No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Age, resource availability, and breeding effort in Brandt's cormorant
... The population sizes, diets, vital rates, and behaviors of seabirdsbird species that depend on the marine environment for food resourcesare often used as indicators of change in the marine environment (Boekelheide and Ainley 1989;Diamond and Devlin 2003;Einoder 2009;Pichegru et al. 2010;Ronconi et al. 2012;Velarde et al. 2013;Elliott et al. 2015). Methods for sampling and estimation of these metrics in seabirds are thus a key part of their application as indicators. ...
... Therefore, seabird vital rates are often measured to help assess biological and physical parameters of the marine environment (Boekelheide and Ainley 1989;Einoder 2009;Ronconi et al. 2012;Velarde et al. 2013;Elliott et al. 2015). Reproductive success, and variation in reproductive success, is one vital rate that is widely measured in seabird biology, in an effort to indicate changes in the marine environment, or understand basic questions about ecology or conservation of seabirds (Diamond and Devlin 2003;Mallory et al. 2010;Ronconi et al. 2012;Velarde et al. 2013;Elliott et al. 2015). ...
... When variation in seabird reproductive success is suggested to indicate changes in the marine environment without identifying the proximate causes of such variation, inference is limited to association, and the proximate causes themselves (such as parental care or diet) could prove more effective as indicators (Mallory et al. 2010 year, 2) variation in reproductive success between years, and 3) compared nest success to individual egg and chick success between years. Cormorants are different from most other seabirds in that they have relatively large clutch sizes and variable adult survival, which is thought to be a result of changing marine conditions and food availability because they rely on the same nearshore marine ecosystem year-round (Boekelheide and Ainley 1989;Ainley 1990a;Ainley 1990b;Wallace and Wallace 1998;Weimerskirch 2002). Variability in seabird reproductive success often relates strongly to variability in foraging success, and foraging success depends on current marine conditions (Cairns 1987;Hipfner et al. 2007). ...
Variation in reproductive success is widely measured in seabird biology in an effort to indicate changes in the marine environment, or understand basic questions about ecology or conservation of seabirds. When variation in seabird reproductive success is suggested to indicate changes in the marine environment without identifying the proximate causes of such variation, inference is limited to association, and the proximate causes themselves could prove more effective as indicators. My study informs this problem by examining and quantifying proximate causes of variation in reproductive success, at the level of nests and individual chicks. I used video of Brandt's Cormorant (Phalacrocorax penicillatus) nests on Castle Rock National Wildlife Refuge (NWR) to monitor parental care behaviors and test their influence on reproductive success in 2015. I also estimated annual variation in survival of both nests and individual eggs and chicks from 2011-2015 on Castle Rock NWR. Lastly, I compared nest survival to individual egg and chick survival to evaluate and improve upon how seabird reproductive success is traditionally measured. iii Parental care behaviors had no statistical influence on survival in 2015, but nest and individual egg and chick survival varied dramatically from 2011-2015 (nest survival range: 0.083-0.942; individual survival range: 0.037-0.719). Derived estimates of nest survival from egg and chick survival demonstrated validity of measuring individual survival. My results demonstrated that inclusion of proximate causal factors that influence reproductive success and contemporary parameter estimation methods help inform seabird biology and current monitoring techniques.
... Most Brandt's cormorants do not return to the colony until at least age 2 when some individuals begin breeding. A small fraction (<5%) return to the colony and are observable at age 1 but do not breed [25]. We classified individuals into three states based on breeding status [26]: pre-breeder (individuals that have never been recorded breeding), breeder (individuals confirmed breeding in a given year), and non-breeder (bred at least once previously, observed at the colony not breeding). ...
... We carried both age structures forward through the next two steps at which point models with the two and four age classes still had nearly equal support (ΔQAICc < 2) so we proceeded with the more parsimonious structure (2 age classes, immature = age 0-1, and adult = age 2+). We also viewed this age structure as the most biologically realistic since it is likely most age related differences in recapture probability are driven by low colony visitation rates for immature individuals (age 0-1) compared to adults (age 2+) rather than differences among adults of different age categories [25]. The effect of age on breeding probability (transition into breeder state) was best modeled as an inverse relationship (1/age, S4 Table). ...
... The high recapture probability for breeding individuals is likely a result of breeding site fidelity and the extended recapture period (~5 months). An individual breeding in the study area is likely to return the following year to breed in the same area [25] and would have many opportunities to be seen and resighted throughout the course of the breeding season. Recapture probabilities from 2000-2002 were exceptionally low ( Fig 2D) and in one year (2001) were estimated to be essentially zero, consistent with a known reduction in resighting effort during that period. ...
With a rapidly changing climate, there is an increasing need to predict how species will respond to changes in the physical environment. One approach is to use historic data to estimate the past influence of environmental variation on important demographic parameters and then use these relationships to project the abundance of a population or species under future climate scenarios. However, as novel climate conditions emerge, novel species responses may also appear. In some systems, environmental conditions beyond the range of those observed during the course of most long-term ecological studies are already evident. Yet little attention has been given to how these novel conditions may be influencing previously established environment–species relationships. Here, we model the relationships between ocean conditions and the demography of a long-lived seabird, Brandt’s cormorant (Phalacrocorax penicillatusI), in central California and show that these relationships have changed in recent years. Beginning in 2007/2008, the response of Brandt’s cormorant, an upper trophic level predator, to ocean conditions shifted, resulting in lower than predicted survival and breeding probability. Survival was generally less variable than breeding probability and was initially best predicted by the basin-scale forcing of the El Niño Southern Oscillation rather than local ocean conditions. The shifting response of Brandt’s cormorant to ocean conditions may be just a proximate indication of altered dynamics in the food web and that important forage fish are not responding to the physical ocean environment as expected. These changing relationships have important implications for our ability to project the effects of future climate change for species and communities.
... Most Brandt's cormorants do not return to the colony until at least age 2 when some individuals begin breeding. A small fraction (<5%) return to the colony and are observable at age 1 but do not breed [25]. We classified individuals into three states based on breeding status [26]: pre-breeder (individuals that have never been recorded breeding), breeder (individuals confirmed breeding in a given year), and non-breeder (bred at least once previously, observed at the colony not breeding). ...
... We carried both age structures forward through the next two steps at which point models with the two and four age classes still had nearly equal support (ΔQAICc < 2) so we proceeded with the more parsimonious structure (2 age classes, immature = age 0-1, and adult = age 2+). We also viewed this age structure as the most biologically realistic since it is likely most age related differences in recapture probability are driven by low colony visitation rates for immature individuals (age 0-1) compared to adults (age 2+) rather than differences among adults of different age categories [25]. The effect of age on breeding probability (transition into breeder state) was best modeled as an inverse relationship (1/age, S4 Table). ...
... The high recapture probability for breeding individuals is likely a result of breeding site fidelity and the extended recapture period (~5 months). An individual breeding in the study area is likely to return the following year to breed in the same area [25] and would have many opportunities to be seen and resighted throughout the course of the breeding season. Recapture probabilities from 2000-2002 were exceptionally low ( Fig 2D) and in one year (2001) were estimated to be essentially zero, consistent with a known reduction in resighting effort during that period. ...
Background/Question/Methods
In the central California Current, annual productivity is primarily determined by the wind-driven upwelling of nutrients. In this bottom-up system, we expect parallel trends in productivity across trophic levels. For this study, we utilized 41 years of data from the Farallon Islands in California, to examine recent contrasting trends in productivity between two seabird species at different trophic levels: the piscivorous Brandt’s Cormorant (Phalacrocorax penicillatus), and the planktovorous Cassin’s Auklet (Ptychoramphus aleuticus). We often assume that a species’ relationship to the environment is stable through time. Here, we test the hypothesis that contrasting productivity trends for these two species are linked to changes in how each species responds to the environment. We used a sliding correlation analysis with a 10-year window to examine how ocean conditions (measured locally and basin-wide) influence productivity of each seabird species and how these relationships change over time.
Results/Conclusions
We found that both species productivity initially responded strongly to El Niño variability. In the last 15 years, the response of Cassin's Auklet productivity to El Niño weakened. At the same time, the correlation between Cassin’s Auklet productivity and the North Pacific Gyre Oscillation (NPGO) increased. This occurred at about the same time that productivity of the two species began to diverge. The amplitude of variability of NPGO has been increasing in recent decades. High variability and novel conditions may have facilitated a shift from a strictly El Niño dominated system to one where NPGO is an increasingly important driver of productivity. Our analysis has shown that the relationships between seabird productivity and physical forcing can change over time and the changes differ by trophic level. Understanding what influences these non-stationary relationships will be critical for population modeling and predicting the consequences of future climate change for marine systems.
... Although this might be reasonable for most of the observed population levels, it is almost certainly unrealistic at the high abundances possible with a theoretical model. For this population of Brandt's cormorant, there has been no direct evidence of habitat or nest site limitation Ainley 1989, Ainley andBoekelheide 1990;Nur and Sydeman 1999). However, density-dependent competition for prey is expected to increase throughout the breeding season as birds switch from incubating eggs to feeding multiple chicks several times daily consequently increasing the demand for nearby prey. ...
... In one songbird example, estimates of apparent survival for adult yellow warblers were 6-22% lower than true survival when dispersal was not accounted for (Cilimburg et al. 2002). Immature and pre-breeding Brandt's cormorants rarely visit the breeding colony and are nearly unobservable with fewer than 5% of age 1 Brandt's cormorants observed returning to their natal colony (Boekelheide and Ainley 1989). As a consequence, our estimates for first and second year survival are almost certainly the most biased and uncertain. ...
As global climate changes, there is increasing need to understand how changes in the frequencies of environmental variability affect populations. Age-structured populations have recently been shown to filter specific frequencies of environmental variability, favoring generational frequencies, and very low frequencies, a phenomenon known as cohort resonance. However, there has been little exploration of how changes in the spectra of environmental signals will affect the stability and persistence of age-structured populations. To examine this issue, we analyzed a likely example to show how changes in the frequency of an influential climate phenomenon, the El Niño-Southern Oscillation (ENSO), could affect a marine bird population. We used a density-dependent, age-structured population model to calculate the transfer function (i.e., the frequency-dependent sensitivity) of Brandt’s cormorant (Phalacrocorax penicillatus), a representative marine bird species known to be influenced by ENSO. We then assessed how the population would be affected by ENSO forcing that was doubled and halved in frequency. The transfer function indicated this population is most sensitive to variance at low frequencies, but does not exhibit the sensitivity to generational frequencies (cohort resonance) observed in shorter-lived species. Doubling the frequency of ENSO unexpectedly resulted in higher mean adult population abundance, lower variance, and lower probability of extinction, compared to forcing with the historical or reduced ENSO frequency. Our results illustrate how long-lived species with environmentally driven variability in recruitment, including many species of marine birds and fish, may respond in counterintuitive ways to anticipated changes in environmental variability.
... Therefore, their population sizes generally vary very little from one year to the next independent of the annual variations of the food con-dition (Furness & Camphuysen 1997). However, in some seabird species adult birds can skip breeding and potential new recruits can choose not to establish breeding territories and nests in years of food shortage (Boekelheide & Ainley 1989;Bradeley et al. 2000;Pyle et al. 2001), thus the population abundance can decrease in the years of food shortage. Although in those species population abundance can respond sensitively to annual variations in the food condition, only a few studies have shown a close relationship between breeding population abundance and food condition (Crawford & Dyer 1995;Phillips et al. 1996;Parsons et al 2008). ...
... Seabirds are considered to decide whether to breed or not before the breeding season commences (Boekelheide & Ainley 1989;Bradeley et al. 2000;Pyle et al. 2001), then decide to lay eggs or not during the early stage of breeding (Giudici et al. 2010;Goutte et al. 2010), and to continue or abandon their offspring after starting to breed (Yorio & Boersma 1994;Crawford & Dyer 1995). Their decisions are thought, therefore, to be dependent on the food conditions during the different periods and in different areas. ...
Breeding population abundance such as colony size of seabirds is not generally considered to be particularly sensitive to the annual dynamics of the food conditions because of the long life-span and high adult survival rate. However, in seabird species in which adults decide to breed or not depending on the food conditions, population abundance can respond sensitively to the annual variation in the food conditions. Here, we examine the effects of the regional annual stock abundance of Japanese Sand Lance Ammodytes personatus, and their local temporal availability during the egg-laying period on the size of a Black-tailed Gull Larus crassirostris and Slaty-backed Gull L. schistisagus, breeding colony over 12 years on Rishiri Island, northern Japan. The total number of nests of both gull species increased significantly with the regional annual stock abundance, but not with the local temporal availability of the sand lance. The number of Black-tailed Gull nests without eggs was significantly higher in the year with lower local temporal availability indicating that more Black-tailed Gull parents gave up egg-laying after nest building. Colony size in these species can be a useful indicator reflecting local food conditions.
... However. established birds may refrain from breeding in some years (Coulson 1984, Boekelheide & Ainley 1989, Murphy et nl. 1991). ...
... 1991). Similarly, potential new recruits may choose not to establish territories if conditions are unfavourable (Boekelheide & Ainley 1989, Coulson 1991). If food availability influences either of these factors, fluctuations in the size of the breeding population might have some value as an indicator of environmental conditions. ...
Analysis of kleptoparasitic interactions of Arctic skuas Stercorarius parasiticus foraging within sight of Foula, Shetland, indicated that the skuas were able to switch hosts if particular species (notably Arctic terns Sterna paradisaea) were breeding unsuccessfully in a given year. Adult Arctic skuas spent considerably longer foraging off-territory in 1987, when sandeel (mainly Ammodytes marinus) recruitment in Shetland waters was low, than they did in 1979 or from 1992-1994. Both Arctic skua chick growth and fledging success were depressed during the years of low sandeel availability. But they were able to breed with moderate success up until at least 1986, in sharp contrast to Arctic terns which failed from 1983 to 1990. Breeding Arctic skua adults appeared to be in poorer body condition in 1988, the second year of particularly low sandeel recruitment, and there was also strong evidence that many established pairs deferred breeding in that year and in 1990.
... Numerous studies have documented the coupling of annual variations in seabird breeding success with climatic and oceanographic variations that affect food availability (e.g. Anderson, Gress & Mais 1982;Duffy 1983;Boekelheide & Ainley 1989). Such linkages provide an opportunity to use historical data on environmental correlates of reproduction as proxies to evaluate short-term data sets on reproduction in an historical perspective (Murphy, Springer & Roseneau 1986). ...
... El-Ninio -Southern Oscillation (ENSO) events, complete failures generally appear to be relatively rare (e.g. Schreiber & Schreiber 1989;Boekelheide & Ainley, 1989). ...
(1) All aspects of reproductive performance of kittiwakes (Rissa tridactyla L.) fluctuated markedly in 1975-89 at a colony of about 10 000 nesting pairs in the north-eastern Bering Sea, Alaska. (2) In breeding seasons following cold springs, breeding was delayed, fewer nests were built, fewer nests contained eggs, and clutch size, hatching success and the number of chicks fledging per nest were reduced. Complete reproductive failures followed the three coldest springs in the 15-year period. (3) Reproductive success (chicks fledged per nest) was highest following moderately warm springs; however, growth rates of chicks and fledging success were extremely low following the warmest spring on record. (4) Spring air temperatures were highly correlated with break-up of sea ice and these factors probably influenced seasonal warming trends in the sea water and the consequent availability of prey such as sandeels (Ammodytes hexapterus Pallas) near the colony. (5) During this 15-year period, interannual variability in spring air temperature was pronounced in comparison to that during the previous 68-year period; however, simulations using May temperature as a predictor of reproductive success suggested that high annual variability in reproduction has occurred throughout this century. (6) Numbers of adult-plumaged birds on the cliffs in mid-season were markedly lower and more variable in years when few nests were built, suggesting that relatively few experienced adults breed and consistently are present at the colony in years when overall reproductive performance is poor.
... A significant drop in the available food supply was implicated as the reason behind at least one of the crashes (Aebischer 1986, Aebischer & Wanless 1992. Boekelheide & Ainley (1989) also observed that the number of Brandt's Cormorants (Pbalacrocorax penicillatus) that abandoned or skipped breeding varied greatly from year to year depending on food availability. ...
... Immigration of nesting shags to the peninsula from unknown, outlying sites is unlikely based on the high degree of natal philopatry and nest site fidelity observed in the Phalacrocoracidae. The majority of Brandt's Cormorants at Southeast Farallon Island, California nested within 300 m of their natal colony (Boekelheide & Ainley 1989). In European Shags, Potts (1969) found that only 8% of first-time breeders nested outside their natal colony, and that less than 1% changed colonies thereafter. ...
In 1960, a census of the Spotted Shag (Stictocarbo punctatus punctatus) population on Banks Peninsula found 9,787 breeding pairs (Turbott & Bell 1995). Here we report the results of a comparative census conducted on Banks Peninsula during the 1996 breeding season. Thirty-six years after the original census, the number of breeding pairs was found to have more than doubled to 22,123 pairs. We speculate that the population was formerly limited by food availability and that a reduction in fishing effort around Banks Peninsula, especially in the late 1980s, may have contributed to the observed growth in the shag breeding population.
... At a population level, the proportion of individuals that breed within a year is an important determinant of population growth (Cam et al. 1998). The broad relevance of the propensity or decision to breed has resulted in considerable theoretical (e.g., Goodman 1974, Charlesworth 1980, Stearns 1992) and empirical (e.g., Boekelheide and Ainley 1989, Aebischer and Wanless 1992, Chastel et al. 1995, Reed et al. 2004, Le Bohec et al. 2007) work exploring optimal decisions from a life-history perspective and proximate drivers of variation in this demographic rate. ...
... The probability of breeding commonly varies with age in iteroparous species. Delayed maturation in long-and medium-lived species is common (Clutton-Brock 1988, Newton 1989, and age-at-first-breeding is positively related to density (Weimerskirch andJouventin 1987, Krüger 2005) and negatively related to wetland numbers (a proxy for drought ;Afton 1984) and prey availability (Boekelheide andAinley 1989, Brommer et al. 1998). After onset, breeding probability generally increases with age, often reaching an asymptotic value that, in some species, later declines with the onset of senescence (Afton 1984, Sedinger et al. 2001, Crespin et al. 2006. ...
The decision to breed influences an individual's current and future reproduction, and the proportion of individuals that breed is an important determinant of population dynamics. Age, experience, individual quality, and environmental conditions have all been demonstrated to influence breeding propensity. To elucidate which of these factors exerts the greatest influence on breeding propensity in a temperate waterfowl, we studied female Lesser Scaup (Aythya affinis) breeding in southwestern Montana. Females were captured during the breeding seasons of 2007-2009, and breeding status was determined on the basis of (1) presence of an egg in the oviduct or (2) blood plasma vitellogenin (VTG) levels. Presence on the study site in the previous year, a proxy for adult female success, was determined with stable isotope signatures of a primary feather collected at capture. Overall, 57% of females had evidence of breeding at the time of capture; this increased to 86% for females captured on or after peak nest initiation. Capture date and size-adjusted body condition positively influenced breeding propensity, with a declining body-condition threshold through the breeding season. We did not detect an influence of age on breeding propensity. Drought conditions negatively affected breeding propensity, reducing the proportion of breeding females to 0.85 (SE = 0.05) from 0.94 (SE = 0.03) during normal-water years. A female that was present in the previous breeding season was 5% more likely to breed than a female that was not present then. The positive correlation between age and experience makes it difficult to differentiate the roles of age, experience, and individual quality in reproductive success in vertebrates. Our results indicate that individual quality, as expressed by previous success and current body condition, may be among the most important determinants of breeding propensity in female Lesser Scaup, providing further support for the individual heterogeneity hypothesis.
... Theoretical models (e.g., Stearns 1976) assume that when food is limited there is an increase in reproductive costs, which will be higher for younger breeders under these environmental conditions. Some of the few studies addressing the association between food supply (mostly estimated through proxies such as climate indexes or fisheries data), age, and breeding parameters have found that differences in breeding performance between age classes were highest when food was in short supply (Boekelheide and Ainley 1989, Sydeman et al. 1991, Laaksonen et al. 2002, Bunce et al. 2005); see Fig. 1a. A second, unexpected pattern derived from theoretical expectations (see Fig. 1b) indicates that when food availability is high, breeding parameters are equally high for all age classes (Ratcliffe et al. 1998, Nevoux et al. 2007, Lee 2011. ...
... When food per capita was in short supply, the resulting quadratic age pattern was less marked (Fig. 5), even though most studies have found that differences in breeding performance between age classes decrease with improving feeding opportunities (see Appendix: Table A1). For instance, Ezard et al. (2006) report that young Common Terns (Sterna hirundo) performed well only in highquality years, as is the case in Brandt's Cormorants (Phalacrocorax penicillatus) (Boekelheide and Ainley 1989). By contrast, our results show that the quadratic age pattern in Audouin's Gull for all parameters is more apparent under good conditions (except for laying dates; see Fig. 5), when middle-aged individuals greatly improve their breeding performance, thereby increasing differences in reproductive performance vis-a`-vis older birds. ...
We used a long-term data set (26 years) from Audouin's Gull (Larus audouinii), a long-lived seabird, to address the relationship between the age-dependent pattern of reproductive performance and environmental conditions during breeding. Although theoretical models predict that the youngest and oldest breeders (due to inexperience and senescence, respectively) will perform less well than intermediate age classes, few empirical data exist regarding how this expected pattern varies with food availability. To assess the influence of age and food availability (corrected by population size of the main consumers to take into account density dependence) on a number of breeding parameters (laying dates, egg volume, clutch size, and hatching success), we modeled mean and variances of these parameters by incorporating heterogeneity into generalized linear models. All parameters varied with age and to different degrees, depending on food availability. As expected, performance improved with increased food supply, and the observed age pattern was quadratic, with poorer breeding performances occurring in extreme ages. For most parameters (except for laying dates, for which age and food did not interact), the pattern changed with food somewhat unexpectedly; the differences in performance between age classes were higher (i.e., the quadratic pattern was more noticeable) when food was more readily available than when food availability was lower. We suggest that, under poor environmental conditions, only high-quality individuals of the younger and older birds bred and that the differences in breeding performance between age classes were smaller. Although variances for egg volume were constant, variances for laying dates were highest for the youngest breeders and tended to decrease with age, either due to the selection of higher-quality individuals or to a greater frequency of birds skipping breeding with age, especially when food was in low supply. Our results show that mean and variances of breeding parameters changed with age, but that this pattern was different for each parameter and also varied according to food availability. It is likely that, other than food, certain additional factors (e.g., sex, cohort effects, density dependence) also influence changes in breeding performance with age, and this may preclude the finding of a common pattern among traits and among studies on different taxa.
... Site fidelity and mate fidelity do not always coincide. Even for species that are moderately faithful to their breeding site, environmental instability (greater flamingo, Phoenicopterus ruber roseus: C ezilly & Johnson, 1995), low adult survival rate (ptarmigans, Lagopus lagopus and Lagopus leucurus: Hannon & Martin, 2002) or asynchronous arrival to a breeding site (Brandt's cormorant, Phalacrocorax penicillatus: Boekelheide & Ainley, 1989; penguins, Aptenodytes patagonicus and Aptenodytes forsteri: Bried et al., 1999) can incur a high cost of waiting for a former mate before starting to breed and lead to a high rate of mate switching (i.e. low mate fidelity). ...
... Empirically, two patterns are observed. In one, poor environments enhance age effects because the performance of young and/or old animals suffers more than that of middle-aged animals, due to inexperience or senescence, respectively (e.g., for age at first breeding, clutch size, hatching success, and fledgling success; Boekelheide & Ainley, 1989. In the other, good environmental conditions (not poor ones) enhance age effects because middle-aged animals are better able to take advantage of abundant resources than other age classes are (e.g., in young versus experienced seabirds for foraging efficiency; Daunt et al., 2007, and meal mass;Limmer & Becker, 2009). ...
Foraging outcomes dictate the nutritional resources available to an organism and may vary with intrinsic factors, like age. Thus, understanding how age affects foraging performance, alone or in interaction with extrinsic factors (like environmental quality), improves our understanding of aging processes in the wild. We examined how foraging traits, measured across five breeding seasons, change with age, environmental variation, and their interaction in Nazca boobies (Sula granti), a pelagic seabird in Galápagos. We evaluated the hypotheses that (1) foraging performance is better in middle-aged birds than in young ones, and that (2) foraging performance is better in middle-aged birds than in old ones. Furthermore, favorable environmental conditions will either (3) attenuate age differences in foraging performance (by relieving constraints on young, inexperienced and old, senescent age classes), or (4) accentuate age differences (if middle-aged birds can exploit abundant resources better than other age classes can). Incubating birds tagged with GPS loggers (N = 815) provided data on foraging performance (e.g., total distance traveled, mass gained) to evaluate interactions between age and environmental variation (e.g., sea surface temperature). Poor environmental conditions associated with the cool phase of the El Niño-Southern Oscillation increased foraging effort, including foraging distance and duration, for example. Across age classes, foraging boobies responded similarly to environmental variation except for female mass gain rate: age-related declines in mass gain rate were reduced under favorable environmental conditions. Birds of different ages also searched in somewhat distinct areas in the poor conditions of 2016, but not in other years. In several foraging traits, including foraging duration and distance, female boobies showed predicted early-life improvement and late-life decline, following the established pattern for reproductive traits in this species. Thus, deficits in resource acquisition (this study) may contribute to the poor survival and reproductive outcomes previously observed in old Nazca boobies, particularly in females.
... Newton 1989, Saether 1983, Desrochers & Magrath 1993, Espie et al . 2000, several others have found no correlation between age, clutch size or fledging success (Davis 1976, Nol & Smith 1987, Boekelheide & Ainley 1989. Moreover, although several studies have attempted to determine the impact of landscape heterogeneity and age on animal reproductive performance and demography (e.g. ...
... That tendency is also observed in other seabirds (e.g. Brandt's Cormorant [Phalocrocorax pencillatus]; Boekelheide and Ainley 1989), and as in other seabirds (e.g. Wandering Albatross [Diomedia exulans]; Weimerskirch 1992); the decision on whether or not to recruit is likely to be mediated through the physiological condition of individual females. ...
There is growing awareness that costs associated with egg production play a significant role in shaping avian life histories. The life-history strategy of the Thick-billed Murre (Uria lomvia), a colonial, cliff-breeding seabird of Arctic waters, is characterized by a high annual adult survival rate, deferred breeding, and laying of a single-egg clutch. The single-egg clutch is a widespread phenomenon among seabirds and is generally thought to reflect demands of chick provisioning, rather than egg production. We compared composition of eggs laid by Thick-billed Murres most likely to be physiologically constrained in their capacity to produce eggs (young females with no prior experience, and females forming replacement eggs) to that of first eggs laid by early laying females (typically older, more experienced members of the population). Young, inexperienced females laid 4–18 days past the populationwide median laying date, and their eggs averaged 13% lighter in mass than those laid by early layers. Compared to early laid eggs, shell mass on young females’ eggs was similar to that predicted from egg mass, but their eggs had a lower yolk-to-albumen ratio. There was little difference between the two groups in relative protein content of albumen, relative protein or lipid content of yolk, or amino acid makeup of protein in yolk or albumen. Replacement eggs averaged 6% lighter in mass than first eggs laid by the same females earlier that season. As with young females’ eggs, replacement eggs had shells similar in mass to that predicted from egg mass, but lower yolk-to-albumen ratios, when compared to early laid eggs. Both protein and lipid concentrations in yolk were similar in first and replacement eggs, but replacements were deficient in albumen protein. Amino acid makeup of protein in yolk and albumen was similar in the two groups. Those results suggest that any limitations on egg production acting on young, inexperienced females are manifested in delayed laying and reductions in overall egg mass and proportional yolk content, but not in variation in biochemical composition of their eggs. Limitations on females forming replacement eggs are manifested not only in reduced egg mass and yolk content (as with young females), but also in changes in the biochemical composition of eggs; in particular, evidence suggests that relaying females may face a deficit of endogenous protein. The existence of such limitations suggests that demands of egg production can be significant even in a species that lays a single-egg clutch.
... By breeding later and living longer, these metamorphs could achieve equal reproductive success compared to paedomorphs that bred and died earlier. Long-lived metamorphs may offset costs of breeding by increasing years between breeding events, like in many iteroparous organisms (Boekelheide and Ainley 1989;Roff 1992;Stearns 1992;Church et al. 2007). Indeed, across multiple taxa, fewer reproductive events often correlated with a longer life span (Roff 1992;Stearns 1992). ...
Polyphenisms-alternative morphs produced through plasticity-can reveal the evolutionary and ecological processes that initiate and maintain diversity within populations. We examined lifetime fitness consequences of two morphs in a polyphenic population of Arizona tiger salamanders using a 27-year data set with 1,317 adults and 6,862 captures across eight generations. Larval salamanders develop into either an aquatic paedomorph that retains larval traits and stays in its natal pond or a terrestrial metamorph that undergoes metamorphosis. To evaluate the adaptive significance of this polyphenism, we compared lifetime reproductive success of each morph and assessed how life-history strategies and spatiotemporal variation explained fitness. We found sex-specific differences in lifetime fitness between morphs. For males, paedomorphs had more reproductive opportunities than metamorphs when we accounted for the potential mating advantage of larger males. For females, in contrast, metamorphs had higher estimated egg production than paedomorphs. Life-history strategies differed between morphs largely because the morphs maximized different ends of the trade-off between age at first reproduction and longevity. Spatiotemporal variation affected larval more than adult life-history traits, with little to no effect on lifetime fitness. Thus, environmental variation likely explains differences in morph production across time and space but contributes little to lifetime fitness differences between morphs and sexes. Our long-term study and measures of lifetime fitness provide unique insight into the complex selective regimes potentially acting on each morph and sex. Our findings motivate future work to examine how sex-specific selection may contribute to the maintenance of polyphenism.
... (a) High density can increase dispersal of individuals within and between populations. This leads to reduced spatial cohesion of kin (Busch, Waser, & DeWoody, 2009;Clobert et al., 2009;Matthysen, 2005) and a lack of positive spatial genetic structure (Boekelheide & Ainley, 1989;Lowe & Allendorf, 2010). In these cases, the influx of immigrants and survival of recruits leads to more varied genotypes present in a population and less representation of philopatric, older individuals (Peacock & Ray, 2001). ...
Some studies have found that dispersal rates and distances increase with density, indicating that density‐dependent dispersal likely affects spatial genetic structure. In an 11‐year mark‐recapture study on a passerine, the dark‐eyed junco, we tested whether density affected dispersal distance and/or fine‐scale spatial genetic structure. Contrary to expectations, we found no effect of pre‐dispersal density on dispersal distance or the proportion of locally‐produced juveniles returning to the population from which they hatched. However, even though density did not affect dispersal distance or natal return rates, we found that density still did affect spatial genetic structure. We found significant positive spatial genetic structure at low densities of (post‐dispersal) adults but not at high densities. In years with high post‐dispersal (adult) densities that also had high pre‐dispersal (juvenile) densities in the previous year, we found negative spatial genetic structure, indicating high levels of dispersal. We found that density also affected fitness of recruits, and fitness of immigrants, potentially linking these population parameters with the spatial genetic structure detected. Immigrants and recruits rarely nested in low post‐dispersal density years. In contrast, in years with high post‐dispersal density, recruits were common and immigrants had equal success to local birds, so novel genotypes diluted the gene pool and effectively eliminated positive spatial genetic structure. In relation to fine‐scale spatial genetic structure, fitness of immigrants and new recruits is poorly understood compared to dispersal movements, but we conclude that it can have implications for the spatial distribution of genotypes in populations.
This article is protected by copyright. All rights reserved.
... Hill 1984), food availability (e.g. Boekelhdeide and Ainley 1989), female age (e.g. Desrochers and Magrath 1993), and other factors. ...
... Among vertebrates, these strategies include semelparity, where individuals allocate a large amount of resources into one lifetime reproductive event (e.g., salmonids ; Quinn 2011), or iteroparity, where an individual spreads the risk of reproductive failure over multiple breeding events. Iteroparous species that utilize highly variable breeding habitats may adopt different strategies that include: (a) an individual not being able to reproduce in consecutive breeding events due to energetic requirements (e.g., Richardson et al. 1999; Bailey et al. 2004; Converse et al. 2009), (b) an individual choosing to skip a breeding event because of unfavorable conditions (e.g., Boekelheide and Ainley 1989; Aebischer and Wanless 1992), or (c) an individual breeding at every opportunity because of the lack of an ability to determine whether conditions are favorable (den Boer 1968; Gillespie 1974; Slatkin 1974). Church et al. (2007describe these strategies as constrained, facultative breeding, and bet-hedging, respectively. ...
... One of the challenges to effective ecosystem-based management of pelagic ecosystems is the difficulty involved in assessing the abundance of highly mobile, pelagic forage fish. Seabirds have often been mentioned as potentially good indicators of the marine environment: they are relatively easy to study, and their breeding success is often linked to changes in ocean conditions and prey availability (Boehelheide and Ainley 1989;Thayer and Sydeman, 2007). Furthermore, the diet of seabirds has been shown to be strongly correlated with the availability of their prey (Ainley et al., 1993;Miller and Sydeman, 2004). ...
Effective ecosystem-based management requires a comprehensive understanding of the functional links in the system. In many marine systems, forage species constitute a critical link between primary production and upper trophic level marine predators. As top predators, seabirds can be indicators of the forage species they consume and the ocean processes that influence these populations. We analyzed the diet and breeding success for the years 1994, 2003, 2005, and 2007–2012 of the Brandt's cormorant (Phalacrocorax penicillatus), a piscivorous diving seabird, breeding in central California, to evaluate the extent to which cormorant diet composition relates to prey availability, and how diet composition relates to breeding success and ocean conditions. Cormorant diet was primarily composed of young-of-the-year (YOY) northern anchovy (Engraulis mordax), YOY rockfish (Sebastes spp.), and several species of small flatfish (order Pleuronectiformes). YOY rockfish consumption was positively related to their abundance as measured in a late spring pelagic midwater trawl survey. Northern anchovy appeared to be the most important prey as its consumption was positively related to cormorant breeding success. More northern anchovy were consumed in years where warm-water conditions prevailed in the fall season before cormorant breeding. Thus, warm ocean conditions in the fall appear to be an important contributing factor in producing a strong year-class of northern anchovy in central California and consequently a strong-year class of Brandt's cormorant on the Farallon Islands.
... Hill 1984), food availability (e.g. Boekelhdeide and Ainley 1989), female age (e.g. Desrochers and Magrath 1993), and other factors. ...
... Hill 1984), food availability (e.g. Boekelhdeide and Ainley 1989), female age (e.g. Desrochers and Magrath 1993), and other factors. ...
The study of the reproductive biology of House Martins Delichon urbica was carried out in the cities of Guelma and Hammam Debagh, Northeast Algeria during two years 2013 and 2014. Birds of this species produce two broods per year and per breeding pair. At both study sites, the egg-laying period lasted for almost four months. Egg weight and volume differed between broods and years. The mean clutch size was 3.87 ± 1.29, 4.19 ± 1.02 in Guelma and 3.93 ± 1.13, 3.64 ± 1.30 in Hammam in 2013 and 2014, respectively, with a seasonal decline. Hatching success reached 69 and 74.25% in Guelma, and 74.20 and 63.39% in Hammam in 2013 and 2014, respectively. Fledging success was 64.57 and 72.62% in Guelma, whereas, in Hammam it was 72.22 and 58.16% in 2013 and 2014, respectively. Hatching failure was the main cause of mortality. The breeding parameters and morphometrics of the House Martin’s eggs in Algeria determined during our study differed from those reported in previous studies carried out in different parts of Europe.
... Some studies have shown that there is a relationship between resource availability and deferred breeding (e.g. Monaghan et al. 1992;Wernham and Bryant 1998), adult survival (Pons and Migot 1995;Harris et al. 1997;Oro and Furness 2002) or local recruitment rates (Boekelheide and Ainley 1989;. Moreover, unless emigration and mortality are disentangled, decreased food availability may have indirect consequences translating into lower local survival. ...
... Among vertebrates, these strategies include semelparity, where individuals allocate a large amount of resources into one lifetime reproductive event (e.g., salmonids; Quinn 2011), or iteroparity, where an individual spreads the risk of reproductive failure over multiple breeding events. Iteroparous species that utilize highly variable breeding habitats may adopt different strategies that include: (a) an individual not being able to reproduce in consecutive breeding events due to energetic requirements (e.g., Richardson et al. 1999;Bailey et al. 2004;Converse et al. 2009), (b) an individual choosing to skip a breeding event because of unfavorable conditions (e.g., Boekelheide and Ainley 1989;Aebischer and Wanless 1992), or (c) an individual breeding at every opportunity because of the lack of an ability to determine whether conditions are favorable (den Boer 1968;Gillespie 1974;Slatkin 1974). Church et al. (2007) describe these strategies as constrained, facultative breeding, and bet-hedging, respectively. ...
We investigated the influences of natal-pool and metamorph characteristics on juvenile survival, age-specific breeding probabilities, and dispersal of wood frogs (Lithobates sylvatica) and used this information to infer how life history strategies of short-lived species may offset risks associated with breeding in highly variable habitats. We used multistate mark-recapture data from eight wood frog populations in Maryland, USA, to investigate the influences of natal-pond and metamorph characteristics on post-metamorphic demographics. We found that post-metamorphic juvenile survival was highly variable and negatively influenced by abiotic conditions experienced during development but showed little relationship to larval density or size at metamorphosis. Estimates of recruitment and dispersal probabilities indicated that males mature earlier than females, and a small percentage of each sex disperse to non-natal pools. Survival probabilities for adults during the non-breeding season were less variable than juvenile rates, lower for females, and negatively related to mean monthly precipitation. Survival of adults during the breeding season was generally very high. We provide the first robust estimates of post-metamorphic vital rates of wood frogs that allow for variation in capture probabilities. We found little evidence for an effect of metamorph traits on juvenile survival, suggesting that wood frogs may be able to overcome initial disadvantages to have similar post-metamorphic performance. Our study suggests that variation in the age of maturity for wood frogs may mitigate risks associated with breeding in a highly variable habitat to maximize lifetime fitness without increasing lifespan, and this strategy is minimally affected by carry-over effects from the larval stage.
... The ability to modify reproduction as a function of environmental conditions better allows species to exploit variable, unpredictable environments [1,2]. Life-history theory suggests individuals should adopt a bet hedging strategy to maximize fitness in variable environments in which they reduce annual reproduction in poor years to increase survival and lifetime reproductive success [3,4]. ...
In highly variable environments, conditions can be so stressful in some years that entire populations forgo reproduction in favor of higher likelihood of surviving to breed in future years. In two out of five years, Clark's nutcrackers (Nucifraga Columbiana) in the Greater Yellowstone Ecosystem exhibited population-wide failure to breed. Clark's nutcrackers at the study site experienced substantial interannual differences in food availability and weather conditions, and the two nonbreeding years corresponded with low whitebark pine (Pinus albicaulis) cone crops the previous autumn (≤ an average of 8 ± 2 cones per tree versus ≥ an average of 20 ± 2 cones per tree during breeding years) and high snowpack in early spring (≥ 61.2 ± 5.5 cm versus ≤ 51.9 ± 4.4 cm during breeding years). The average adult body condition index during the breeding season was significantly lower in 2011 (-1.5 ± 1.1), a nonbreeding year, as compared to 2012 (6.2 ± 2.0), a breeding year. The environmental cues available to the birds prior to breeding, specifically availability of cached whitebark pine seeds, may have allowed them to predict that breeding conditions would be poor, leading to the decision to skip breeding. Alternatively, the Clark's nutcrackers may have had such low body energy stores that they chose not to or were unable to breed. Breeding plasticity would allow Clark's nutcrackers to exploit an unpredictable environment. However, if large-scale mortality of whitebark pines is leading to an increase in the number of nonbreeding years, there could be serious population-level and ecosystem-wide consequences.
... Studies of cliff-nesting seabirds that share many of the characteristics of the Pelagic Cormorant, including longevity and coloniality, indicate that reuse of nest sites may promote site defense, ensure distance from conspecific nesting pairs, facilitate mate acquisition or retention, and aid in the rapid replacement of a lost mate (Ollason and Dunnett 1988, Boekelheide and ainley 1989, Pyle et al. 2001, huyvaert and anderson 2004. nest-site reuse may be especially important in cliff-nesting species, in which mate acquisition does not involve choice among a dense group of the species at the colony early in the reproductive season (Vergara et al. 2006), although Pelagic Cormorants can form dense groups at roosts near colonies. ...
We photographed nests of Pelagic Cormorants (Phalacrocorax pelagicus) on cliff ledges at two colonies in Mendocino and Sonoma counties, Cali- fornia, from 1986 to 1996. in 135 comparisons of the positions of nests in different years, we found that 92% of the nests shifted by <25 cm (approximate diameter of a Pelagic Cormorant nest), and in 24% of comparisons the shift was <5 cm. Some nests were placed within a few centimeters of previous sites for as long as nine years. the rate of reuse of nest sites was high on both small ledges and on large shelves where the nest could have readily been shifted. at sites where substantial rock substrate sloughed off the cliff face in the previous year, nests were placed precisely at former sites. this high rate of nest reuse is striking because many apparently suitable sites on these cliffs remain unused.
... On the other hand, annual rates of skipping are relatively low in this population and the breeding propensity of guillemots appears to be less sensitive to environmental fluctuations than that of European shags on the Isle of May, where up to 60% of adults may skip breeding in extremely poor years when crashes in population size also occur (Aebischer and Wanless, 1992). Cormorant species in general are prone to such periodic population crashes and rates of non-breeding are also typically highly variable (Duffy, 1983;Boekelheide and Ainley, 1989;Nur and Sydeman, 1999). Thus, population impacts of climate change mediated via changes in breeding propensity will depend on the life history strategy and ecological constraints of the species in question; some species likely have greater scope for regulating breeding effort than others. ...
Climate change may have demographic consequences for marine top predators if it leads to altered rates of skipped breeding. Here we examine variation in skipping propensity at both the population and individual levels in common guillemots Uria aalge in relation to climate and oceanographic variables and explore the extent to which skipping may be adaptive or an unavoidable consequence of ecological or social constraints. We assumed a detection probability for birds present in the colony of 1.00 and skipping events were defined to include both resightings of non-breeders and failures to resight individuals known to be alive (not present at the colony but resighted in future years). Skipping frequency was higher in years where sea surface temperatures (SST) were higher in winter (both in the current and previous year), when guillemots from our study colony disperse widely across the southern North Sea. Individuals differed consistently in their average skipping propensity and their responses to SST. Males and females were equally likely to skip on average and the frequency of skipping increased in the oldest age classes. Birds that skipped in year t had lower breeding success in year t + 1 if they laid an egg, compared to birds that did not skip in year t. Lifetime reproductive output was negatively related to individual skipping frequency. These results imply that skipping is driven by individual-specific constraints, although we cannot rule out the possibility that birds benefit from skipping when environmental (or internal) signals indicate that breeding in poor years could be detrimental to their residual reproductive value. While future climate change might lead to guillemots skipping more often due to carry-over effects from wintering to breeding periods, the net demographic impacts may be subtle as the absolute frequency of skipping may remain low and individuals will not be equally affected.
... O alimento é importante na fase de produção de ovos por influenciar seu tamanho (comprimento, largura e volume) e número no ninho (Lack 1947(Lack , 1948. Tais características têm relação com a qualidade nutricional dos pais antes da postura, sendo que em boas condições de recursos alimentares, muitas espécies tendem a colocar ovos em maior número e volume (Anderson et al. 1980, Hogstedt 1981, Boekelheide & Ainley 1989, Penniman et al. 1990, Sydeman et al. 1991. Isto ocorre devido ao efeito modulatório da disponibilidade de alimento ser capaz de afetar os estádios de maturação dos ovários e determinar a data exata da postura de acordo com as condições de alimento no ambiente (Hau 2001, Jamienson 2007. ...
... However, we also found individual variation in Red-faced Cormorant nesting phenology within years, with replacement clutches initiated at the same time that alpha chicks were beginning to hatch. Older, more experienced breeders may begin laying earlier in the breeding season than younger birds (Hamer et al. 2001), allowing more time to re-nest if first clutches are lost, as observed in Brandt's Cormorants (Phalacrocorax penicillatus; Boekelheide and Ainley 1989). The nesting asynchrony of Red-faced Cormorants could also extend the nestling provisioning period, resulting in less localized prey depletion and increased chick survival (Stempniewicz et al. 2000). ...
Red-faced Cormorants (Phalacrocorax urile) are North Pacific endemics recognized as a vulnerable species, but little is known about their breeding ecology. We studied Red-faced Cormorants on St. Paul Island, Alaska, from 1975 to 2009, with more detailed data collected in 2004 and 2005. Mean clutch sizes in 2004 (3.2 ± 0.8 [SD] eggs) and 2005 (3.1 ± 0.8 eggs) were similar to the long-term average (2.9 ± 0.3 eggs from 1976 to 2009). The mean laying interval in 2004 and 2005 was 2.15 ± 0.80 d (N= 407), and the mean egg period (number of days between laying of an egg and hatching) was 31.1 ± 1.4 d (N= 158). Approximately 64 ± 17% of eggs hatched during the period from 1975 to 2009. The mean number of chicks per nest in 2004 and 2005 was 2.8 ± 0.8 (N= 232), and the mean number of fledglings per initiated nest in all years was 1.22 ± 0.52. Chicks fledged 46 to 66 d posthatching. In 2004 and 2005, the primary causes of egg loss were predation by Arctic foxes (Vulpes lagopus) and destruction of eggs and abandonment of nests due to storms. Starvation was the primary cause of nestling mortality in both years. Because chicks are dependent on parents to provide food for over 45 d, consistent near-shore foraging opportunities must be available. From 1975 to 2009, Red-faced Cormorants experienced only 1 yr of complete reproductive failure (1984). The consistent reproductive success of Red-faced Cormorants suggests that conditions may be relatively stable for this species on St. Paul Island, or that the variability in their breeding ecology (e.g., phenology, clutch sizes, and incubation strategies) provides the flexibility needed to successfully fledge some chicks nearly every year. © 2013 The Authors. Journal of Field Ornithology
... Similarly, midwinter temperature may provide an inadequate characterization of relevant weather conditions. Food supply and age may have interactive effects (Boeckelheide & Ainley 1989, Sydeman et al. 1991, Ratcliffe et al. 1998, Arroyo et al. 2007 ). For example, if the costs of reproduction increase with decreasing food conditions, and age-related breeding patterns are related to reproductive constraints, we should expect that the breeding performance and the probability of whether to breed or not under different conditions change with age: young females should produce less and they should more frequently be non-breeders during low food conditions. ...
The goal of this study was to evaluate the relative role of some central intrinsic and extrinsic factors affecting reproduction in the tawny owl in southern Finland, near the northern limit of the species' range. The data included 153 successful nestings of pairs of birds in which both mates were identified, sexed, aged, and measured. Brood size was constrained by clutch size that, in turn, could be explained by the positive influ-ence of female age. Female condition was positively influenced by both male condi-tion and female age, while male condition was positively related to the age of male. These intrinsic factors outweighed the effects of extrinsic factors examined. However, these probably prominent extrinsic factors, such as general food supply and winter weather conditions, seemed to be inadequately quantified for use in the present study. Therefore, future studies should proceed by evaluating variables that characterize more accurately those environmental conditions where the studied population lives.
... In response, fewer storm-petrels may have attended the colony and a lower proportion of birds may have attempted to reproduce in 1992. This type of multifaceted response to poor food availability has been observed for other Farallon seabirds (e.g., Brandt' s Cormorant, Phalucrocorux penicillutus; Boekelheide and Ainley 1989). Although we have no means of assessing colony attendance, incubation patch characteristics probably explain some of the differences in breeding population size between 1971-1972 and 1992, but these differences are insufficient to account for the overall magnitude of population decline. ...
We conducted a capture-recapture study on the population size and trends of the Ashy Storm-petrel (Oceanodroma homochroa) on Southeast Farallon Island (SEFI), California, based upon data collected in 1971, 1972, and 1992. From March through August, birds were lured to fixed-site sampling locations using taped vocalization playback. Using program JOLLY, we estimated population size and evaluated statistical models using good- ness-of-fit and Likelihood Ratio tests. On the southwestern slope of Lighthouse Hill, amidst prime breeding habitat, numbers of breeding birds decreased from 1,271 2 140 (2 ? SE) in 1972 to 710 ? 117 in 1992, a decline of 44% (approximate 95% CI = 22-66% decline; A = -2.8% per annum); for a variety of reasons, we consider this to be the most reliable indicator of population change. In 197 1, on a portion of SEFI relatively disjunct from the sampling area in 1972, 2,131 2 322 breeding birds were estimated. To produce an overall early 1970s estimate with which to compare to 1992, we summed population estimates from 1971 and 1972. An overall value of 6,461 birds, of which 3,402 (53%) were breeders, was obtained for the early period. In 1992, the overall population in roughly the same area was estimated at 4,284 2 409 birds, of which 1,990 2 408 (46%) were presumed breeders. These results, encompassing peripheral as well as more centrally located storm-petrel habitat, indicate an overall population decline of 34% and a comparable decline in breeding birds of 42% over the past two decades. However, oceanographic conditions varied between 1971- 1972 and 1992, and reduced food availability in 1992 may have influenced colony atten- dance and breeding effort. Nonetheless, the apparent population decline over the past 20 years suggests that the species warrants management and/or additional protective status.
... In other studies of breeding experience where age was controlled for, some reported positive associations with clutch size and/or fledging success (Ainley et al., 1983;Forslund and Larsson, 1992;, while others failed to find any effects (Boekelheide and Ainley, 1989;Davis, 1976;Newton et al., 1981;Nol and Smith, 1987). However, these associations may be due to differences between individuals such that superior birds started to breed at an early age, thereby acquiring more breeding experience at a given age as compared to inferior individuals which may start to breed at an older age . ...
Reproductive success of the cooperative breeding Seychelles warbler (Acrocephalus sechellensis) increases with age. This age effect is not due to differential survival or increased reproductive effort, but to accumulated helping and breeding experience. In their first year of breeding, reproductive performance of inexperienced warblers with neither helping nor breeding experience was significandy lower than that of warblers of the same age with either previous helping or breeding experience. Reproductive performance was die same for primiparae witii helping experience and for birds with breeding experience. Female primiparae with helping experience or breeding experience built better nests and spent more time incubating than inexperienced females, which led to increased hatching success. Male primiparae with helping experience or males with breeding experience guarded the clutch better than inexperienced males, which led to reduced egg predation. Even-aged warblers with different previous experiences were transferred to unoccupied islands, where birds started breeding immediately in high-quality territories. The experiment showed that birds with helping experience produced their first fledgling as fast as experienced breeders, and significandy faster dian inexperienced birds. Breeding performance did not improve further widi experience after the first successful breeding attempt. Only birds with previous breeding experience who paired with inexperienced birds, were likely to change mate. The odier pair combinations remained stable. Thus, primiparous birds with helping experience have greater lifetime reproductive success dian inexperienced primiparae of the same age. This experiment shows that helping behavior has not only been selected for in die context of promoting an individual's indirect fitness, but also in die context of gaining helping experience which translates into improved reproductive success when a helper becomes a breeder. Key words: breeding expe- rience, cooperative breeding, experimental removal, helping experience, reproductive success, Seychelles warbler. (Behav Ecol 7:326-333 (1996))
... There was no difference in fledging success between young and older pairs. Our results accord with several other studies that found younger, inexperienced birds to have lower hatching success than older birds, although those that hatched their egg showed little agerelated difference in the proportion that fledged a chick (Nelson 1964, Coulson and Horobin 1976, Thomas 1983, Boekelheide and Ainley 1989, Weimerskirch 1990). The mass of chicks at 14 d suggested that the rate of provisioning by young pairs was lower than that of older pairs, although the evidence was not conclusive. ...
A seasonal decline in reproductive success is common to many birds breeding in seasonal environments. We examined the reproductive success of Thick-billed Murres breeding at Coats Island, Northwest Territories, Canada to assess the extent to which a seasonal decline in success could be accounted for by correlations between the age of the birds and their date of laying. In 1990 and 1991 reproductive success declined with date of laying: this decline was due mainly to a decline in the proportion of eggs that hatched. No corresponding decline was found in the proportion of hatchlings that reached fledging age. Pairs containing at least one young (4- or 5-yr-old) bird laid later and hatched a lower proportion of eggs than those containing at least one older (>7-yr-old) bird. The two groups did not differ in the proportion of hatchlings reared. When looked at separately, the proportions of young and older birds that succeeded in hatching their egg were not affected by date of laying. When the two age groups were combined, the trends with date were similar to those found for a large sample, mostly birds of unknown age. To correct for differences in timing of laying, a sample of early breeders was induced to lay replacement eggs 14 d later. These experimental pairs were as successful as early control breeders. A greater proportion of the experimentally delayed pairs hatched chicks than birds laying for the first time at a similar date. The experimental pairs were also more successful than young birds that bred earlier. The growth of experimental and control chicks did not differ. However, the 14-d-old chicks of young pairs were lighter than those of experienced breeders, suggesting poorer provisioning by the young breeders. We concluded that there was no evidence for a deterioration in feeding conditions with date and that the relationship between age and/or experience and date of laying was the most important factor in causing the decline in reproductive success with date. Our conclusions may apply to other studies of reproductive success in marine birds.
Description
The first definitive exploration of the effects of this catastrophic oil spill since its occurrence in 1989. In addition to a comprehensive overview of the issues involved, 25 peer-reviewed papers cover the following key topics: • Chemistry and Fate of the Spill • Shoreline Impacts of the Spill • Effects on Fish and Fisheries • Effects on Wildlife • Archaeological Site Impact.
Genetic conflicts among siblings in species with sexual reproduction and parental care, such as birds, manifest as sibling rivalry when nestmates compete for parental resources. Sibling competition is implemented through a diverse array of behavioural mechanisms, ranging from overt aggression and fratricide through non-virulent forms of scramble competition (e.g. begging signals) which may include a high level of tolerance among broodmates or even mutualism. Previous studies suggested that white stork (Ciconia ciconia) nestlings showed little or no aggression or physical interference as a result of parents feeding nestlings simultaneously, by regurgitating food on the nest floor. This pattern, which is shared by other stork species, is however exceptional among other bird families with close ecological and phylogenetic affinities, such as herons, ibises or pelicans. In these groups, nestmates usually compete despotically, often by overt aggression. The aims of this study were: 1) to elucidate the precise behavioural mechanisms regulating nestmate competition and communication within white stork broods, and 2) to unravel the ultimate evolutionary causes underlying variation in levels and mechanisms of nestmate competition among the highly diverse clade of subaltricial birds. First, we obtained behavioural samples from video recordings of natural feeding events involving 108 nestlings from 46 broods less than four weeks old, as well as data from three experimental setups. Second, we performed a phylogenetic comparative study based on a dataset including 192 species belonging to 16 families of altricial birds to determine ecological, behavioural and life-history predictors of the level of interference competition among nestmates. Results showed that white stork broods are characterized by a high level of broodmate tolerance, where interference competition is weak if not completely absent. Moreover, white stork nestlings display an elaborate repertoire of signals containing information about chick nutritional state which seem to be involved in cooperative begging and sibling negotiation, which suggests a highly prosocial evolutionary scenario. The comparative study revealed that the observed diversity
in levels of interference competition among subaltricial birds is closely linked to a species’ life history: more virulent sibling rivalry is associated with a slow life history pace (low fecundity and mortality rates). It is suggested that this association is mediated by both short- and, specially, long-term effects of early nestling behaviour upon viability and fecundity later in life.
We photographed nests of Pelagic Cormorants (Phalacrocorax pelagicus) on cliff ledges at two colonies in Mendocino and Sonoma counties, California, from 1986 to 1996. In 135 comparisons of the positions of nests in different years, we found that 92% of the nests shifted by <25 cm (approximate diameter of a Pelagic Cormorant nest), and in 24% of comparisons the shift was <5 cm. Some nests were placed within a few centimeters of previous sites for as long as nine years. The rate of reuse of nest sites was high on both small ledges and on large shelves where the nest could have readily been shifted. At sites where substantial rock substrate sloughed off the cliff face in the previous year, nests were placed precisely at former sites. This high rate of nest reuse is striking because many apparently suitable sites on these cliffs remain unused.
We studied the breeding biology of the Rock Shag (Phalacrocorax magellanicus) at Punta Loma colony, Chubut, Argentina, during 2001 and 2002 breeding seasons. The egg laying period was long (3-4 months) and asynchronous, while fledging success was low (50%). During the first breeding season, the number of fledglings per nest was not related to laying date, while during the second breeding season there was a reduction in the fledging success of the pairs that laid their eggs late in the season. A high percentage of couples renested after loosing the first clutch (16-22%). In both seasons, the number of chicks fledged in replacement clutches was similar to that in first clutches. The extended and asynchronous egg-laying period, combined with a high rate of renesting (with a fledging success similar to that of single-laying couples), and the low relationship observed between breeding success and laying date, supports the idea of a highly stable and predictable food source for the Rock Shag.
This study was conducted at Tehsil Balakot in District Mansehra, during the breeding season February to June 2014. Details about nests and eggs characteristics are provided. All nests were attached to vertical walls and roofs of buildings and situated at mean height 2.8±0.43 m above ground with nest diameter 14.78±3.13cm, nest depth3.97±0.90 cm, nest cup diameter10.91±2.46 cm and nest cup depth3.27±0.80 cm. Nests attached to cemented walls were (46.3%), plastic surfaces (20.4%), wooden materials (16.7%), soil walls (11.1%) and to mirrors (5.6%). The average clutch size was 3.7 ranged 2-5. Mean egg length was 18.50±1.6 mm, breadth 13.6±1.2 mm, egg volume 1.80±0.5 cm 3 ,egg shape index 1.36±0.03 andegg weight was recorded 1.81±0.1 g. Egg and nest success was 76%and 85%.Hatchling and fledgling produced per nest was 2.84 and 2.44. Main causes for reproductive failures were unhatched and broken eggs, predation and observer's disruption.
This study was conducted at Tehsil Balakot in District Mansehra, during the breeding season February to June
2014. Details about nests and eggs characteristics are provided. All nests were attached to vertical walls and roofs of buildings and situated at mean height 2.8±0.43 m above ground with nest diameter 14.78±3.13cm, nest
depth3.97±0.90 cm, nest cup diameter10.91±2.46 cm and nest cup depth3.27±0.80 cm. Nests attached to cemented walls were (46.3%), plastic surfaces (20.4%), wooden materials (16.7%), soil walls (11.1%) and to
mirrors (5.6%). The average clutch size was 3.7 ranged 2 - 5. Mean egg length was 18.50±1.6 mm, breadth
13.6±1.2 mm, egg volume 1.80±0.5 cm3,egg shape index 1.36±0.03 andegg weight was recorded 1.81±0.1 g. Egg and nest success was 76%and 85%.Hatchling and fledgling produced per nest was 2.84 and 2.44. Main causes for reproductive failures were unhatched and broken eggs, predation and observer’s disruption.
Seabirds, like many taxa of birds in the 19905, face numerous conservation challenges. The primary challenge is to maintain or restore populations in the face of destruction of habitat, introduction of non-native predators, human disturbance (including hunting and collecting),.oil spills, and the like. The low reproductive rates and deferred maturity of seabirds exacerbate the problems (Buckley and Downer, 1992; Croxall and Rothery, 1991), which makes recovery from catastrophic events difficult or even impossible. Seen in this light, nearly all seabird populations can be categorized as “vulnerable,” if not “threatened” or “endangered”; hardly any can be categorized as “not vulnerable” (cf. Mace and Lande, 1991). Over the past decade a multitude of disturbances has affected seabirds, including several major oil spills, of which the Exxon Valdez oil spill is surely the most prominent (Rice et al., 1996; Piatt et al.,1990). Events such as these oil spills have focused the attention of the public, government agencies, and the scientific community on the doubled-headed question: What are the long-term effects of such disturbance, and can seabirds recover from the assault? Interest in answering questions like these is heightened by concern about major oceanographic perturbations, including El Nino events, and activities of commercial fisheries, which could very well undermine the prey base for many seabirds.
Using aerial photography, we examined Brandt's Cormorant Phalacrocorax penicillatus breeding population trends during the 1979-2006 period in the Gulf of the Farallones (GF), California, at the center of the species' breeding range and where its largest single breeding assemblage has occurred (South Farallon Islands [SFI]). In 1979, about 22 000 Brandt's Cormorants bred in the GF, mostly at SFI and mainland colonies north of San Francisco Bay. By 1985, breeding populations were greatly reduced at all active GF colonies following impacts from the strong 1982-1983 El Niño event. During the 1985-1995 period, no trend was detected for SFI, whereas mainland colonies combined increased by 19% per annum. Alcatraz Island inside San Francisco Bay and Año Nuevo Island at the southern end of the GF were colonized, and the new colonies grew rapidly. In 1998, the GF breeding population was again reduced during a strong El Niño. Subsequent growth during the 1998-2006 period was dramatic for all colonies (range 13-29% per annum; 18% combined), associated with strong La Niña conditions during 1999-2000 and high reproductive success during 1999-2006 (except 2003). By 2006, the GF total breeding population was the largest ever recorded (34 876 birds), and the SFI colony had reached a size (~23 500 breeding birds) similar to the previous peak estimate in 1974. Population increase at mainland colonies since the late 1980s likely reflected: 1) immigration of SFI birds; as a result of 2) reduced availability of juvenile rockfishes Sebastes spp. offshore and increased use of Northern Anchovies Engraulis mordax nearshore as prey; and 3) protection of potential breeding habitat.
The quality of a bird’s breeding site is a primary determinant of its success or failure to reproduce there. We expect birds to devote considerable effort to acquiring accurate information about potential locations before finally selecting a breeding site (e.g., Wiens, 1976; Lack, 1971; Howard, 1920). The great mobility of birds strengthens this expectation, which is also reinforced by the accumulating evidence of avian cognitive abilities (e.g., Cook et al., 1997; Cook, 1993). In this chapter we review theoretical considerations and empirical evidence that birds gather advance information about possible breeding sites within a general area before settling to breed within that area. This gathering process, which we term prospecting, has received little systematic attention despite its potential interest and its obvious importance for individual fitness, population dynamics, and distribution.
Brandt's Cormorant (Phalacrocorax penicillatus) diet was investigated using regurgitated pellets (n = 285) collected on 19 sampling days at three locations during the 2006-07 and 2007-08 nonbreeding seasons in the Monterey Bay region. The efficacy of using nested sieves and the all-structure technique to facilitate prey detection in the pellets was evaluated, but this method did not increase prey enumeration and greatly decreased efficiency. Although 29 prey species were consumed, northern anchovy (Engraulis mordax) dominated and speckled sanddab (Citharichthys stigmaeus) also was important in the diet. Few rockfishes (Sebastes spp.) and market squid (Doryteuthis opalescens) were consumed compared with great prevalence in previous studies during the 1970s. El Niño and La Niña during the study provided a unique opportunity to examine predator response to variation in prey availability. Patterns of prey number and diversity were not consistent among locations. Greatest number and diversity of prey occurred at locations within Monterey Bay during La Niña, results not evident at the outer coast location. Short-term specialization occurred but mean prey diversity indicated a generalist feeding mode. This study demonstrated the importance of periodic sampling at multiple locations within a region to detect spatiotemporal variability in the diet of opportunistic generalists.
A recently established breeding colony Branta leucopsis was studied on Gotland, Sweden. Reproductive success increased up to an age of 4-5 yr. Thus, clutch size, number of hatched young and number of fledged young increased, and hatching date was advanced with increasing age. This was due to the fact that individuals increased in reproductive success as they grew older. A possibly higher probability of survival among individuals that perform well in reproduction could not explain the higher reproductive success in older age-classes as compared to young age-classes of geese, because there were no associations between survival and reproductive success, and very few individuals did actually disappear between any two breeding seasons. Path analysis suggested age effects only at earlier stages of reproduction, ie timing of breeding and clutch size. These characters, in turn, were associated with number of fledged young. These findings were further supported by measurements of hatching success and rearing success, which did not seem to increase with age. Increased breeding experience was associated with early hatching date and larger clutch size in males, and with larger clutch size in females. -from Authors
For millenia humans have followed birds at sea to locate fish and mammals. Seabirds are highly visible wide-ranging upper trophic level consumers that can indicate marine productivity and biotic interaction. Compared with fish, marine mammals, and other animals that live primarily or exclusively underwater, seabirds are easy to survey, census and study. This chapter reviews the types, utilities and limitations of avian indicators of the condition of fish stocks and recommends research needed to improve understanding of avian trophic relationships.
This is the action plan for the conservation of the European shag (Phalacrocorax aristotelis) at the Atlantic Islands of Galicia National Park (NW Spain). This area holds one of the largest breeding population for the species worldwide.
Understanding evolutionary consequences of intermittent breeding (nonbreeding in individuals that previously bred) requires investigation of the relationships between adult breeding state and two demographic parameters: survival probability and subsequent breeding probability. One major difficulty raised by comparing the demographic features of breeders and nonbreeders as estimated from capture–recapture data is that breeding state is often suspected to influence recapture or resighting probability. We used multistate capture–recapture models to test the hypothesis of equal recapture probabilities for breeding and nonbreeding Kittiwakes and found no evidence of an effect of breeding state on this parameter. The same method was used to test whether reproductive state affects survival probability. Nonbreeding individuals have lower survival rates than breeders. Moreover, nonbreeders have a higher probability of being nonbreeders the following year than do breeders. State-specific survival rates and transition probabilities vary from year to year, but temporal variations of survival and transition probabilities of breeders and nonbreeders are in parallel (on a logit scale). These inferences led us to conclude that nonbreeders tend to be lower quality individuals. The effect of sex was also investigated: males and females do not differ with respect to survival probabilities when reproductive state is taken into account. Similarly, there is no effect of sex on transition probabilities between reproductive states.
ResearchGate has not been able to resolve any references for this publication.