ABSTRACT Correlations between annual recovery and survival probabilities estimated from tag‐recovery data have been used to quantify the demographic response of exploited populations to harvest. Deane et al. (2023) evaluated the bias and certainty of correlation parameters between recovery and survival probabilities estimated as random effects drawn from bivariate normal distributions relative to different prior distributions and sample size combinations. Riecke et al. (2024) observed that we incorrectly parameterized a precision matrix with Gamma priors and suggested using a Gamma(1,1) prior distribution for the standard deviations as an alternative. Riecke et al. (2024) provided results from tag‐recovery models that estimate mortality hazard rates after fitting these models to tag‐recovery datasets with large sample sizes. Here, we fit tag‐recovery models to the data we previously simulated (Deane et al. 2023) while using Gamma(1,1) as the prior distribution for standard deviations while parameterizing these models to estimate recovery and survival in discrete time or to estimate cause‐specific mortality as hazard rates. We compare our new results to previous results obtained while using Uniform(0,5) prior distribution for the standard deviations. When sample sizes were large, correlation estimates obtained with either prior distribution provided similarly reliable parameter recovery and inference, replicating results of Riecke et al. (2024). With smaller sample sizes similar to those available for most duck populations in North America, correlations estimated with either prior distribution were uncertain and ambiguous. With decreasing sample sizes, annual survival was estimated with increasing uncertainty when compared to annual recovery, likely contributing to the poor ability to estimate correlation. Consistent with the original interpretation of Deane et al. (2023) and previous literature, we found correlations were often estimated with high uncertainty such that the sign (+ or –) may be the only attribute of these parameters that can be reliably interpreted.

Recent empirical studies have quantified correlation between survival and recovery by estimating these parameters as correlated random effects with hierarchical Bayesian multivariate models fit to tag-recovery data. In these applications, increasingly negative correlation between survival and recovery has been interpreted as evidence for increasingly additive harvest mortality. The power of these hierarchal models to detect nonzero correlations has rarely been evaluated, and these few studies have not focused on tag-recovery data, which is a common data type. We assessed the power of multivariate hierarchical models to detect negative correlation between annual survival and recovery. Using three priors for multivariate normal distributions, we fit hierarchical effects models to a mallard (Anas platyrhychos) tag-recovery data set and to simulated data with sample sizes corresponding to different levels of monitoring intensity. We also demonstrate more robust summary statistics for tag-recovery data sets than total individuals tagged. Different priors led to substantially different estimates of correlation from the mallard data. Our power analysis of simulated data indicated most prior distribution and sample size combinations could not estimate strongly negative correlation with useful precision or accuracy. Many correlation estimates spanned the available parameter space (-1,1) and underestimated the magnitude of negative correlation. Only one prior combined with our most intensive monitoring scenario provided reliable results. Underestimating the magnitude of correlation coincided with overestimating the variability of annual survival, but not annual recovery. The inadequacy of prior distributions and sample size combinations previously assumed adequate for obtaining robust inference from tag-recovery data represents a concern in the application of Bayesian hierarchical models to tag-recovery data. Our analysis approach provides a means for examining prior influence and sample size on hierarchical models fit to capture-recapture data while emphasizing transferability of results between empirical and simulation studies.

Hibernation is associated with long lifespan: on average, hibernating mammals live 15% longer than nonhibernators of equivalent mass. We investigated how survival varies with sex, season, and the deployment of biologgers in arctic ground squirrels (Urocitellus parryii (Richardson, 1825)), a widely distributed northern hibernator. The duration of hibernation in arctic ground squirrels differs markedly by sex: females hibernate 30% longer each year than males, a behavioural trait that could positively affect female survival. Additionally, males engage in aggressive territorial and food cache defense in spring and fall, which may decrease survival in this sex. From 13 years of mark–recapture data, we estimated apparent survival of arctic ground squirrels in Arctic Alaska (USA) using Cormack–Jolly–Seber models in program MARK. We found that females had higher annual survival ([Formula: see text] (95% confidence interval (CI): 0.469, 0.913)) than males ([Formula: see text] (95% CI: 0.416, 0.670)), with a maximum observed lifespan (10 years) that exceeded that of males (6 years). We also show that biologger use and implantation did not significantly impact survival. Quantifying basic arctic ground squirrel demographics from this well-studied population illustrates how sex-specific hibernation parameters may influence lifespan differences in male and female arctic ground squirrels and provides support for the safety of biologging devices.

AbstractInforming conservation and management decisions for habitats frequented by species of high management interest often face the challenge of limited resources for conducting wildlife surveys. When surveys are focused on local areas or sparsely distributed species, it may also be difficult to obtain counts sufficient for implementing abundance models that account for imperfect detection. With replicated aerial surveys collected within a 70.25‐km2portion of the Eastern Alaska Range, Alaska, USA, during the summers of 2013–2015, we estimated daily abundance of Dall’s sheep using two different estimation methods: BayesianN‐mixture models and Poisson regression models. We then compared estimates of relative abundance from both model types while paying special attention to the assumption of closure within individual survey units. With abundance estimates obtained from individual survey days, we then estimated the average number of Dall’s sheep within the survey area for the period 1 July–1 October. Daily ewe abundance followed a quadratic pattern, with 10–20 ewes being within our survey area in early July and late September, and approximately 90 ewes within the survey area in mid‐August. Lamb‐to‐ewe ratios averaged 0.2 from July–September, while ram‐to‐ewe ratios averaged 0.4 from July until mid‐August before increasing to about 1.0 by the end of September. These results indicate that our survey area is an important habitat to local Dall’s sheep populations when lambs are vulnerable to predators. Accordingly, human recreation and military training within the survey area should be minimized 1.5–3.0 months after parturition to minimize disturbance. We also found thatN‐mixture models displayed a pattern of abundance estimates that increased in magnitude as model complexity increased. We thus recommend an a priori approach toN‐mixture model construction that balances the risk of overfitting models to modest data against the risk of fitting models that do not explain heterogeneity in abundance and detection probability. Lastly, we suggest simple improvements to replicated, aerial surveys for species like Dall’s sheep focused on reducing violations of the closure assumption within individual survey units, which can reduce bias of density estimates obtained withN‐mixture models.

ABSTRACT Nasal discs have been used to identify ducks in studies of survival and reproduction. To date, there has not been a comprehensive assessment of nasal‐disc effects on the vital rates of wild ducks. We applied nasal discs to 603 juvenile and 784 adult lesser scaup ( Aythya affinis ) females from a population breeding in southwest Montana, USA, and released 1,399 juvenile and 71 adult females wearing only metal leg bands between June 2005 and September 2016. Using resighting, recapture, and hunter‐recovery data collected from those individuals, we estimated survival and recovery probability with multistate capture‐recapture models in Program MARK. We also assessed if recovery distance from our study site and pre‐breeding and brood‐rearing body condition were diminished for females wearing nasal discs. Model‐averaged survival probabilities were 0.231 ± 0.035 (SE) for juveniles and 0.482 ± 0.019 for adults released with nasal discs. Survival was 1.8–3.4 times higher for females released with metal leg bands when compared to those released with nasal discs; survival of these juveniles was 0.433 ± 0.049 and 0.693 ± 0.039 for adults. We did not find evidence for recovery probability or recovery distance varying between females that wore nasal discs and those that did not. During the pre‐breeding and brood‐rearing seasons, we did not find females wearing nasal discs to be in lower body condition when compared to unmarked females. Our comprehensive assessment of nasal discs on wild lesser scaup suggests that survival probabilities estimated from nasal‐marked study populations should be cautiously interpreted as minimum estimates. © 2021 The Wildlife Society.

ABSTRACT 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.

Since the mid-to-late 1990s, lesser scaup (Aythya affinis) populations have remained more than 20% below the population goal set forth in the North American Waterfowl Management Plan. Accordingly, considerable attention has been directed towards understanding what factors may be limiting their population, including the role of harvest. Red Rock Lakes National Wildlife Refuge (RRL) in southwestern Montana is the site of a long-term study of lesser scaup ecology and demography. Preliminary harvest estimates indicate that this population is harvested at rates similar to the continental population with juveniles experiencing an annual average harvest rate of 9.1% (95% CI = 7.7 - 10.7%) and adults an average annual harvest rate of 3.6% (95% CI = 2.2 - 6.1%). Since 2005, ~1,300 female have been banded on the study site and an additional ~1,000 females have been nasal-marked. In addition, ~1,400 resightings have been collected for nasal-marked hens on the study site and ~340 dead recoveries from our study population have been reported from Canada to Mexico. With results obtained from multistrata models that utilize these multiple encounter types, I will present (1) estimates of harvest and natural mortality rates for female lesser scaup banded and nasal-marked at RRL from 2005-2016; (2) how non-harvest mortality varies in relation to harvest mortality over the same period; (3) an assessment of how these rates respond to changes in hunting regulations. These results will be used to help inform lesser scaup harvest demography, a key structural uncertainty in current harvest models identified in the draft Scaup Conservation Action Plan.