Variation in Survival and Harvest Rates in Florida Mottled Duck

The Florida mottled duck (Anas fulvigula fulvigula) inhabits a relatively small range of approximately 90,000 km² within peninsular Florida, USA, and is threatened by habitat loss and genetic introgression with feral mallards (Anas platyrhynchos). Moreover, the Florida mottled duck population status has not been assessed for more than a decade. We used band-recovery and recapture data from 2000–2013 to examine geographic and demographic factors that influence the survival of Florida mottled ducks and to determine whether survival and harvest probabilities have changed over time. Mean survival probabilities were higher for birds banded in the southern portion of their Florida range than for those banded in the northern portion and higher for adult males than for adult females in both areas. Harvest probabilities increased in the northern extent of its range in Florida for adults and juveniles and remained relatively constant in the southern portion of its range during the study period. Mean harvest probabilities for adult males in both areas were higher than for adult females. Mean harvest probability for juvenile females was higher than that for juvenile males in the north but was similar between the sexes in the south. Our results suggest that mortality rates are generally greater in the northern portion of the Florida mottled duck range because of regional differences in habitat distribution and permanence and in how mottled ducks and humans use wetlands in these areas. We suggest increasing conservation efforts in the north portion of the Florida mottled duck range and improving inferences from leg banding by incorporating live recapture data. © 2020 The Wildlife Society.     

Lesser Scaup Nest Success and Duckling Survival on the Yukon Flats,Alaska

Abstract: Over the last 20 years scaup numbers have declined, and these declines have been greatest in the northern boreal forests of Canada and Alaska where most lesser scaup (Aythya affinis) nest. We studied nest success and duckling survival of lesser scaup over 3 field seasons, 2001–2003, on the Yukon Flats National Wildlife Refuge in northeastern Alaska, USA. Daily survival rate (DSR) of nests on our study area across all 3 years was 0.943 (n = 177 nests, 95% CI: 0.930–0.954), corresponding to a nest success of only 12.3%, considerably lower than published estimates of an average nest success as high as 57% for lesser scaup in the northern boreal forest. With Mayfield logistic regression, we investigated effects on nest survival of year, clutch initiation date, and nesting habitat type (large wetlands >10 ha, small wetlands <10 ha, and wooded creeks). Neither year nor clutch initiation date influenced nest survival; however, the odds of nest success on large wetlands was 49% lower than on wooded creeks (odds ratio = 0.512, 95% CI = 0.286, 0.918). Based on the model that used only habitat type for estimation, DSR on large wetlands was 0.931 (corresponding nest success = 7.6%), DSR on small wetlands was 0.941 (nest success = 11.1%), and DSR on wooded creeks was 0.963 (nest success = 26.2%). To estimate duckling survival, we monitored 10 broods (n = 75 ducklings) over 3 field seasons by radiotagging hens at nest hatch. Most duckling mortality (94%) occurred in the first 10 days after hatch. Average duckling survival during 1–10 days was 0.321 (95% CI: 0.122–0.772), during 11–20 days was 0.996 (95% CI: 0.891–1.040), and during 21–30 days was 0.923 (95% CI: 0.769–1.041). Three of 10 hens moved all or part of their broods overland between nesting and brood-rearing wetlands for distances of 0.3–1.6 km. Our estimates of lesser scaup nest success and duckling survival on the Yukon Flats were among the lowest ever reported for ducks nesting at northern latitudes, even though the study site was in pristine boreal forest. Estimating and comparing scaup demographic rates from different geographic areas can contribute to improved conservation. Given the scarcity of information on scaup nesting in the boreal forest, basic nesting parameters are important to those trying to model scaup population dynamics.     

Lesser Scaup Breeding Probability and Female Survival on the Yukon Flats,Alaska

ABSTRACT Information on the ecology of waterfowl breeding in the boreal forest is lacking, despite the boreal region's importance to continental waterfowl populations and to duck species that are currently declining, such as lesser scaup (Aythya affinis). We estimated breeding probability and breeding season survival of female lesser scaup on the Yukon Flats National Wildlife Refuge, Alaska, USA, in 2005 and 2006. We captured and marked 93 lesser scaup with radiotransmitters during prelaying and nesting periods. Although all marked lesser scaup females were paired throughout prelaying and incubation periods, we estimated breeding probability over both years as 0.12 (SE = 0.05, n = 67) using telemetry. Proportion of lesser scaup females undergoing rapid follicle growth at capture in 2006 was 0.46 (SE = 0.11, n = 37), based on concentration of yolk precursors in blood plasma. By combining methods based on telemetry, yolk precursors, and postovulatory follicles, we estimated maximum breeding probability as 0.68 (SE = 0.08, n = 37) in 2006. Notably, breeding probability was positively related to female body mass. Survival of female lesser scaup during the nesting and brood-rearing periods was 0.92 (SE = 0.05) in 2005 and 0.86 (SE = 0.08) in 2006. Our results suggest that breeding probability is lower than expected for lesser scaup. In addition, the implicit assumption of continental duck-monitoring programs that all paired females attempt to breed should be reevaluated. Recruitment estimates based on annual breeding-pair surveys may overestimate productivity of scaup pairs in the boreal forest.     

Prefledging Growth and Recruitment of Female Lesser Scaup

Annual variation in juvenile recruitment is an important component of duck population dynamics, yet little is known about the factors affecting the probability of surviving and breeding in the first year of life. Two hypothesized mechanisms to explain annual variability are indirect carry-over effects (COEs) from conditions experienced during the prefledging period and direct effects from climatic conditions during the postfledging period. We used Cormack-Jolly-Seber models to estimate apparent survival and detection rates of 643 juvenile female lesser scaup (Aythya affinis) marked just prior to fledging at Red Rock Lakes National Wildlife Refuge in southwestern Montana, USA, 2010–2018. We evaluated COEs from hatch date, a hatch date × spring phenology interaction, and conspecific duckling density in addition to a direct climatic effect of winter conditions (indexed by the El Niño Southern Oscillation [ENSO]) and spring habitat conditions on the study area. We used growth data from a subset (n = 190) of known-aged ducklings to estimate the influence of hatch date and conspecific density on prefledging growth to help identify mechanisms underlying COEs. Prefledging growth and juvenile apparent survival were negatively related to measures of conspecific duckling density. We found evidence that detection probability varied annually for juvenile (but not adult) scaup, possibly representing decisions to delay breeding and not return to or remain at the study site in their first year of life. Like with apparent survival, there was suggestive evidence that detection probability decreased with increasing duckling density in the previous year. Hatching date was weakly negatively related to detection probability, but unrelated to apparent survival, whereas neither vital rate was related to winter ENSO index. Our results are consistent with a process where density-dependent growth rates in the prefledging period carry over to influence fitness in subsequent life-cycle stages. If this pattern generalizes to other systems, this density COE may have important implications for our understanding of duck population dynamics and reaffirms the importance of maintaining abundant brood-rearing habitats in conservation and management of ducks. © 2021 The Wildlife Society.     

Becoming pure: identifying generational classes of admixed individuals within lesser and greater scaup populations

Estimating the frequency of hybridization is important to understand its evolutionary consequences and its effects on conservation efforts. In this study, we examined the extent of hybridization in two sister species of ducks that hybridize. We used mitochondrial control region sequences and 3589 double‐digest restriction‐associated DNA sequences (ddRADseq) to identify admixture between wild lesser scaup (Aythya affinis) and greater scaup (A. marila). Among 111 individuals, we found one introgressed mitochondrial DNA haplotype in lesser scaup and four in greater scaup. Likewise, based on the site‐frequency spectrum from autosomal DNA, gene flow was asymmetrical, with higher rates from lesser into greater scaup. However, using ddRADseq nuclear DNA, all individuals were assigned to their respective species with >0.95 posterior assignment probability. To examine the power for detecting admixture , we simulated a breeding experiment in which empirical data were used to create F1 hybrids and nine generations (F2–F10) of backcrossing. F1 hybrids and F2, F3 and most F4 backcrosses were clearly distinguishable from pure individuals, but evidence of admixed histories was effectively lost after the fourth generation. Thus, we conclude that low interspecific assignment probabilities (0.011–0.043) for two lesser and nineteen greater scaup were consistent with admixed histories beyond the F3 generation. These results indicate that the propensity of these species to hybridize in the wild is low and largely asymmetric. When applied to species‐specific cases, our approach offers powerful utility for examining concerns of hybridization in conservation efforts, especially for determining the generational time until admixed histories are effectively lost through backcrossing.     

Annual survival in female white-winged scoters and lesser scaup

Quantifying survival and understanding underlying sources of variation are important for developing population models and informing management decisions. We estimated apparent survival (i.e., true survival less permanent emigration) for adult female white-winged scoters (Melanitta fusca) and lesser scaup (Aythya affinis) breeding at a northern boreal forest site in western Canada, 2002–2008. We also evaluated variation in survival relative to indices of breeding status, individual quality, spring weather conditions, local small-mammal abundance, and overwinter climate. Breeding female scoters had higher apparent survival than did nonbreeding females, suggesting that breeders had higher survival or fidelity to the study area, or that more nonbreeders were transient birds that may have bred elsewhere in subsequent years. Apparent survival rate for breeding female scoters was unrelated to other individual and environmental covariates. Nest-trapped female scaup had higher apparent survival rates than did prenesting females captured in decoy traps, implying that more pre-nesters dispersed permanently or died after marking. Nesting female scaup with higher body condition or those in years when small mammals were more abundant had higher apparent survival; associations between survival and other environmental covariates were less certain. Overall, apparent survival rate of breeding adult female scoters was lower than reported for scoters from other North American locations or for other sea duck species, whereas estimates for nesting female scaup were comparable with those from other boreal and prairie-parkland locations. Our results indicate that for scaup in this region, factors influencing female body condition, such as maintaining high-quality habitat, areas with abundant food or low disturbance, could improve annual survival. © The Wildlife Society, 2019     

Evidence for male- and juvenile-specific contact pheromones of the common bed bug Cimex lectularius

Males and females of the common bed bug, Cimex lectularius L. (Heteroptera: Cimicidae), have been shown to produce and respond to an aggregation pheromone. We tested whether juvenile C. lectularius also produce and respond to aggregation pheromone, and whether the pheromone is perceived by contact chemoreception. In dual‐choice laboratory experiments, juveniles, but not males or females, preferred juvenile‐exposed paper discs to control discs. Unlike juveniles, males and females preferred male‐exposed paper discs to control discs. Neither juveniles, males, nor females preferred female‐exposed discs to control discs. When test stimuli were inaccessible, C. lectularius failed to show any preference. Male‐ and juvenile‐specific contact pheromones may have contrasting functions of marking shelters as safe refugia for development and growth (juveniles) or mate encounter (adults), but result in the same phenomenon, the aggregation of conspecifics.     

Demography of Unexploited Beavers in Southern Illinois

ABSTRACT Beavers (Castor canadensis) are important in ecosystems and to humans. Although beavers are increasingly protected from harvest, relatively few studies of unexploited beaver populations have been reported. Furthermore, few radiotelemetry studies exist for beavers because no practical method of attaching a radiotransmitter to beavers was available until recently. We used radiotelemetry, remote videography, and trapping data to quantify survival, dispersal, and natality of unexploited beavers in southern Illinois, USA, during 2004 to 2006. Beaver colony density was one of the highest reported in the wildlife literature at 3.27 colonies/km². We monitored 62 beavers for survival; all mortalities (n = 15) occurred during the fall and winter seasons. The pooled annual survival rate for adult and juvenile females was (x̄±SE) 0.76±0.05. Annual survival rates for adult and juvenile males were 0.87±0.04 and 0.55±0.07, respectively. Seasonal survival only differed among sex classes and age classes during the fall. Dispersal rates for juvenile beavers ranged from 0.38±0.13 to 0.59±0.13 and did not vary by sex or age. To quantify natality and recruitment, we captured and euthanized 79 beavers adjacent to our live-capture area; we found a low pregnancy rate of adult females (36%), and no juveniles were bred. Natality of bred females was 3.6 offspring per adult female, and 0.36 kits were recruited per adult female. Apparent kit survival was 28%. Our research provides information to wildlife managers about beaver demographics for a high-density population, based on relatively large sample sizes and novel research techniques for the species.     

Variation in Breeding Season Survival of Female Harlequin Ducks

ABSTRACT Quantifying sources of variation in demographic rates can provide insight into processes underlying population dynamics and subsequently direct wildlife conservation. In the context of avian life history, understanding patterns of variation in survival rates of breeding females is particularly relevant because this cohort often has a disproportionately large effect on population dynamics. We estimated survival probability for 144 adult female harlequin ducks (Histrionicus histrionicus) that we marked with radiotransmitters and tracked at 4 breeding areas in western North America. Model selection results indicated both regional and temporal variation in survival rates, with most mortality attributed to predation. Cumulative survival probability (±SE) during the 100-day study period was lower at 2 sites in the Rocky Mountains of Alberta, Canada (AB1 and AB2: 0.75 ± 0.11) than in the Coast Mountains of British Columbia, Canada (BC: 0.88 ± 0.08) or the Cascade Mountains of Oregon, USA (OR: 0.89 ± 0.08). Survival also was lower during incubation than nest-initiation or brood-rearing stages at all 4 study areas. In comparison to other annual cycle stages and locations, harlequin duck mortality rates were highest on the breeding grounds, suggesting that management actions designed to reduce mortality during breeding would achieve meaningful population-level benefits.     

Survival and cause-specific mortality of male wild turkeys across the southeastern United States

Estimating survival and cause-specific mortality of male eastern wild turkeys (Meleagris gallopavo silvestris) is important for understanding population dynamics and implementing appropriate harvest management. To better understand age-specific estimates of annual survival and harvest rates, we captured and marked male wild turkeys with leg bands (n = 311) or bands and transmitters (n = 549) in Georgia, Louisiana, North Carolina, and South Carolina, USA, during 2014–2022. We fitted time to event models to data from radio-marked birds to estimate cause-specific mortality and annual survival. We used band recovery models incorporating both band recovery and telemetry data to further investigate harvest rates and survival. Annual survival from known-fate models in hunted populations was 0.54 (95% CI = 0.49–0.59) for adults and 0.86 (95% CI = 0.81–0.92) for juveniles. Cause-specific mortality analysis produced an annual harvest estimate of 0.29 (95% CI = 0.24–0.33) for adults and 0.02 (95% CI = 0.01–0.03) for juveniles, whereas predation was 0.15 (95% CI = 0.10–0.20) and 0.12 (95% CI = 0.08–0.17), respectively. Annual survival for adult males in a non-hunted population was 0.83 (95% CI = 0.72–0.97). Survival rate was negatively correlated with harvest rate, indicating harvest was an additive mortality source. Annual survival from band recovery models was 0.40 (95% CI = 0.37–0.44) for adults and 0.88 (95% CI = 0.81– 0.93) for juveniles, whereas annual harvest estimates were 0.24 (95% CI = 0.23–0.25) for adults and 0.04 (95% CI = 0.03–0.05) for juveniles. Both models suggested no differences in annual survival across years or among study areas, which included privately owned and public properties. Harvest was an additive mortality source for male wild turkeys, suggesting that managers interested in increasing annual survival of adult males could consider ways of reducing harvest rates.     

Role of kin recognition in oviposition preference and cannibalism by the predatory mite <Emphasis Type="Italic">Gynaeseius liturivorus</Emphasis>

Animals often select oviposition sites to minimize the predation risk for eggs and juveniles, which are more vulnerable to predation than adults. When females produce eggs in clusters, the eggs and juveniles are likely to suffer from cannibalism. Although cannibalism among siblings is known to be lower than among non-siblings, there have been few investigations into the possibility that females select oviposition sites that reduce the risk of cannibalism for the offspring. To test this possibility, we examined oviposition preference by adult females of the predatory mite Gynaeseius liturivorus in response to the presence of her own eggs and to eggs of other females, offering plastic discs as oviposition substrates. Although females did not clearly show a preference for plastic discs on which they had oviposited, they avoided plastic discs on which other females had oviposited. When eggs of other females were artificially placed on clean plastic discs, adult female mites avoided these discs, suggesting that the eggs were used as cues for oviposition preference. Cannibalism among juvenile siblings was lower than among non-siblings. These observations show that adult females and juveniles of G. liturivorus discriminate kin relationships among conspecific individuals. Therefore, oviposition preference by adult female G. liturivorus may lead to the reduced risk of cannibalism among offspring.     

EFFECTS OF NECK BANDS ON REPRODUCTION AND SURVIVAL OF FEMALE GREATER SNOW GEESE

Abstract: An assumption of mark-recapture studies is that the marker has no effect on the animal. Neck bands have been used extensively for goose research, but there has long been concern that they may have negative effects on some demographic parameters, and recent studies have yielded contradictory results. We evaluated the effects of neck bands on adult female greater snow geese (Chen caerulescens atlantica) by contrasting breeding propensity and apparent survival of geese marked with both a plastic neck band and a metal leg band and those marked solely with metal leg bands over an 11-year period on Bylot Island, Nunavut Territory, Canada. The use of multistate mark-recapture models also allowed us to estimate neck band loss and to obtain survival and capture probabilities that were not biased by such loss. Finally, we tested the effects of neck bands on other reproductive parameters (laying date, clutch size and nest success) over a 3-year period. Neck-banded females had decreased clutch size and capture probabilities, but their apparent survival rate, nest initiation and hatching dates, and nest survival were not affected compared to leg-banded only or unbanded females. Breeding propensity, indexed by capture probabilities of neck-banded females was, on average, 48% lower that that of leg-banded-only females but clutch size was only 10% lower. Neck band loss of females was low in this population (3% per year). We urge researchers to be cautious in the use of neck bands for estimation of population parameters and that the potential negative effects of neck bands be assessed as it is likely to be species-specific.     

Effect of Pre-Harvest Mortality on Harvest Rates and Derived Population Estimates

Banding waterfowl, in combination with the citizen science provided by hunters that report marks from harvested birds, is a long-standing, institutionalized practice for estimating probabilities of survival and exploitation (i.e., legal harvest from such populations). Range-wide population abundance can also be estimated by combining the number of banded individuals with the number harvested from the population. Waterfowl marking with uniquely identifiable bands done during late summer in North America is often referred to as pre-season banding. For example, mass capture of arctic geese for pre-season banding is normally done in July (nonbreeders) or August (failed breeders and breeders with young) during flightless molt of respective groups. An important assumption for proper inference about harvest probability provided from such samples is that there is no mortality, natural or otherwise, during the interval between when individuals are marked and when hunting seasons begin. We evaluated the effect of variable mortality that could occur between marking and subsequent hunting seasons on estimates of survival, recovery, and harvest probabilities using simulation pertinent to a typical waterfowl species. We fit a Brownie tag-recovery model to the simulated data and calculated the estimator bias that resulted from various pre-harvest mortality scenarios. There was no effect on survival probability during the interval between annual banding in subsequent years, but recovery probability, and thus estimated harvest probability, was directly and inversely related to pre-harvest mortality of juveniles. The magnitude of negative bias in harvest probability of juveniles increased further as the fraction of the population sampled declined. If the probability of pre-harvest mortality differs between marked and unmarked individuals, the negative bias in harvest probability results in overestimates of derived abundance that increases as the proportion of marked individuals in the population declines. We used our observed results to propose an explanation for occasional biologically improbable estimates of abundance of juvenile lesser snow geese (Anser caerulescens). © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Multi-scale habitat selection affects offspring survival in a precocial species

In theory, habitat preferences should be adaptive. Accordingly, fitness is often assumed to be greater in preferred habitats; however, this assumption is rarely tested and, when it is, the results are often equivocal. Habitat preferences may not directly convey fitness advantages if animals are constrained by tradeoffs with other selective pressures like predation or food availability. We address unresolved questions about the survival consequences of habitat choices made during brood-rearing in a precocial species with exclusive maternal care (mallard Anas platyrhynchos, n = 582 radio-marked females on 27 sites over 8 years). We directly linked duckling survival with habitat selection patterns at two spatial scales using logistic regression and model selection techniques. At the landscape scale (55–80 km²), females that demonstrated stronger selection of areas with more cover type 4 wetlands and greater total cover type 3 wetland area (wetlands with large expanses of open water surrounded by either a narrow or wide peripheral band of vegetation, respectively) had lower duckling survival rates than did females that demonstrated weaker selection of these habitats. At finer scales (0.32–7.16 km²), females selected brood-rearing areas with a greater proportion of wetland habitat with no consequences for duckling survival. However, females that avoided woody perennial habitats composed of trees and shrubs fledged more ducklings. The relationship between habitat selection and survival depended on both spatial scale and habitats considered. Females did not consistently select brood-rearing habitats that conferred the greatest benefits, an unexpected finding, although one that has also been reported in other recent studies of breeding birds.     

Plasma corticosterone concentrations in wild and captive juvenile tuatara (Sphenodon punctatus)

Abstract

High mortality and abnormal growth patterns commonly found in captive juvenile tuatara were hypothesised to be due in part to the effects of long‐term chronic stress of captivity. This study compared plasma concentrations of the reptilian adrenal steroid, corticosterone, in wild juvenile tuatara on Stephens Island, Cook Strait, and in captive juveniles of Stephens Island origin, held in New Zealand institutions, in February and August 1992. Seasonal variation in plasma concentration of corticosterone in wild juveniles in four seasons of the year was also examined. This is the first study of seasonal cycles in plasma corticosterone in a wild juvenile reptile. Plasma corticosterone concentrations were significantly higher in captive juvenile females (4.21 ± 0.27 ng/ml; mean ± SE) compared with wild juvenile females (2.44 ± 0.42 ng/ml) in February (P < 0.05), but not in August, and there was no difference in concentration between captive and wild juvenile males in either month. There was significant seasonal variation in plasma corticosterone in wild juvenile females (P < 0.05). However, there was no seasonal variation observed in wild juvenile males, and the magnitude of the variation in plasma corticosterone was low in both sexes (1.28 ± 0 ng/ml ‐4.65 ±3.41 ng/ml). Although mean plasma corticosterone was higher in captive juvenile females compared with wild juvenile females in February 1992, the value in captive females was within the range of mean plasma corticosterone concentrations observed in the seasonal study, and may be therefore due to asynchronicity of seasonal cycles, rather than stress. Further research is required; however, lack of correlation between plasma corticosterone concentrations and either growth rate or density indicate that captive juvenile tuatara in New Zealand are not suffering from pronounced chronic stress.     

High survival rate of a critically endangered species, the Azores Bullfinch Pyrrhula murina, as a contribution to population recovery

This paper reports analyses of a capture–mark–recapture (CMR) dataset of 149 Azores Bullfinches ringed on S?o Miguel island (Azores) between 2005 and 2007, and recaptured–resighted on a monthly basis over a 4-year period (2005–2008) throughout their breeding range. We examined the effect of time, age (adults vs. juveniles), gender (adult males and females), and environmental covariates (temperature, rainfall, NAO index) on survival probabilities. The modelling found a high and constant monthly survival probability (mean ± SE) estimated at 0.96 ± 0.01, similar between both adults and juveniles and independent of environmental conditions and gender. These findings agree with expectations from island-based life-history theory where relatively mild conditions and lack of predators should favour high survival rates to compensate for the low reproductive output. The annual survival rate was estimated at 0.62, which was also consistent with this pattern when compared with survival estimates of mainland bullfinch and passerine species on other subtropical islands obtained in similar CMR studies. Based on a canonical estimator, the size of the studied population (mean ± SE) was estimated at 1608 ± 326 individuals. Given that the population size was only around 120–400 individuals in the early 1990s, we suggest that the high survival probabilities currently applying to this critically endangered species may have substantially contributed to the recent recovery of this population. Future research studies on the species’ demography should continue to monitor survival in order to measure the effect of management interventions currently taking place within the range of the Azores Bullfinch, including the restoration of the biodiversity rich laurel forest, but also focusing on nest success, which is important for understanding population dynamics.     

Social and maternal factors affecting duckling survival in eiders Somateria mollissima

1. With the aid of a novel survivorship model, an 8-year field study of social and maternal factors affecting duckling survival in eiders (Somateria mollissima) revealed that duckling survival probability varies in accordance with maternal brood-rearing strategy. This variability in survival provides compelling evidence of different annual fitness consequences between females that share brood-rearing and those that tend their broods alone. Consequently, as prebreeding survival is often a major source of individual variation in lifetime reproductive success, a female's annual, state-dependent (e.g. condition) choice of a brood-rearing strategy can be a critical fitness decision. 2. Variance in duckling survival among lone tender broods was best explained by a model with significant interannual variability in survival, and survivorship tending to increase with increasing clutch size at hatch. Clutch size was correlated positively with female condition. Hatch date and female body condition together affected duckling survival, but their contributions are confounded. We were unable to identify a relationship between female age or experience and duckling survival. 3. Variance in duckling survival among multifemale brood-rearing coalitions was best explained by a model that included the number of tenders, the number of ducklings and interannual variation in how their ratio affected survivorship. Hatch date did not significantly influence survival. 4. Expected duckling survival is higher in early life for lone tenders when compared with multifemale brood-rearing coalitions. However, as ducklings approach 2-3 weeks of age, two or three females was the optimal number of tenders to maximize daily duckling survival. The survivorship advantage of multifemale brood-rearing coalitions was most evident in years of average survival. 5. The observed frequency distribution of female group sizes corresponds with the distribution of offspring survival probabilities for these groups. Evidence for optimal group sizes in nature is rare, but the most likely candidates may be groups of unrelated animals where entry is controlled by the group members, such as for female eiders. 6. Our study demonstrates that differences in social factors can lead to different predictions of lifetime reproductive success in species with shared parental care of self-feeding young.     

Adaptive significance of maternal induction of density-dependent phenotypes

Density has been demonstrated to impact life history traits such as growth, fecundity and survival. Some authors have proposed that morphological and behavioral traits have evolved in response to density conditions. To escape the adverse effect of density, individuals can either adapt to crowding or avoid crowding by dispersing. The aim of this work is to study the interplay between local adaptation and dispersal in four populations of the common lizard, Lacerta vivipara, where densities of both the maternal and juvenile environment have been experimentally manipulated. Density was decreased in the spring by removing a quarter of the population at two sites and was un-manipulated in two other sites. One month later, we caught some pregnant females and kept them in the laboratory until parturition. To manipulate density of postnatal neonates and juveniles, we divided each clutch into two, and released half of the juveniles either in a reduced density site or in a control one. We then recaptured individuals a year after release and recorded their size and weight. When density was reduced, females increased their clutch size, but produced offspring of lower body condition than in the control sites. The conspicuous ventral color of females was likewise increased when density was reduced. However, offspring growth rate, local survival and dispersal were not influenced by maternal density. Juvenile females released in the reduced-density site had lower survival rate than those released in the control density site. Contrary to expectations, offspring dispersal was significantly higher at the reduced compared to control density sites. There was no interaction between maternal density habitat and the juvenile release habitat indicating that maternal effects did not influence juvenile life history traits in a different way according to the level of density. Moreover, clutch size and offspring size had no effect on juvenile growth or survival.     

Variation in the Diet of Ducks During Spring Migration

Because management practices that promote the production of plant foods may differ from management practices that promote the production of aquatic invertebrates, a thorough understanding of the diet is needed to develop management strategies for various stages of the annual cycle for dabbling and diving ducks. Diet of dabbling (tribe Anatini) and diving (tribe Aythyini) ducks during breeding, autumn migration, and winter has been documented. Our goal was to estimate and compare the diet of blue-winged teal (Spatula discors), gadwall (Mareca strepera), mallard (Anas platyrhyncos), lesser scaup (Aythya affinis), and ring-necked duck (Aythya collaris) during spring migration in the Mississippi Flyway in the United States and evaluate variation among species. We collected 919 ducks for diet analysis from multiple wetlands at 6 sites across 4 states during the spring migration of 2006 and 2007. We collected ≥10 individuals of each species at each of the 6 study sites except we collected only 1 gadwall at the Scioto River site and 2 lesser scaup at the Cache River site. We detected that the proportion of plant and animal material in foods of each spring migrating duck species was in general intermediate of that found in wintering and breeding birds. Furthermore, the proportion of plant and animal material in the diet of species varied even among closely related species, indicating species are partitioning food sources along a protein-carbohydrate gradient during spring migration. We recommend that resources for ducks be managed to provide diverse wetlands to support the varied diets of even closely related species. © 2021 The Wildlife Society.     

Seasonal variation in pre‐fledging survival of lesser scaup Aythya affinis: hatch date effects depend on maternal body mass

Among temperate‐breeding birds, offspring survival and reproductive success are often inversely related to timing of breeding. The mechanisms that produce seasonal declines in offspring survival are not fully understood but may be related to temporal changes in parental quality, environmental quality, or both. We analyzed data for lesser scaup Aythya affinis to evaluate hypothesized effects of parental quality and date on pre‐fledging survival. Maternal quality, as indexed by body mass, did not have an independent effect on offspring survival in this species. Maternal body mass did not decline seasonally and did not have an independent effect on duckling survival. Although we did not detect an independent effect of hatch date on duckling survival, duckling survival declined seasonally for broods raised by lightweight females, indicating an interactive effect of maternal mass and date. We hypothesize that this interaction may be driven by seasonally declining food resources coupled with the influence of female condition on the ability to monopolize food resources or remain attentive to the brood. We also tested morphological predictions of the date hypothesis by examining physical characteristics of ducklings. When corrected for age and size, late‐hatched ducklings tended to have marginally larger digestive systems and smaller leg muscles than did early‐hatched birds. Abundances of intestinal parasites acquired through diet decreased marginally in late‐hatched ducklings. Results for digestive system and parasite infection patterns suggested that later‐hatched broods may shift diets, consistent with a contribution of environmental factors to seasonal variation in offspring survival. Taken together, our results suggest that both female attributes and environmental conditions may influence seasonal patterns of offspring survival in this species.