...
... Hypothesis 3. Sex ratio and male-male competition (Singer & Zeigenfuss 2002;Mysterud et al . 2003). ...
Article
1. Capital breeding is a resource use tactic common among polygynous mammals, such as many ungulates. Even though large, prime-aged males stop eating during the rutting season, younger individuals often do not and may adopt alternative mating tactics that are less strenuous. The pattern of reproductive effort is therefore probably very variable among age classes, but has rarely been quantified in male mammals. 2. Based on data of body weight of 9949 male moose (Alces alces L.) aged up to 21 years from seven populations in Norway, we tested hypotheses regarding the pattern of reproductive effort (weight loss during rut) in this capital breeder, and how this may be affected by factors such as age, population sex ratio and density. 3. Reproductive effort increased with age, even after prime-age was reached around the age of 6 years. This provides the first evidence consistent with the terminal investment hypothesis in male mammals. For the very oldest males (> 12 years) data were limited, but the tendency was that effort stabilized or even decreased slightly. Effort did not depend on the population sex ratio or density for adult males. 4. Yearling males also lost some weight during the rutting season, but this was not related to population sex ratio. Decreasing trends in yearling body weight as seen in many strongly harvested moose populations, therefore are due probably to other causes than earlier onset of rutting. Further, effort in yearlings decreased with increasing density. 5. Despite the lack of a correlation between effort and population sex ratio, a significantly faster ageing after prime-age was observed with an increasingly female-biased population sex ratio. This is consistent with the hypothesis that strongly skewed sex ratios may affect the ageing process. 6. Most ungulate populations in Europe and North America are heavily harvested or otherwise managed extensively, harvest being typically male-biased to varying degrees. The resulting skews in sex ratio provide manipulations that give unique opportunities to study life-history variation, in particular for large mammals that are otherwise difficult to manipulate. These opportunities are currently not fully utilized.
... Results of such a harvest regime include sex ratios skewed towards females and a young age structure for males (Ginsberg and Millner-Gulland 1994, Berger and Gompper 1999, Whitten 2001, Jenks et al. 2002, Keyser et al. 2006. Skewed sex ratios and a young male age structure reduces the proportion of prime-aged males, which may cause increased reproductive effort by young males and an associated reduction in their growth (Stevenson and Bancroft 1995, Laurian et al. 2000, Singer and Zeigenfuss 2002, Garel et al. 2006). ...
... Whether such declines predicate the need for a change in management strategies is uncertain. Indeed, a mean of 1.87% and 0.68% reduction in size of trophy antlers and horns, respectively, during 1950-2008 may be inconsequential relative to the benefits that accrue from recreational hunting opportunities and resultant overall benefits to conservation (Singer and Zeigenfuss 2002, Whitfield 2003, Lindsey et al. 2007, Groves and Leslie 2011, Heffelfinger 2013). The dramatic increases in entries of trophies for most categories during the last few decades (Figs. 3 and 4) also are a testament to the success of management programs for these North American species. ...
Article
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Hunting remains the cornerstone of the North American model of wildlife conservation and management. Nevertheless, research has indicated the potential for hunting to adversely influence size of horn-like structures of some ungulates. In polygynous ungulates, mating success of males is strongly correlated with body size and size of horn-like structures; consequently, sexual selection has favored the development of large horns and antlers. Horn-like structures are biologically important and are of great cultural interest, both of which highlight the need to identify long-term trends in size of those structures, and understand the underlying mechanisms responsible for such trends. We evaluated trends in horn and antler size of trophy males (individuals exhibiting exceptionally large horns or antlers) recorded from 1900 to 2008 in Records of North American Big Game, which comprised >22,000 records among 25 trophy categories encompassing the geographic extent of species occupying North America. The long-term and broad-scale nature of those data neutralized localized effects of climate and population dynamics, making it possible to detect meaningful changes in size of horn-like structures among trophy males over the past century; however, ages of individual specimens were not available, which prevented us from evaluating age-class specific changes in size. Therefore, we used a weight-of-evidence approach based on differences among trophy categories in life-history characteristics, geographic distribution, morphological attributes, and harvest regimes to discriminate among competing hypotheses for explaining long-term trends in horn and antler size of trophy ungulates, and provide directions for future research. These hypotheses were young male age structure caused by intensive harvest of males (H1), genetic change as a result of selective male harvest (H2), a sociological effect (H3), effects of climate (H4), and habitat alteration (H5). Although the number of entries per decade has increased for most trophy categories, trends in size of horn-like structures were negative and significant for 11 of 17 antlered categories and 3 of 8 horned categories. Mean predicted declines during 1950–2008 were 1.87% and 0.68% for categories of trophy antlers and horns, respectively. Our results were not consistent with a sociological effect (H3), nutritional limitation imposed by climate (H4), or habitat alteration (H5) as potential explanations for long-term trends in size of trophies. In contrast, our results were consistent with a harvest-based explanation. Two of the 3 species that experienced the most conservative harvest regimes in North America (i.e., bighorn sheep [Ovis canadensis] and bison [Bison bison]) did not exhibit a significant, long-term trend in horn size. In addition, horn size of pronghorn (Antilocapra americana), which are capable of attaining peak horn size by 2–3 years of age, increased significantly over the past century. Both of those results provide support for the intensive-harvest hypothesis, which predicts that harvest of males has gradually shifted age structure towards younger, and thus smaller, males. The absence of a significant trend for mountain goats (Oreamnos americanus), which are difficult to accurately judge size of horns in the field, provided some support for the selective-harvest hypothesis. One other prediction that followed from the selective-harvest hypothesis was not supported; horned game were not more susceptible to reductions in size. A harvest-induced reduction in age structure can increase the number of males that are harvested prior to attaining peak horn or antler size, whereas genetic change imposed by selective harvest may be less likely to occur in free-ranging populations when other factors, such as age and nutrition, can override genetic potential for size. Long-term trends in the size of trophy horn-like structures provide the incentive to evaluate the appropriateness of the current harvest paradigm, wherein harvest is focused largely on males; although the lack of information on age of specimens prevented us from rigorously differentiating among causal mechanisms. Disentangling potential mechanisms underpinning long-term trends in horn and antler size is a daunting task, but one that is worthy of additional research focused on elucidating the relative influence of nutrition and effects (both demographic and genetic) of harvest.
... In addition, adjustments of male mating tactics related to changes in sex ratio may occur in relation to male age (bison Bison bison: Komers, Messier & Gates, 1994; moose Alces alces: Solberg & Saether, 1994). Indeed males can reproduce as yearlings (Hogg & Forbs, 1997; Coltman et al., 2002), with a lower risk-to-reward ratio when the sex ratio is female biased (Soay sheep Ovis aries: Stevenson & Bancroft, 1995) or when adult males are rare (Squibb, 1985; Singer & Zeigenfuss, 2002). To reproduce as sub-adults, however, may still bear some costs, e.g. ...
... To reproduce as sub-adults, however, may still bear some costs, e.g. young bighorn rams Ovis canadensis suffer a higher mortality rate as a consequence of early reproductive activities, when adult rams are scarce (Singer & Zeigenfuss, 2002). One can thus expect a higher investment by sub-adults in reproductive activities either when females are in excess relative to males or when there is a paucity of adult males. ...
Article
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The relationships among harem size, adult sex ratio (proportion of males > 5 years in the adult population, i.e. males > 5 years plus females > 2 years) and male age-structure of red deer Cervus elaphus were investigated in La Petite Pierre National Reserve (PPNR) in France. We tested whether: (1) increasing adult sex ratio leads to a decrease in harem size along with an increase in the number of harems within a given rut period; (2) whether participation of sub-adult males in mating activities increases with decreasing adult sex ratio, and as the proportion of adult males decreases. Harem size did not vary over the mating period, suggesting a high turnover of harem-holders leading to an increase in the costs of mating for males. Harem size averaged 1.43 ± 0.91 and was lower than harem sizes typically reported for red deer (e.g. > 2.5 in Scotland and Norway). In support of the first prediction, a decrease in harem size and an increase in the total number of harems seen with an increasing sex ratio was observed (harem size = 2.08 – 1.26 [±0.43] ± (sex ratio); r2= 0.25, F1,18= 6.19, P= 0.02). Both the uniform distribution of females among harem stags and the small harem sizes observed in PPNR might concur to a smaller variance in male reproductive success than previously reported in red deer. Lastly, in partial support of the second prediction, the proportion of sub-adult males observed during the mating season decreased with increasing adult sex ratio and with increasing proportions of adult males. Whether or not the lower proportion of sub-adults seen when competition among mature males increases means that fewer young males mate cannot be assessed from our study.
... However, developing large weapons is energetically costly to produce and metabolically costly to carry (Picard et al. 1994(Picard et al. , 1996 and might thus involve costs in subsequent growth (Geist 1966) and survival (Reznick et al. 2000). Since large weapons are positively correlated to dominance rank and mating success in males of sexually dimorphic ungulates (Coltman et al. 2002 on bighorn sheep;Singer and Zeigenfuss 2002 in Dall sheep Ovis dalli; Preston et al. 2003;Robinson et al. 2006 in Soay sheep Ovis aries), males with rapid early growth should mate at a younger age than slowgrowing males. Mating is highly costly in males of large herbivores that are sexually dimorphic in size, involving energy demanding (e.g. ...
... If trade-offs do occur, large weapons should generate costs in future growth and survival, through physiological (Geist 1966;Picard et al. 1994Picard et al. , 1996 and social reproductive costs. Weapon size is a major determinant of dominance rank and mating success in males of large herbivores that are sexually dimorphic in size (Coltman et al. 2002;Singer and Zeigenfuss 2002;Preston et al. 2003;Robinson et al. 2006), and males with larger weapons may thus allocate in rutting activities earlier in life and in a more intense way than smaller males. As mating is costly in large herbivores, through injuries caused by fights and depletion of body reserves before winter, such allocation to mating is expected to involve investment (sensu Trivers 1972), leading males to have lower survival (Reznick et al. 2000). ...
Article
Large horns or antlers require a high energy allocation to produce and carry both physiological and social reproductive costs. Following the principle of energy allocation that implies trade-offs among fitness components, growing large weapons early in life should thus reduce future growth and survival. Evidence for such costs is ambiguous, however, partly because individual heterogeneity can counterbalance trade-offs. Individuals with larger horns or antlers may be of better quality and thus have a greater capacity to survive. We investigated trade-offs between male early horn growth and future horn growth, baseline mortality, onset of actuarial senescence, and rate of ageing in an Alpine ibex (Capra ibex ibex) population. Horn growth of males in early life was positively correlated to their horn length throughout their entire life. Cohort variation and individual heterogeneity both accounted for among-individual variation in horn length, suggesting both long-lasting effects of early life conditions and individual-specific horn growth trajectories. Early horn growth did not influence annual survival until 12 years of age, indicating that males do not invest in horn growth at survival costs over most of their lifetime. However, males with fast-growing horns early in life tended to have lower survival at very old ages. Individual heterogeneity, along with the particular life-history tactic of male ibex (weak participation to the rut until an old age after which they burn out in high mating investment), are likely to explain why the expected trade-off between horn growth and survival does not show up, at least until very old ages.
... The absence of large male bison resulted in more sexual and aggressive interactions by younger males and excessive harassment of females (Komers et al. 1994). Such harassment of females by young males may have negative consequences for reproductive females, as reported in other ruminants (Singer & Zeigenfuss 2002). Consequently, there are potential benefits to females that mate with large males. ...
Article
We studied group size, composition, and mating activities in American bison (Bison bison) during rut on the Delta Junction Bison Range in interior Alaska, USA, in 1996 and 1997. Our purpose was to determine the effects of large males (≥5 yr old) on mating and associated activities. Groups with large males were larger than those containing smaller males. Most groups of bison were mixed-sex (90%), but large males occurred in only one-half of all groups. Moreover, females in groups with large males were more likely to copulate than those in groups with smaller males, indicating a female preference for large males. Nevertheless, our results are consistent with large males seeking out adult females for mating rather than vice versa. Mating peaked in mid-August during both the study years and was highly synchronous. Scent marking was coincident with mating, an outcome consistent with a hypothesis of such behavior triggering ovulation. Scent marking by large male bison occurred in both male–male and male–female contexts, but was associated most often with sexual activities. No differences in group size occurred with changes in weather or among vegetation types occupied by bison. Group size of bison, however, was larger with increasing distance from the forest edge, which likely was a response to predation risk in this predator-rich environment.
... Yearling male weight, but not female weight, was more closely (negatively) correlated with sex ratio than density, suggesting that decline in weight of yearling males was the result of increased rutting behaviour when few older males were present (Solberg et al., 1994). However, studies on dall sheep Ovis dalli and bighorn sheep found decreased effort for adults with increasingly female-biased sex ratios (Singer & Zeigenfuss, 2002). Effort of yearling males did not vary according to population density during the rutting season in our study. ...
Article
In sexually dimorphic ungulates, male reproductive success depends on fighting with other males for access to females during a brief rutting season. Large body size is necessary for success in intrasexual competition, and a few large-sized males are often able to monopolize access to female groups. Earlier studies have reported that reproductive effort increases with age until prime-age is reached, and one study that population density lowered effort in (older) males. No study has directly assessed whether there is within-age-class variation in effort resulting from varying levels of intra-male competition. It is reported here the weight loss during the rutting season of 54 individual male reindeer Rangifer tarandus coming from eight herds with varying density (3.3–6.0 deer/km2) and sex ratio (4–28% males). In agreement with earlier studies, reproductive effort was lower for young (1- to 2-year-old) than for prime-aged (3- to 5-year-old) males both on an absolute and relative scale. Among 1-year-old males (n=33), effort was lower as sex ratio became closer to even, but density during the rutting season had no effect. This suggests that yearling males take a more active role when prime-aged males are absent. In addition to the insight into male ungulate life history, understanding male rutting behaviour may also have implications for population dynamics.
... For example, trophy-sized male walrus, the object of sport hunts, may be a different stock than the part of the same population that supports the subsistence hunt in the same area. Trophies are selected on the basis of absolute size, and as long as the number of big males removed does not reduce the productivity of the population (surplus male hypothesis, but see Harris et al., 2002;Singer and Zeigenfuss, 2002), the number of animals available for subsistence hunting will not change. The edible walrus products of trophy-kills return to the subsistence consumers, so the sport hunt is not considered additive. ...
Article
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Defining management units is basic to the sound management of resources. Walrus (Odobenus rosmarus rosmarus) are hunted throughout their range in Canada and are subject to other human activities requiring management decisions. Current management units are based on a comprehensive review and a stock assessment completed in the mid 1990s. Between 1993 and 2004, satellite-linked radio tags provided information on the movements of walrus in Canada's High Arctic. These data were incorporated with other information that has become available since 1995 to reassess walrus management units in Canada. Tagging data and other information suggest that some finer discrimination of walrus populations is needed as a precautionary approach and to formulate testable hypotheses. Specifically, the previous North Water/Baffin Bay walrus stock may be considered to be three stocks: Baffin Bay, west Jones Sound, and Penny Strait-Lancaster Sound stocks. The Foxe Basin population appears to comprise two stocks (North Foxe Basin and Central Foxe Basin) rather than one. Previously suspected subdivisions in the Hudson Bay-Davis Strait population are substantiated by isotopic evidence although sampling on a finer geographic scale is required before this stock can be partitioned. There is new evidence to support the previously postulated separation of the walrus in the Southern and Eastern Hudson Bay stock from all others, but no evidence to warrant subdivision.
... Presanella, 29.562%; Brenta, 25.261.6%). Hunting has been known to influence a range of life history traits, including survival, mating behaviour and body mass [46,47]. Where hunting pressure is higher, and risk of mortality is greater, it could pay to allocate more energy to reproduction earlier in life. ...
Article
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A fundamental life history question is how individuals should allocate resources to reproduction optimally over time (reproductive allocation). The reproductive restraint hypothesis predicts that reproductive effort (RE; the allocation of resources to current reproduction) should peak at prime-age, whilst the terminal investment hypothesis predicts that individuals should continue to invest more resources in reproduction throughout life, owing to an ever-decreasing residual reproductive value. There is evidence supporting both hypotheses in the scientific literature. We used an uncommonly large, 38 year dataset on Alpine chamois (Rupicapra rupicapra) shot at various times during the rutting period to test these two hypotheses. We assumed that body mass loss in rutting males was strongly related to RE and, using a process-based approach, modelled how male relative mass loss rates varied with age. For different regions of our study area, we provide evidence consistent with different hypotheses for reproductive allocation. In sites where RE declined in older age, this appears to be strongly linked to declining body condition in old males. In this species, terminal investment may only occur in areas with lower rates of body mass senescence. Our results show that patterns of reproductive allocation may be more plastic than previously thought. It appears that there is a continuum from downturns in RE at old age to terminal investment that can be manifest, even across adjacent populations. Our work identifies uncertainty in the relationship between reproductive restraint and a lack of competitive ability in older life (driven by body mass senescence); both could explain a decline in RE in old age and may be hard to disentangle in empirical data. We discuss a number of environmental and anthropogenic factors which could influence reproductive life histories, underlining that life history patterns should not be generalised across different populations.
... Thus, the dominance of males with a correct development of the horns plays a determinant role in natural selection of genetically stable populations (Maylon and Healy, 1994). Relevance of a good horn development in the sexual activity is evident because mating success is positively correlated with horn size in many species of wild sheep such us Dall sheep (Ovis dalli) and Rocky Mountain bighorns (Ovis canadensis canadensis) (Singer and Zeigenfuss, 2002). ...
Article
Annual variations in the growth of horns, and their correlation with seasonal changes of testicular size, and prolactin (PRL) and melatonin secretion were monitored in six pubertal mouflon rams living in their original latitude (40 degrees N). Mouflons born and maintained under captive conditions were classified in two age classes: sub-adult (2 years; n=3) and adult (> or =3 years; n=3). The rate of horn growth was greater (P <0.001) in sub-adult than in adult mouflon rams. Horn growth was influenced by season in both adult and sub-adult mouflons (P <0.05) with largest monthly growth occurring in spring and summer. Seasonal variations of plasma PRL concentrations were correlated with horn growth in adult, but not in sub-adult mouflon rams. The rate of horn growth was inversely correlated with testicular size (r=-0.5, P=0.07). Seasonal changes in the amplitude of the daily melatonin rhythm in solstices and equinoxes were observed, which were not correlated with variations in the rate of horn growth. These results provide support for a possible role of PRL in the control of growth of horns in the adult mouflon.
... Horn size in mountain ungulates has important and diverse implications for conservation biology and evolution (Coltman et al. 2002, Singer & Zeigenfuss 2002. Horn size signals individual quality (von Hardenberg et al. 2007) and reflects the environmental conditions experienced both during early development , Toı¨go et al. 1999 and throughout an animal's entire life, especially in species where substantial horn growth continues throughout life. ...
Article
Horn growth in the Caprinae is affected by several factors including age and nutrition, and analysis of annual horn increments can be used to interpret past events. We documented patterns of horn growth in male alpine ibexes (Capra ibex ibex) in the central European Alps and analyzed relationships between annual horn increments, weather, and plant phenology in 2 different climatic regions during 1981-1990. Age accounted for 50% of total variance in horn growth in male alpine ibexes 1-6 years of age. Horn growth differed among climatic regions and calendar years. In years with early onset of vegetation growth, horn growth was enhanced uniformly over all age classes in both climatic regions. Horn growth was a function of ambient temperature during March-May and of plant phenology in spring, implicating onset of growth of vegetation and availability of food resources. Duration of growth of vegetation was assumed to be directly related to date of vegetation onset, but further studies are necessary to test this hypothesis.
... It is therefore not surprising that these highly successful males have the highest chance of being shot during the rut, as they spend more time in rutting activities that not only make them more predictable in terms of use of space, but also more conspicuous (by, for example, roaring, fighting or courting). The consequences of shooting prime males in ungulate populations -with the resultant increase in access to females of less fit males -are widely known (Coltman et al., 2003) and range from an overall reduction of population viability (Mysterud et al., 2005) to a decrease in weight and/or horn or antler size in males (Singer and Zeigenfuss, 2002;Coltman et al., 2003). ...
... The main difference between the two types of estates is that in fenced areas managers can maintain sex ratio equilibrium and age structure of the population, including mature stags, whereas in open areas hunting pressure from neighbouring estates affects the whole population, leading to strongly female biased sex ratios and age structures which are heavily skewed towards younger males (Carranza 1999; see also ). Contrasting sex ratios and population structure between fenced and open estates are likely to affect male growth and antler development (Singer & Zeingenfuss 2002, Yoccoz et al. 2002, Mysterud et al. 2003, although this issue deserves further research. ...
Article
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Hunting management of red deer Cervus elaphus populations may tend to increase population densities to maximise annual yield. Some studies have shown that density and low winter temperatures affect red deer populations in central and northern Europe, but these results cannot be extrapolated to red deer populations in the Mediterranean region where the limiting season is summer instead of winter. The two regions are predicted to experience different climate change effects: while rainfall may increase in northern latitudes, heavier droughts are expected in the Mediterranean region. We studied red deer populations of different densities on 19 hunting estates in southern Spain during two years with contrasting precipitation levels. Our aim was to quantify the combined effects of drought and population density on the development of stags, which is the main economic objective of hunting management in these areas. We found that drought affected body and antler size negatively, and that the effects were more severe in populations of high density. On the basis of our results, we recommend reducing the current densities of red deer in southern Spain to maintain the economic and environmental sustainability of hunting exploitation in the context of global climate change.
... In polygynous mating systems typical of sexually dimorphic cervids (Geist 1966, Ralls 1977, Weckerly 1998, Loison et al. 1999), dominant males often limit mating opportunities of younger, smaller males (Hirth 1977, Bowyer 1986, Van Ballenberghe & Miquelle 1996). In the absence of old, large males, the age at which males mate decreases (McCullough 1982, Strickland et al. 2001, Jenks et al. 2002, Singer & Zeigenfuss 2002). An earlier age of mating may result in younger males making large investments in antler development and size (Mysterud et al. 2003). ...
Article
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Moose Alces alces gigas in Alaska, USA, exhibit extreme sexual dimorphism, with adult males possessing large, elaborate antlers. Antler size and conformation are influenced by age, nutrition and genetics, and these bony structures serve to establish social rank and affect mating success. Population density, combined with anthropogenic effects such as harvest, is thought to influence antler size. Antler size increased as densities of moose decreased, ostensibly a density-dependent response related to enhanced nutrition at low densities. The vegetation type where moose were harvested also affected antler size, with the largest-antlered males occupying more open habitats. Hunts with guides occurred in areas with low moose density, minimized hunter interference and increased rates of success. Such hunts harvested moose with larger antler spreads than did non-guided hunts. Knowledge and abilities allowed guides to satisfy demands of trophy hunters, who are an integral part of the Alaskan economy. Heavy harvest by humans was also associated with decreased antler size of moose, probably via a downward shift in the age structure of the population resulting in younger males with smaller antlers. Nevertheless, density-dependence was more influential than effects of harvest on age structure in determining antler size of male moose. Indeed, antlers are likely under strong sexual selection, but we demonstrate that resource availability influenced the distribution of these sexually selected characters across the landscape. We argue that understanding population density in relation to carrying capacity (K) and the age structure of males is necessary to interpret potential consequences of harvest on the genetics of moose and other large herbivores. Our results provide researchers and managers with a better understanding of variables that affect the physical condition, antler size, and perhaps the genetic composition of populations, which may be useful in managing and modelling moose populations.
... When interpreting our results we caution that regional or population-specific differences between bighorn and thinhorn sheep (e.g. Singer & Zeigenfuss, 2002) could still lead to differing selection regimes. Thus it may be possible that the assumption that rapid growth results in increased longevity (Coltman et al., 2003(Coltman et al., , 2005 in unhunted populations is valid for bighorn sheep, although the earlier work of Geist (1966aGeist ( , 1971) may suggest otherwise. ...
Article
We used horn measurements from natural and hunted mortalities of male thinhorn sheep Ovis dalli from Yukon Territory, Canada, to examine the relationship between rapid growth early in life and longevity. We found that rapid growth was associated with reduced longevity for sheep aged 5 years and older for both the hunted and natural mortality data sets. The negative relationship between growth rate and longevity in hunted sheep can at least partially be explained by morphologically biased hunting regulations. The same trend was evident from natural mortalities from populations that were not hunted or underwent very limited hunting, suggesting a naturally imposed mortality cost directly or indirectly associated with rapid growth. Age and growth rate were both positively associated with horn size at death for both data sets, however of the two growth rate appeared to be a better predictor. Large horn size can be achieved both by individuals that grow horns rapidly and by those that have greater longevity, and the trade-off between growth rate and longevity could limit horn size evolution in this species. The similarity in the relationship between growth rate and longevity for hunted and natural mortalities suggests that horn growth rate should not respond to artificial selection. Our study highlights the need for the existence and study of protected populations to properly assess the impacts of selective harvesting.
... Horn size in mountain ungulates has important and diverse implications for conservation biology and evolution (Coltman et al. 2002, Singer & Zeigenfuss 2002). Horn size signals individual quality (von Hardenberg et al. 2007) and reflects the environmental conditions experienced both during early development (Coˆteét al. 1998, Toı¨go et al. 1999) and throughout an animal's entire life, especially in species where substantial horn growth continues throughout life. ...
Article
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Factors affecting horn size in wild Caprinae are of biological and socio-economic interest because several species are selectively harvested on the basis of this heritable character. We analysed temporal trends in horn size in two mountain ungulates from south-eastern Spain, the Iberian wild goat Capra pyrenaica and the aoudad Ammotragus lervia. Trophy harvest is the main way in which these two species are exploited, although ‘poor-quality’ aoudads are also selectively removed. In recent years, both populations have suffered drastic decreases in number due to outbreaks of sarcoptic mange that led to the suspension of hunting for several years. Horn length in harvested male wild goats and aoudads declined during our study period. Over an 18-year period, the mean age of male goats shot as trophies rose by four years, while the age of trophy-harvested aoudads decreased by around six months over a 9-year period. Age and environmental conditions during the first few years of life explained 20% of variance in horn size in Iberian wild goat and 53% in aoudad. Population density early in life explained much of the reduction in goat horn size over time. Nevertheless, the major fall in population densities after the sarcoptic mange outbreaks did not lead to a recovery in horn size in either species. We suggest that the selective removal of large-horned animals may contribute to a decline in horn size. Other factors that may also explain the observed pattern include changes in interspecific competition, long-lasting maternal effects and reduced carrying capacity due to overgrazing during high density periods. Unfortunately, our data sets did not allow us to account for the possible effects of these factors.
... During the peak breeding season, when female receptivity is at its highest, malemale competition can be intense, and breeding can be monopolized by a small number of dominant males (Clutton-Brock et al. 1985). Young males are known to increase their reproductive effort (RE; allocation of resources to current reproduction) in years when older males are scarcer (Singer and Zeigenfuss 2002). This might also hold true within a season if older males exhaust their energy stores and cease to compete effectively before the end of the period of female receptivity. ...
Article
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Abstract Age-dependent reproductive timing has been observed in females of a number of species; older females often breed earlier in the season and experience higher reproductive success as a result. However, to date, evidence for within-season variation in reproductive effort (RE) for males has been relatively weak. Males are expected to time RE in light of intraseasonal variations in the availability of receptive females and competition with other males. Young males, which are typically smaller and less experienced, might benefit from breeding later in the season, when male-male competition is less intense. Using a long-term data set of Alpine chamois Rupicapra rupicapra, we sought to evaluate the hypothesis that younger males allocate highest RE late in the breeding season, at a time when older male RE has decreased substantially. Our results support this hypothesis, which suggests that intraseasonal variation in RE may be an adaptive life-history trait for males as well as females.
... In polygynous mating systems typical of sexually dimorphic cervids (Geist 1966, Ralls 1977, Weckerly 1998, dominant males often limit mating opportunities of younger, smaller males (Hirth 1977, Bowyer 1986, Van Ballenberghe and Miquelle 1996. In the absence of old, large males, the age at which males mate decreases (McCullough 1982, Strickland et al. 2001, Jenks et al. 2002, Singer and Zeigenfuss 2002. An earlier age of mating may result in younger males making large investments in antler development and size (Mysterud et al. 2003). ...
... Crowe and Liversidge (1977) tested and confirmed Bigalke's (1970) hypothesis, but identified young adult males (19-30 months) as succumbing rather than juvenile males (-12 months). A similar skewed sex ratio in favour of females related to elevated male mortality occurs in species as varied as Springbok (Bednekoff and Ritter 1997) and Mountain Sheep Ovis canadensis Shaw, 1804 (Singer and Zeigenfuss 2002). ...
Article
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The sex ratio of a population of Arabian Sand Gazelle in Mahazat as-Sayd Protected Area in central western Saudi Arabia was compared to that determined from 296 skulls collected from the same area. Skulls were collected between March 2008 and March 2009 during a period of mass die-off caused by a severe drought. Most abundant were male skulls ageing between 18 and 24 months. The skulls of natural mortalities indicated an imbalanced sex ratio skewed towards males (1.39:1), compared to a sex ratio slightly skewed towards adult females (1:1.07) in the living population. Horn lengths of males and females were significantly shorter in the wild population of Mahazat as-Sayd than compared to an analogous population in captivity (King Khalid Wildlife Research Centre, KKWRC, Saudi Arabia). Possible causes for diverging sex ratio were linked to increased male mortality during the drought. Male mortalities and female biased sex ratio are discussed in the light of territoriality, predation, poor environmental conditions and limited opportunities to migrate.
... For example, trophy-sized male walrus, the object of sport hunts, may be a different stock than the part of the same population that supports the subsistence hunt in the same area. Trophies are selected on the basis of absolute size, and as long as the number of big males removed does not reduce the productivity of the population (surplus male hypothesis, but see Harris et al., 2002;Singer and Zeigenfuss, 2002), the number of animals available for subsistence hunting will not change. The edible walrus products of trophy-kills return to the subsistence consumers, so the sport hunt is not considered additive. ...
... Dominant males with the best developed horns are, therefore, naturally selected as herd sires. The importance of appropriate horn development in sexual activity is also made manifest in that mating success is correlated with horn size in many wild ruminant species, such as Dall sheep (Ovis dalli dalli; see Singer and Zeigenfuss 2002) and Rocky Mountain bighorn sheep (Ovis canadensis canadensis; see Coltman et al. 2002). Moreover, it has been shown that horn quality (size and symmetry ) is associated with sperm motility (). ...
Article
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Studies on seasonal horn development and the endocrine mechanism regulating its pattern in wild ruminants are scarce. The aim of this paper was to study the influence of photoperiod and prolactin (PRL) on horn growth in two wild ruminant species: the European mouflon and the Iberian ibex. Eighteen male ibexes and 13 mouflon rams, maintained in captivity, were divided into three groups: a control group, kept under a natural photoperiod (latitude, 40°25′ N); a long-day group, exposed to an artificial photoperiod of 15-h light and 9-h darkness; and a group treated with bromocriptine (BCR; 10 mg twice weekly during spring and summer) to induce hypoprolactinaemia. Horn length growth (HLG) was recorded weekly for 18 months; plasma PRL concentrations were measured twice monthly by radioimmunoassay. In the ibexes of the long-day group, the period of strong horn development during spring–summer was significantly reduced by 2 months compared with the controls. In the mouflons of the long-day group, this same period was significantly increased by 9 months. In the BCR-treated animals, hypoprolactinaemia was observed in both species, but HLG was the same as in the corresponding controls. The present results suggest that the seasonal pattern of horn growth of wild ruminants is primarily modulated by photoperiod in a species-dependent manner. The persistence of resurgence of horn growth during spring in the BCR-induced hypoprolactinaemic animals of both species suggests that annual variations in blood PRL concentration have no effect on seasonal variation in horn growth.
... Dominant males with the best developed horns are, therefore, naturally selected as herd sires. The importance of appropriate horn development in sexual activity is also made manifest in that mating success is correlated with horn size in many wild ruminant species, such as Dall sheep (Ovis dalli dalli; see Singer and Zeigenfuss 2002) and Rocky Mountain bighorn sheep (Ovis canadensis canadensis; see Coltman et al. 2002). Moreover, it has been shown that horn quality (size and symmetry ) is associated with sperm motility (). ...
... Males with greater horn growth obtain high-quality resources, are more resistant to parasites (Luzón et al., 2008) and have better sperm quality (Santiago-Moreno et al., 2007). All these facts explain why horn size in mountain ungulates has important and diverse implications for conservation biology and evolution (Coltman et al., 2002;Singer and Zeigenfuss, 2002), although not much work has been done in domestic ungulates. ...
Article
Fluctuating asymmetry (FA) refers to small random deviations from perfect bilateral symmetry. Directional asymmetry (DA) is defined as population-level deviations from bilateral symmetry that are unimodal and significantly different from symmetry. Lastly, antisymmetry (AS) is a pattern of bilateral variation in which differences exist between sides, but the side that is larger varies randomly among individuals. FA reflects the ability of individuals to undergo stable development, so it may provide a potential measure of individual quality. FA is not likely to be adaptive but both DA and AS are developmentally controlled and are therefore likely to have adaptive significance. Twenty-seven adult females belonging to the Catalan goat population (NE Spain) were studied to assess horn perfect symmetries (in total length and base circumference) as indicators of their fitness. Symmetry was tested by means of Wilcoxon signed test and dispersion values. Platykurtic distributions and plotting the cumulative frequency was used to assess DA and AS. For horn length, but not for horn circumference, AS was revealed. Although AS has been considered to be developmentally controlled and possibly adaptive, the specific processes producing this pattern in Catalan goat horn remain a matter of discussion.
... Wildlife management agencies also regulate hunting to enhance hunter opportunity and experience on public lands by manipulating season lengths, opening dates, and hunter density to delay animal movement to private lands (Conner et al. 2001, Vieira et al. 2003. Hunting can directly alter movements and distribution (Proffitt et al. 2010, Cleveland et al. 2012, Neumann and Ericsson 2018, social organization (Singer and Zeigenfuss 2002), and genetics (Kardos et al. 2018) of ungulate populations, and indirectly affect disease spread (Davidson et al. 2012, Apollonio et al. 2017) and population performance (Davidson et al. 2012, Festa-Bianchet et al. 2017. ...
Article
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Sport hunting of ungulates is a predominant recreational pursuit and the primary tool for managing their populations in North America and beyond, given its influence on ungulate distributions, social organization, and population performance. Similarly, land management, such as motorized vehicle access, influences ungulate distributions during and outside hunting seasons. Although research on ungulate responses to hunting and land use is widespread, knowledge gaps persist about space use of hunters and what landscape features discriminate among hunt types and between successful and unsuccessful hunters. We used telemetry location data from hunters (n = 341) to estimate space use from 2008–2013 during 3 types of controlled, 5‐day hunts for antlered mule deer (Odocoileus hemionus) and elk (Cervus canadensis) in northeastern Oregon, USA: archery elk, rifle deer, and rifle elk. To evaluate space use, we developed utilization distributions for each hunter, created core areas (50% contours) for groups of hunters, and derived several metrics of space‐use overlap between successful and unsuccessful hunters. We also modeled predictors of space use using resource utilization functions with beta regression and stepwise model building. Hunter space use was compressed, with even the largest core area (unsuccessful rifle elk hunters) encompassing <16% (1,178 ha) of the area. We found strong similarities in space use of rifle hunters compared to archers, and core areas of successful hunters were markedly smaller than those of unsuccessful hunters (e.g., = 104 ha vs. 681 ha, respectively, for archers). Percentage cover and distance from open roads were the most consistent covariates in the 6 final models (successful vs. unsuccessful for each of 3 hunts) but with different signs. For example, predicted use of archery and rifle elk hunters increased with cover but decreased for rifle deer hunters. Although the same covariates were in the final models for unsuccessful and successful rifle elk hunters, their negligible spatial overlap suggested they sought those features in different locales, a pattern also documented for rifle deer hunters. Our models performed well (Spearman's rank correlation coefficients = 0.99 for 5 of 6 models), reflecting their utility for managing hunters and landscapes. Our results suggest that strategic management of open roads and forest cover can benefit managers seeking to balance hunter opportunity and satisfaction with harvest objectives, especially for species of special concern such as mule deer, and that differences in space use among hunter groups should be accounted for in hunting season designs. © 2021 The Wildlife Society. This article has been contributed to by US Government employees and their work is in the public domain in the USA. We evaluated space use of successful and unsuccessful elk and mule deer hunters, contrasting archers with rifle hunters, and found minimal spatial overlap between groups but similarities in environmental features influencing space use. Integrated management of forest cover in tandem with roads and trails can aid in providing hunter opportunity while maintaining herd numbers and composition at desired levels.
... En effet, bien que les jeunes mâles soient souvent sexuellement mâtures, l'accès à la reproduction est plus tardif et ils pourraient donc ne pas avoir la même capacité que les adultes à inséminer un grand nombre de femelles (Solberg et al. 2002). Certains auteurs suggèrent même que les jeunes mâles ne seraient pas capables de stimuler l'oestrus des femelles (Singer & Zeingenfuss 2002 ;Holand et al. 2006). Ainsi, si le système d'appariement est perturbé, il est possible que la fécondité, la survie de certaines catégories d'individus (une classe d'âge ou un sexe) et la sexe ratio des jeunes soit également perturbée (voir Milner et al. 2007 pour une revue récente). ...
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Among Ungulates, the wild boar (Sus scrofa scrofa) is characterised by a mixture of particular life history traits which associate a high fecundity and an early age at first reproduction with a large body size and a potential long life expectancy. Moreover, unlike most ungulates which are rather strict herbivores, the wild boar is an omnivore. This uncommon life-history strategy is associated with an increase in population size. Indeed, in Europe, wild boar populations are currently still growing and cause some socio-economical problems due to the damage that wild boars generate to the human activities. Hence the understanding of the factors primarily involved in this increase in population size as well as the modelling of population dynamics is now essential to better manage wild boar populations. This work rely on a long term data set (25 years) of a hunted wild boar population in the eastern part of France (Haute-Marne). The analyses of maternal allocation in reproduction highlighted that in utero, the sex ratio decreased as litter size increased. Sex ratio was male-biased for litter size up to 6 and then became female-biased in larger litters. Producing large female-biased litters may be an adaptive adjustment to avoid strong sibling competition during lactation and therefore to maximise the number of recruited offspring. The threshold weight above which females can reproduce is around 28 kg live weight but once females become sexually mature, they will reproduce every year. However, the onset of oestrus may be delayed according to the available resources and vary year-to-year. Natural mortality was disentangled from hunting mortality by using Capture-Recapture multi-states models. Males’ survival did not vary yearly but did vary with age-classes and the probability to be hunted increased with age up to around 70%. Females’ survival did vary yearly and also differed between age-classes with the yearly survival probability of females younger than one-year old being smaller than that of older females. Compared to other large mammals, adult females’ survival was lower and more variable over time possibly because of higher reproductive investment, especially in young adults. Those demographic characteristics reveal that wild boars could not be managed like other ungulate species. So, we developed a new modelling approach and retained a sex-specific body mass dependent model to assist managers. In this way, managers have the possibility to directly test the outcome of the model by comparing observed and expected distributions of wild boars killed by hunters among sex- and body mass-specific classes. They can assess the performance of a given hunting rule and simulate the respective efficiency of management scenarios. KEY WORDS: Wild boar ; Sus scrofa scrofa ; Ungulate ; France ; population dynamics ; management model ; multi-state model ; Capture-Mark-Recapture ;demography ; sex-ratio ; maternal allocation ; hunted population
... No other studies have shown significant phenotypic changes in ungulates that could be attributed to selective hunting. Singer and Zeigenfuss [50] offer an alternative view regarding genetic diversity and removal of old males: … trophy hunting permits more subdominant and smallerhorned rams to obtain copulations, and thus may increase the ratio of effective population size to census population size (Ne:N) and thus increase total genetic diversity. ...
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Regulated hunting is the foundation of the North American Model of Wildlife Conservation. This conservation paradigm arose out of a movement, lead by prominent hunters, to stop over-exploitation of wildlife by market hunters and the desire to have wildlife accessible to all people. Since then, hunters have contributed billions of dollars to wildlife management that benefit countless wildlife species. These funds support wildlife management agencies which manage all wildlife species, not just those that are hunted. This unique and successful conservation paradigm is responsible for supporting a wide variety of conservation activities, including law enforcement, research, information and education, habitat management and acquisition, as well as wildlife population restoration and management. Although wildlife conservation activities embrace far more than the hunted species, hunters continue to be the primary agents of financial support, management assistance and organized advocacy.
... Milner-Gulland et al., 2003b). Alternatively, the removal of only a few experienced adult males may be sufficient to jeopardize population growth or maintenance through the alteration of reproductive phenology (Noyes et al., 1996;Singer & Zeigenfuss, 2002). However, we doubt that it occurred in our study areas; despite the proportion of adult males tending to be lower and to decline in the hunting areas compared with the national park, the same pattern was not observed in population densities. ...
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The persistence of large African herbivores in trophy hunting areas is still unclear because of a lack of data from long-term wildlife monitoring outside national parks. We compared population trends over the last 30 years in Hwange National Park, Zimbabwe, and the neighbouring Matetsi Safari Area where large herbivores were harvested at an average yearly rate of 2%. We investigated whether trophy hunting altered densities and the proportion of adult males in several large herbivore species. Large herbivores generally thrived as well, or even better, in the hunting areas than in the national park. The proportion of adult males did not differ between the two zones, except for species with higher harvest rates and proportionally more males harvested. Densities were not lower in the hunting areas than in the national park, except for elephant and impala. Large herbivores generally declined throughout the 30-year period in both zones, particularly selective grazers. This is probably because of their greater sensitivity to variation in rainfall compared with other herbivores. Rainfall indeed declined during the study period with droughts being particularly frequent during the 1990s. Browsers, mixed feeders and non-selective grazers generally declined less in the hunting areas than in the national park, possibly because of lower densities of natural predators and elephants outside the park. Our study highlighted that large herbivores may persist in trophy hunting areas as well as in national parks. When rigorously managed, trophy hunting areas may be relevant conservation areas for large herbivores, particularly under the current global decline of wildlife abundance across Africa.
... Although trophy hunting rarely influences population size, population structure may be altered by the disproportionate removal of animals relative to age or sex (Milner et al. 2007, Mysterud 2012, Lindsey et al. 2013. Additionally, shifts in the proportion of unique phenotypes (Wilfred 2012, Monteith et al. 2013, Rivrud et al. 2013, Coulson et al. 2018, LaSharr et al. 2019b or behavioral traits (Singer andZeigenfuss 2002, Leclerc et al. 2019) also may occur. Considerable speculation exists about the biological effects of trophy hunting, but much remains unknown (Harris et al. 2002, Festa-Bianchet and Lee 2009, Festa-Bianchet 2016, Festa-Bianchet and Mysterud 2018. ...
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Reported effects of trophy harvest often are controversial. The subject is nuanced and many studies lack details necessary to place their results in context. Consequently, many studies are misunderstood or their conclusions misapplied. We propose that all dialogues about trophy hunting include a definition of how they use the term trophy, details of variables measured and why they were selected, and explanations of temporal and spatial scales employed. Only with these details can potential effects of trophy hunting be understood in context and used for management and policy decisions. © 2021 The Wildlife Society. Effects of trophy harvest often are controversial because many studies lack important details. Dialogues about trophy hunting must include a definition of how they use the term trophy, details of variables measured and why they were selected, and explanations of temporal and spatial scales employed so that potential effects of trophy hunting can be understood in context.
... Since the reproductive effort of old males is highest during the peak-rut period, young males may avoid pursuing females during this time as it would provoke aggression from old males. Similarly, Singer and Zeigenfuss (2002) found that young male Dall sheep (Ovis dalli) increase their reproductive effort when adult males are scarce or absent. Thus, young male reindeer might resort to an alternative mating tactic, whereby they perform their most energetically costly activities earlier in the mating season when competition from old males is less intense. ...
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In polygynous species, male reproductive effort has been measured both directly in the form of somatic costs and indirectly using behavioral data. We used 12 years of data collected from a semi-domesticated reindeer population in northern Finland to inves-tigate age-and time-specific patterns of dominant males' reproductive effort. Overall, we found that activity levels differed both between young and old dominant reindeer males, and among the early, peak, and late rut, the pattern being age-specific. Repro-ductive effort was generally higher for old than young dominant males; however, old males reduced their effort in the late-rut period, while young males maintained the same level of activity. There was a positive relationship between somatic costs and activity level only during the early rut for young dominant males, and only during the peak rut for old dominant males. Thus, old males incur the highest energetic costs from rut-related activities when most of the females in the herd are in oestrus. Conversely, young males appear to time their rut-related energetic cost to coincide with the early rutting period, before most females have reached oestrus. Old males are more efficient in timing their reproductive effort so as to maximize their reproductive success. This can be attributed to young males being less experienced than old males or to using an alternative mating tactic by young males who try to avoid competition with old males during the peak rut.
... Similarly, according to Mi l ne r et al. (2007), the elimination of individuals from the population by hunting not only reduces its density, but above all disturbs its ecological structures. In addition, mating involves enormous energy expenditure (He w is on et al. 1996), which leads to higher mortality among weak bucks in winter (Si nge r and Z e i gen f uss 2002, Myster ud et al. 2003. Features describing the condition of individual animals may be seasonally variable and dependent on the deficiency of nutrients or the physiological state of the body, e.g. ...
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The aim of this study was to assess changes in parameters (body weight, fat stores, antler weight, serum creatinine level) describing the condition of individual roe deer males (Capreolus capreolus) in subsequent months of the hunting season. The idea was if the current timing of the buck hunting season affects the quality of specimens obtained from the population, which may result in distorting its reproduction-related processes. The study included 443 carcasses of bucks harvested in the Lublin region (Central Poland) from 2006 to 2011. The average carcass weight in May and June was significantly higher than in the other months. Perirenal fat weight and the kidney fat index (KFI) decreased with the progression of the hunting season. With regard to the average level of serum creatinine in blood, there was no definite trend in the variation of this parameter during the hunting season. However, a significantly higher average antler weight was observed in May compared to June. The shooting of a large number of bucks in the first weeks of the hunting season may cause the elimination of the best individuals in the habitat, which have established and maintained their territory and are fully prepared for reproduction. This results in a complete disruption of the social structure of the local deer population. A solution to this problem could be uniform distribution of volume harvested during the whole hunting season or postponing the hunting season for bucks until September, when the estrus season has finished, and the strongest males have passed on their valuable genes to the population.
... White-tailed deer (Odocoileus virginianus) altered their habitat use and timing of daily activity to avoid hunters [10]. Hunting led to reduced intraspecific competition, decreased mating opportunities, and increased group size in red deer (Cervus elaphus) and Dall sheep (Ovis dalli), likely due to the removal of dominant individuals [10,11]. Understanding the effects of harvest and anthropogenic activities on behavior, resource selection, and population dynamics is fundamental to conservation. ...
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Pressure from hunting can alter the behavior and habitat selection of game species. During hunting periods, cervids such as elk ( Cervus canadensis ) typically select for areas further from roads and closer to tree cover, while altering the timing of their daily activities to avoid hunters. Our objective was to determine the habitat characteristics most influential in predicting harvest risk of elk. We captured 373 female elk between January 2015 and March 2017 in the Uinta-Wasatch-Cache National Forest and surrounding area of central Utah, USA. We determined habitat selection during the hunting season using a resource selection function (RSF) for 255 adult cow elk. Additionally, we used a generalized linear mixed model to evaluate risk of harvest based on habitat use within home ranges (3 rd order selection) as well as the location of the home range on the landscape to evaluate vulnerability on a broader scale. Female elk selected for areas that reduced hunter access (rugged terrain, within tree cover, on private land). Age, elevation and distance to roads within a home range were most influential in predicting harvest risk (top model accounted for 36.2% of AIC weight). Elevation and distance to trees were most influential in predicting risk when evaluating the location of the home range (top model accounted for 42.1% of AIC weight). Vulnerability to harvest was associated with proximity to roads. Additionally, survival in our landscape decreased with age of femaleelk.
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Trophy hunting is a management goal for many populations of ungulates and has important implications for conservation because of the economic value of trophy males. To determine whether population density affected horn growth of males, a marked population of bighorn sheep (ovis canadensis) in Alberta, Canada, was studied for 27 years. For the first 9 years, population density was kept stable by removing adult females; afterwards, the numbers of ewes and yearlings tripled before beginning to decline. Horns were measured during repeated captures of marked rams. As the number of adult ewes and yearlings increased, ram horns were shorter and thinner because of decreased horn growth before 4 years of age. Some compensatory horn growth may have occurred at 5 years of age. The effects of population density on horn growth ceased when rams left the nursery groups to join all-male groups. Doubling of male numbers had no detectable effect on net annual horn growth of males greater than or equal to 4 years old. Sp
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Reduced forage intake by males is generally believed to coincide with the peak of rutting activities in many ungulates. Activity budgets of bull moose (Alces alces) in Denali National Park and Preserve (DNPP) and Isle Royale National Park (IRNP) were analyzed to assess: (1) if time spent foraging decreased during the rut; (2) the timing of reduced forage intake; (3) whether there was variation in feeding time among bulls of varying size; and (4) the proximate mechanism and adaptive value of reduced forage intake. Time spent feeding by bull moose began to decrease around 1 September: large bulls completely ceased feeding for approximately 2 weeks, with median dates of feeding cessation at 18 and 20 September for IRNP and DNPP, respectively. Small bulls fed at reduced rates, but did not cease feeding. Although large bulls in both study sites spent large amounts of time engaged in social behavior during the period of appetite suppression, much of their active time was also spent standing inattentive, i.e., engaged in no activity (45.5% in IRNP, 29.8% in DNPP), suggesting that a constraint in time budgets did not limit opportunities to feed. Forage intake reduction is more likely mediated through a physiological mechanism. Feeding cessation did not coincide with the peak of the rut: at DNPP the median date of feeding cessation was significantly earlier than the median date of breeding behavior and fighting. The timing of feeding cessation coincided with that of scent-urination at both study sites, raising the possibility that appetite suppression may be a byproduct of physiological processes associated with chemical communication.
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Some wildlife biologists and managers are concerned that ungulate population productivity may decline when hunting causes a bias in the male age structure favoring young males. Young males are assumed to be incapable of successfully courting females, to prolong the mating season, to create confusion during mating because of unstable social hierarchies, or to cause some combination of these. Here, results are presented of a natural experiment involving two bighorn sheep (Ovis canadensis candensis) populations: one unhunted and the other where most of the mature males were removed during the hunting season. One month later, the remaining young males courted and successfully copulated with adult estrous females. Comparing courtship behavior of these young males with that of males more than three times their age in the unhunted population with a “typical” male age structure, showed no significant qualitative or quantitative differences. However, young males in the unhunted population not only failed to copulate with estrous females but also performed mainly immature patterns in male-male interactions, even when they were the largest males in the interaction. Social maturation in mountain sheep is not simply a function of chronological age but is related to a population's social structure and composition.
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Population numbers, age-sex composition, and the male age structure of Dall sheep (Ovis dalli) were studied in Mount McKinley National Park, Alaska, in the summer of 1972. Age of living males was estimated either by counting horn annuli from photographs taken in the field or, if annuli could not be discerned in the photographs, on the basis of horn size. The correlation of age with horn size first was determined for the former group by multiple regression analysis; the resultant equation then was used to estimate age in the latter group. Composition ratios and the sample of males whose ages were estimated were used to establish the age structure of the living male segment of the population. The results demonstrated that the age structure had not been stationary over the past several years. Differences in numbers in each age-class were due to marked variability in initial size and in mortality rates of the cohorts comprising the population. Quantitative analysis of skull data collected by A. Murie from 1937 to 1941, which have been used widely in the construction of life tables, demonstrated that the age structure was not stationary during the period the skulls accumulated. Analyses of changes in population size and of variation in natality rates suggested that the pattern of the life tables was due not only to variation in age-specific survivorship but also to marked variation in initial size of the actual cohorts comprising the samples. Natality was inversely correlated with snowfall and density. First-year survivorship was not correlated with natality rate, indicating that the factors affecting these demographic parameters varied substantially from year to year.
Article
I studied the reproductive cycle of Dall sheep (Ovis dalli dalli) in 3 herds in the Kenai Mountains, Alaska. The rut was predicted to extend from 16 November through 19 December 1970, and from 18 November through 18 December 1971. All adult ewes collected throughout the winter were pregnant. Three of 4 yearling ewes were pregnant and no female lambs had reached puberty. Although some long yearling rams appeared physiologically capable of reproduction, they were unlikely to participate in breeding activities because of behavioral constraints. The mean gestation period was 171 days. Fetal growth curves are presented. Lambing dates were not uniform between years or herds. Peak dates of lambing for the 3 herds over 4 yr ranged from 20 May to 31 May. Lambing success averaged 31.8 lambs per 100 ewes and was not significantly different from the statewide average of 36.6. There were negative correlations between increasing winter snow depth and lambing success and between average maximum winter winds and snow depth. Positive correlation was found between average maximum winter temperatures and snow hardness, which, in turn, was negatively correlated with lambing success.
Article
In three sampling areas (two unhunted, one hunted), we compared activity patterns of Dall sheep rams (Ovis dalli) of different horn size during the rut. In all three areas rams with horns and smaller rams were less frequently seen in ewe bands as the rut progressed. In one area where we documented activity budgets, we observed equivalent budgets for ewes and rams with horns . Older rams spent less time foraging than young rams, except that rams with horns curled spent less time foraging than full-curl rams late in the rut. Display frequencies of rams were similar to those of full-curl rams and considerably higher than those of smaller-horned rams early in the rut. These results suggest that the rut is more energy costly for old rams than for young rams, but that it may be most costly for the next-to-largest horn-curl class rams (e.g. rams in unhunted populations) rather than the dominant rams (full-curl and larger). Rams in the next-to-largest horn-curl class in the hunted herd, however, did not acquire the higher display rates (e.g., rams had equally low display rates in both the hunted and unhunted herds).
Article
Horn segment counts were compared with chronological age of 21 bighorn rams (Ovis canadensis) of known age, and were found to coincide.
Article
Seventy-two tanned, dehaired hides of four species of cervids from western Canada were examined for evidence of injuries. Combat injuries were segregated from injuries incurred from other sources. Forty-six of 55 males 1.5 years of age and older were scarred, as were 14 of 15 females. Of 15 males 1.5 years of age, 7 showed no scars, nor did two 6-month-old male fawns. Only 1of 22 male cervids over 2.5 years of age showed no combat scars. The frequency of wounding in males was 0–225, and in females0–18 per individual. About three-quarters of the scars were on the neck and haunches, about equally divided between these areas. The longest healed scar measured 420 mm; about 20% of the scars exceeded 100 mm in length. Field observations greatly underestimate wounding in cervids. A few males appear to opt out of rutting, but opt in when opportunity allows. The "dove" strategy is rare, but evidence from hides indicates that it does exist, confirming field observation.
Article
Ovis canadensis studied in Colorado preferred open habitats with a high density of acceptable forages and avoided habitats with vegetation obstructing visibility. Ewes and rams were more alert than were juveniles during foraging periods; ewes with young lambs were most alert. Intra-group spacing was positively correlated with habitat visibility. Foraging efficiency was negatively related to distance from escape terrain and positively related to habitat visibility and to group size. Foraging in large groups (>10 sheep) appears to be a behavioral adaptation enabling sheep to utilize less secure habitats.-from Authors
Article
The mating behavior of an insular Armenian wild sheep population (Ovis orientalis gmelini) and a Transcaspian urial (Ovis orientalis arkal) population was quantified during the rutting season in December 1972, and November and December 1973, respectively. Males were grouped into two age classes; Class I (less-than-or-equal-to 4 years) and Class II (greater-than-or-equal-to 5 years). Typically, older rams prevent younger rams from participating in the rut through threatening gestures; subadult rams will not ordinarily challenge adult rams as was the case in the Transcaspian population. In the Armenian population, subadult rams hurriedly approached ewes and chased and mounted ewes. Subadult Armenian rams disrupted the social stability of the population resulting in wasted energy, particularly in ewes, at a critical time of the year. Wildlife managers should monitor wild ungulate populations to determine if such disruptions are occurring and develop preventative management strategies.
Article
We examined Dall sheep (Ovis dalli) populations in Alaska to determine if the harvest of old rams affected either the survival of young rams or lamb and yearling production. We hypothesized that proportions of young rams would be lowest in areas where old rams were most heavily harvested if survival of young rams is depressed when old rams are culled. However, there were no significant (P > 0.05) relationships between the proportions of young and old rams in analyses of helicopter and ground surveys or fixed-wing aerial surveys. Two comparisons of population composition between nearby unhunted and hunted populations showed no relationship between the harvest of old rams and the proportions of young rams in the populations, and no effect of hunting on lamb or yearling production was evident. Likewise, a comparison of population composition in 2 areas soon after closure to hunting and several years later showed no clear relationship in proportions of old rams and young rams. Overall, survival of young rams and production of lambs and yearlings did not appear to be affected by harvest of old rams, but the hypothesis deserves more rigorous testing.
Article
1. Several aspects of the foraging behavior of California bighorn sheep (Ovis canadensis californiana) were studied in homogeneous habitats in the interior of British Columbia, Canada. The manner in which an individual sheep foraged was based upon the size of group within which it was found. 2. In small groups (five or less individuals) sheep foraging efficiency was poor and interruptions of foraging to scan the environment were frequent. 3. Alarm vocalizations and other conspicuous behaviors tend to alert their neighbors to the presence of disturbances. It appears that these signals cannot be based solely as the result of kin selection.
Article
1. The sexual behaviour of a chimpanzee community in the Gombe National Park, Tanzania, was studied intensively for 16 months. Additional information came from 15 years of demographic and behavioural data accumulated by Jane Goodall and members of the Gombe Stream Research Centre. 2. The mating system of the Gombe chimpanzees is flexible and comprises three distinct mating patterns: (a) opportunistic, non-competitive mating, when an oestrous female may be mated by all the community males; (b) possessiveness, when a male forms a special short-term relationship with an oestrous female and may prevent lower-ranking males from copulating with her; and (c) consortships, when a male and a female leave the group and remain alone, actively avoiding other chimpanzees. While males took the initiative in possessive behaviour and consortships, females had to cooperate for a successful relationship to develop. 3. Data from 14 conceptions indicated that the majority of females (9) became pregnant while participating in the restrictive mating patterns, possessiveness and consorting. It could be established definitely that seven of these females were consorting during the cycle in which they conceived. As 73% of the 1137 observed copulations occurred during opportunistic mating, 25% during possessiveness, and only 2% during consortships, there was no correlation between copulation frequency and reproductive success. 4. Adult males showed differential frequencies of participation in the restrictive mating patterns. Male age, dominance rank, and the amount of agonistic behaviour directed to females showed no correlation with participation in the restrictive mating patterns. The following male characteristics did show significant, positive correlations with involvement in the restrictive mating patterns: (a) the amount of time spent in the same group as oestrous females, (b) the proportion of that time spent grooming oestrous females in groups, and (c) the frequency with which males shared food with females. While dominance ranks of the adult males showed no consistent correlation with involvement in the restrictive mating patterns, it was clear that the most dominant male did gain an advantage. He was the only male able to monopolise oestrous females by showing possessive behaviour. 5. Consortships appeared to be the optimal reproductive strategy for males (with the exception of the most dominant) and females, as they gave males the highest probability of reproductive success, and allowed females to exercise choice. However, there appeared to be disadvantages associated with consort formation; the greatest of these was the increased risk of intercommunity encounters. While all individuals have the potential to practice each mating pattern, the strategy actually used at any moment will be determined by variables both within the individual, e.g. age, physical condition, dominance position; and by social factors in the group, e.g. general stability of male dominance relationships, presence of a strong alpha male, existence of special male-female relationships.
Article
Rocky Mountain bighorn rams use three distinct tactics in competition for mates. Two tactics (tending and blocking) feature defense and cooperative mating over a relatively prolonged consort period (up to 3 days). In the coursing tactic, subordinate rams fight dominants for temporary copulatory access (lasting seconds) to defended ewes. By combining population-wide genetic (microsatellite) exclusion of paternity, behavioral data and a model of bighorn reproductive competition, we estimated that coursing rams fathered 44% of 142 lambs assigned paternity in two natural populations. In one population, the probability of successful defense against coursing was lowest among rams that had many female consorts and held highest dominance rank. Even so, per capita annual male reproductive success was positively associated with social rank in both herds when measured in terms of fall conceptions. The proportion of coursing versus defending ram matings in each population (0.36 and 0.39) was similar to the corresponding fraction of lambs (0.43 and 0.47) fathered by coursing rams, suggesting that sperm competition approximated a fair lottery. Male traits important in gaining social status and obtaining cooperative consorts with ewes were different and potentially in conflict with those needed to defend against (and practise) coursing. Although the concussive weapons (horns) of rams are less dangerous than, for example, the piercing weapons of other bovids, injury from falls and horn blows during coursing brawls may cause death, handicap future mating competition or increase the risk of predation. Coursing is a rare example of an unconventional alternative mating tactic that is high-gain and high-risk.
Article
Since the process of natural selection entails a comparison of phenotypes and choosing of the best, optimality theory appears appropriate to identify selection pressures. Optimality theory doesnot test whether an organism is designed optimally — it assumes it. The ingredients of a complete optimization model are outlined and two approaches are exemplified. Both time-energy-budgeting and Pontryagin's maximum principle lead to semi-quantitative predictions about, e.g., an animal's behavior; they merely entail an inequality formalism. A discrepancy between prediction and test would not yet show a behavior to be maladaptive since several other explanations are possible. Animals optimize their behavior over intervals ranging from less than a second to months or years. It is unknown whether, with a long interval, the animal makes use of the opportunity to revise its decision(s). Present optimal foraging models predicting, e.g., diet breadth are too simple in that foragers a) may not always maximize energy intake, as postulated, b) have to allow for nutrient, toxin and remedial content of food items, and/or c) have to allow for interaction of items, annihilating their ranking along a unidimensional scale of profitability.
Article
For red deer stags, fighting both has appreciable costs and yields considerable benefits. Up to 6% of rutting stags are permanently injured each year, while fighting success and reproductive success are closely related, within age groups as well as across them. Fighting behaviour is sensitive to changes in the potential benefits of fighting: stags fight most frequently and most intensely where potential benefits are high and tend to avoid fighting with individuals they are unlikely to beat. The relevance of these findings to theoretical models of fighting behaviour is discussed.
Article
Observations were made on greater kudu (Tragelaphus strepsiceros) in the Kruger National Park in South Africa. Data on movement patterns, courtship, dominance interactions and proportion of time spent in various activities by males during the breeding season are presented. Comparative data on the apportionment of time by red deer (Cervus elaphus) setages were obtained on the Isle of Rhum, Scotland. While spatial components of male reproductive behaviour were similar in the two species, time-investments differed markedly. Kudu bulls showed little change in time spent feeding and moving during the breeding season, did not herd females and tolerated the presence of younger males. In contrast, red deer stags almost ceased feeding and greatly increased their time spent moving and in sexual or dominance-related activities. Thus the spatial and temporal components of male mating strategies can vary independently and require separate evolutionary explanaions. Comparative data for other ungulates are sparse, but suggest that time-investments are influenced by the duration of the breeding season and the breeding sex ratio. However, kudu bulls incur high mortality costs despite their low time-investments in reproductive activities.
Article
Not all members of a sex behave in the same way. Frequency- and statusdependent selection have given rise to many alternative reproductive phenotypes within the sexes. The evolution and proximate control of these alternatives are only beginning to be understood. Although game theory has provided a theoretical framework, the concept of the mixed strategy has not been realized in nature, and alternative strategies are very rare. Recent findings suggest that almost all alternative reproductive phenotypes within the sexes are due to alternative tactics within a conditional strategy, and, as such, while the average fitnesses of the alternative phenotypes are unequal, the strategy is favoured in evolution. Proximate mechanisms that underlie alternative phenotypes may have many similarities with those operating between the sexes.
Article
The single greatest obstacle to the restoration of large, healthy, populations of bighorn sheep (Ovis canadensis) in the western United States is epizootic outbreaks of bronchopneumonia that may kill 20-100% of the animals in populations. Although the species is capable of rapid initial growth rates following restoration into new habitat (lambda = 1.23-1.30 have been observed), these rates of increase are typical only a few years following the release of a population, and then most populations either decline to extirpation or remnant status (<30 animals) or remain at <100 individuals. We studied the fecundity and survivorship of three increasing, and three declining and suspected diseased, populations of bighorn sheep (the latter were subjected to outbreaks of bronchopneumonia) located in or near several large national parks in the western United States from 1991 to 1996. Titers verified both population categories were exposed to the bacteria Pasteurella haemolytica serotypes 3; 4; and 3, 4, 10; Moraxella sp., and parainfluenza-3 and bluetongue (BT) viruses. Pregnancy rates of adult ewes were not different in increasing or decreasing populations (pooled rate = 0.93; p = 0.57), but pregnancy rates of yearlings were lower (0.00 for decreasing vs. 0.33 for increasing populations), initial production of lambs and annual recruitment of lambs was lower (0.14, decreasing vs. 0.66, p < 0.05). Adult survival was lower during: the first year of an epizootic, 0.62, in one population, but recovered to 0.85 by the second and subsequent years. Survival of adult rams was variable in diseased populations; in two populations rams appeared to be disproportionately impacted, but in a third population rams survived better during the epizootic. In all the increasing park (unhunted) populations, adult ram survival (0.94 +/- 0.01) was higher than adult ewe survival (0.89 +/- 0.02) (p = 0.10), in contrast to published information from hunted populations where ram survival was lower. Removal of about 20% of one population for restorations severely impacted one declining population. Removals of 12-20% appeared to be excessive and were not readily compensated for in the Canyonlands National Park desert bighorn population. Disease was a significant limiting factor to restoration of bighorn sheep in the study areas; six of 11 total recovering populations we monitored closely were negatively influenced by apparent disease at some time during our observations.
Article
ZusammenfassungEs werden soziale Verhaltensmuster amerikanischer Wildschafe beschrieben.Die Schafe wurden nach ihrer äußeren Erscheinung in 7 oder 8 Klassen eingeteilt, die stufenförmig vom Lamm zum alten, großgehörnten Widder führen. Es ergab sich:1Schafe von gegenüberliegenden Enden dieser Reihe schließen sich in eigene Gruppen zusammen: eine “Altherrngruppe” und eine “Mutter-Kindgruppe”.2Geschlechtsreife Widder können mit Schafen aller Klassen Beziehungen aufnehmen, Weibchen und Jungtiere dagegen fast ausschließlich mit Schafen von ihren eigenen Körper- und Horngrößen abwärts.3Widder bevorzugen als Sozialpartner ♂♂ gleicher Horngröße oder erwachsene ♀♀4Widder behandeln alle Rangtieferen gleich, ob ♂♂, ♀♀ oder Jungtiere.5Das erwachsene, nicht brünftige ♀ benimmt sich wie ein geschlechtsunreifes Jungtier, das brünftige ♀ wie ein geschlechtsreifes untergeordnetes ♂.6Schafe lassen sich in zwei typische Verhaltensgruppen einteilen: eine der “Männer” und eine der “Jugendlichen”.7Jede Gruppenbildung beruht auf dem Antagonismus dieser beiden Schlüsseltypen, welche ihrerseits auf sozialen, innerartlichen Verhaltensweisen begründet sind. “Männergruppen” bestehen daher nicht nur aus Widdern, sondern schließen auch die brünftigen ♀♀ ein; und die “Mutter-Kindgruppe” setzt sich aus nicht-brünftigen Schafen und nicht-geschlechtsreifen Jungtieren zusammen, welche alle dem Verhaltenstypus der “Jugendlichen” angehören.8Wenn untergeordnete Widder einem Dominanten gegenüberstehen, geben sie sich offenbar für ein brünftiges ♀ aus.9In die Schafsozietät wird das Individuum nicht nach Alter und Geschlecht eingeordnet, sondern nach seiner Größe und Rangordnung.
Article
Rocky Mountain bighorn rams obtained copulations by defending single estrous ewes (tending), fighting tending rams for temporary access to defended ewes (coursing), or moving and holding ewes away from other rams beyond the periphery of a traditional tending area (blocking). Coursing and blocking illustrate a feature of many male alternative mating strategies: the ability of males regularly to create mating opportunities.
Article
The view that high social rank is associated with high levels of both copulatory behavior and the production of offspring is widespread in the study of animal behavior. In order to demonstrate the validity of this hypothesis it is necessary first to resolve ambiguities in the concept of dominance and to assign ranks by means of valid procedures. Second, copulatory behavior must be properly sampled, measured, and related to rank. Finally, it must be demonstrated that rank and increased copulatory behavior actually lead to increased reproduction. Each step in this process entails conceptual and methodological difficulties. There have been many studies of rank and copulatory behavior, fewer of rank and differential reproduction, and very few of rank, copulatory behavior, and differential reproduction. The consistency of results obtained varies with taxon; results of particular consistency appear in studies of carnivores and ungulates. Both the concept of dominance and the validity of the hypothesis relating it to copulatory behavior and to differential reproduction appear viable for at least some species, although the body of data relating rank to both copulation and differential reproduction remains minimal.