Capture Mark Recapture Models Research Articles

Long‐term trends in abundance and recruitment of Shortnose Sturgeon in the Altamaha River, Georgia

AbstractObjectiveThe objective of this study was to estimate the population size and annual recruitment of Shortnose Sturgeon Accipenser brevirostrum in the Altamaha River estuary in Georgia, United States, during an 11‐year period. The Shortnose Sturgeon is an endangered fish species that occupies rivers on the east coast of North America. Previous studies have suggested that the Altamaha River supports the largest population of Shortnose Sturgeon in the southern United States; however, the status of the population has not been assessed in 11 years.MethodsWe used entanglement gears to capture Shortnose Sturgeon in the Altamaha River estuary, marked them, and used an established statistical method (closed‐population capture–mark–recapture models) to annually estimate total population size and age‐1 recruitment from 2012 to 2022.ResultWe were able to estimate the size of age‐1 cohorts in 7 of the 11 years of data collection. Point estimates of annual age‐1 recruitment varied between 113 and 1021 individuals, and total population size varied between 452 (95% confidence interval [CI]: 116–2277) and 5054 individuals (95% CI: 2155–13,267).ConclusionRecruitment of age‐1 juveniles was variable, suggesting that reproduction success is inconsistent between years in the Altamaha River. The results of this study, in combination with previous work, do not show any clear trends in Altamaha River Shortnose Sturgeon population abundance or recruitment. The population seems to be stable, but in the absence of historical population numbers, it is unclear whether the population should be considered recovered or is stagnated in its recovery.

Demographic insights for the endangered Apennine yellow-bellied toad in the Pollino National Park (Southern Italy). A five-year Capture-Mark-Recapture study

Investigating population structure, parameters, and growth over time is vital for conserving endangered taxa like the Apennine yellow-bellied toad (Bombina variegata pachypus) in Italy. The Apennine yellow-bellied toad faces habitat loss or degradation, disease, and climate change threats. Our study delves into the population dynamics of this endemic amphibian by monitoring populations in two breeding sites within the Pollino National Park (Southern Italy) using a five-year Capture-Mark-Recapture (CMR) approach. With a particular emphasis on demographic parameters such as population size, detectability, survival, temporary emigration probability, and body condition index, the research aims to contribute to understanding population dynamics and inform conservation efforts. We used two CMR models to estimate these parameters: Jolly-Seber with POPAN parametrisation and Pollock's robust design with Huggins' estimator. Results showed variation in body size between males and females, challenging previous findings in south-central Italy. For both populations, demographic data indicate high annual adult survival, fidelity to the breeding areas, support for no movement, and minimal trap response. Abundance over the years reveals a slight decline in one site and a gradual increase in the other. The estimated maximum population size indicated ∼ 92 animals in one population and ∼ 70 in the other one. Despite the high conservation concern for the Apennine yellow-bellied toad, there remains a dearth of quantitative information on demographic aspects in Southern Italy. The findings underscore the importance of protected areas in biodiversity conservation and contribute to understanding the B. v. pachypus conservation status, suggesting that small, isolated populations may be vulnerable to unpredictable fluctuations, inbreeding depression, and extinction risks. Additionally, the research emphasises the importance of long-term CMR studies to gain insights into population dynamics and develop effective conservation strategies and management practices, particularly in the face of climate changes that may impact both the endemic taxon and its habitat.

High Mortality of Wild European Rabbits during a Natural Outbreak of Rabbit Haemorrhagic Disease GI.2 Revealed by a Capture-Mark-Recapture Study

Rabbit haemorrhagic disease virus (RHDV) GI.2 has caused significant declines in the abundance of wild European rabbits (Oryctolagus cuniculus), contributing to the species being recently classified as “endangered” in its native range. The epidemiology of this virus is still poorly understood despite its relevance for domestic and wild rabbits. During a longitudinal capture-mark-recapture (CMR) study of wild Iberian rabbits, O. c. algirus, in a semiextensive breeding enclosure, an outbreak of RHDV GI.2 took place in January-February 2022, allowing us to estimate key epidemiological parameters of a natural outbreak. From April 2021 to July 2022, 340 rabbits were captured 466 times and individually identified, and some were vaccinated against myxoma virus (MYXV) and/or RHDV GI.2. Sera were collected and tested for IgG specific for MYXV and RHDV GI.2, and data were analyzed using multievent CMR models. During six weeks in January-February 2022, an estimated 81.0% (CI95 77.1–84.3%) of the population died. Intensive aboveground searches could recover 189 carcasses (50.5% of the estimated mortality, CI95 41.8–63.4%), with RHDV GI.2 detected in 6/7 tested. Apparent RHDV GI.2 seroprevalence rose from 15.4% (CI95 8.0–27.5%) in January 2022 to 87.9% (CI95 72.7–95.2%) in February 2022. The apparent mortality of RHDV GI.2-seropositive rabbits during the outbreak was estimated as null, while for seronegative rabbits, it was 76.0% (CI95 53.8–90.3%). Among the seronegative rabbits, mortality was higher in unvaccinated (100%) than in recently vaccinated (60.0 ± 16.6%) and in females (100%) than in males (52.0 ± 17.1%). Infected carcasses in the burrows might explain the medium-term disease persistence in the population following the outbreak. Rabbits with antibodies at the cutoff for seropositivity were fully protected from fatal infection. Females had a higher fatality rate than males, underscoring the impact of RHDV GI.2 on the population dynamics of this endangered species.

Does coat colour influence survival? A test in a cyclic population of snowshoe hares.

Some mammal species inhabiting high-latitude biomes have evolved a seasonal moulting pattern that improves camouflage via white coats in winter and brown coats in summer. In many high-latitude and high-altitude areas, the duration and depth of snow cover has been substantially reduced in the last five decades. This reduction in depth and duration of snow cover may create a mismatch between coat colour and colour of the background environment, and potentially reduce the survival rate of species that depend on crypsis. We used long-term (1977-2020) field data and capture-mark-recapture models to test the hypothesis that whiteness of the coat influences winter apparent survival in a cyclic population of snowshoe hares (Lepus americanus) at Kluane, Yukon, Canada. Whiteness of the snowshoe hare coat in autumn declined during this study, and snowshoe hares with a greater proportion of whiteness in their coats in autumn survived better during winter. However, whiteness of the coat in spring did not affect subsequent summer survival. These results are consistent with the hypothesis that the timing of coat colour change in autumn can reduce overwinter survival. Because declines in cyclic snowshoe hare populations are strongly affected by low winter survival, the timing of coat colour change may adversely affect snowshoe hare population dynamics as climate change continues.

Spawning Atlantic cod (Gadus morhua L.) exposed to noise from seismic airguns do not abandon their spawning site

Abstract Seismic airgun surveys may disturb and displace fish at large ranges. If such displacement causes fish to abandon spawning grounds, reproductive success could be impacted. To investigate whether airgun sound causes cod (Gadus morhua L.) to leave their spawning grounds, acoustic telemetry arrays were deployed on two cod spawning grounds: a test and a reference site. From 2019 to 2021, 136 mature cod from the test site and 45 from the reference site were tagged with acoustic transmitters. Intermittent seismic shooting of two 40 in.3 airguns for 1 week during the spawning periods of 2020–2021 resulted in fluctuating sound exposure levels (SEL) at the test site, comparable to a full-scale industrial survey 5–>40 km away. Residency and survival of tagged cod were analysed with capture–mark–recapture models fitted to the detection and recapture data. Departure rate of the mature cod varied between spawning seasons but was similar between the test and reference sites. Neither survival nor departure significantly differed between seismic exposure and baseline periods. The results indicated that exposure to airguns at received SEL of up to ∼145 dB re 1 µPa2 s, comparable to a seismic survey occurring several kilometres away, did not displace tagged cod from spawning grounds.

New methods to derive sea turtle nester abundance from nest counts: Ground truthing and the bias of current approaches

Abundance is a key parameter for characterizing animal populations of conservation concern. In sea turtles, annual clutch counts represent the most common population index. When the number of annual nesting females (ANF) is sought, clutch frequency (CF; average number of clutches laid per female) is used as a conversion factor. Here we assess the performance of five current methods for estimating ANF and of two new methods based on the interdependence of nesting activity parameters, investigated through a Monte Carlo approach with generalized additive models. All methods were evaluated on virtual populations and on a unique case of empirical data from a sea turtle population with a known ANF based on genetic identification of clutches (Caretta caretta, Northern Recovery Unit, USA). Results show that current methods produce errors often greater than the simple count of nesting females directly encountered, except for a capture-mark-recapture (CMR) model. One of the new methods takes advantage of both nest count and CMR data and shows the best performance at a wide range of detection probabilities. The second new method is based on nest count data only and can provide at least an approximate estimate of ANF where no CMR data are available. Our findings can dramatically improve sea turtle population abundance estimates worldwide. We recommend abandoning the use of any CF estimate as a direct conversion factor in favor of implementing the CMR model and the new methods to improve current estimates and to provide estimates where limited data have prevented doing so previously.

Estimating density of ocelots in the Atlantic Forest using spatial and closed capture–recapture models

Abstract Monitoring variation in population features such as abundance and density is essential for evaluating and implementing conservation actions. Camera trapping can be important for assessing population status and trends and is increasingly used to generate density estimates through capture–recapture models. Moreover, success in using this technique can vary seasonally given shifting animal distributions and camera encounter rates. Notwithstanding these potential advantages, a gap still exists in our understanding of the performance of such models for estimating density of cryptic Neotropical terrestrial carnivores with low encounter rate probability with cameras. In addition, scanty information is available on how sampling design can affect the accuracy and precision of density estimates for Neotropical carnivores. We evaluate the performance of spatially explicit versus nonspatial capture–mark–recapture models for estimating densities and population size of ocelots (Leopardus pardalis) within an Atlantic Forest fragment in Brazil. We conducted two spatially concurrent surveys, a random camera-trap deployment covering the entire study area and a systematic camera-trap deployment in a small portion of the study area, where trails and unpaved roads were located. We obtained 244 photographs of ocelots in the Rio Doce State Park from April 2016 to November 2017, using 54-double camera stations spaced approximately 1.5 km apart (random placement) totaling 4,320 trap-nights and 15-double camera stations spaced from 0.3–10 km apart (systematic placement) totaling 1,200 trap-nights. Using the random placement design, ocelot density estimates were similar during the dry season, 14.0 individuals/km2 (± 5.6 SE, 6.6–30.0, 95% CI) and 13.78 individuals/km2 (± 4.25 SE, 5.4–22.1, 95% CI) from spatially explicit capture–recapture and nonspatial models, respectively. Using the systematic placement design spatially explicit models had smaller and less precise ocelot density estimates than nonspatial models during the dry season. Ocelot density was 12.4 individuals/100 km2 (± 5.0 SE, 5.8–26.7, 95% CI) and 19.9 individuals/km2 (± 5.2 SE, 9.7–30.1, 95% CI) from spatially explicit and nonspatial models, respectively. During the rainy season, we found the opposite pattern. Using the systematic placement design, spatial-explicit models had higher and less precise estimates than nonspatial models. Ocelot density was 24.6 individuals/100 km2 (± 13.9 SE, 8.7–69.4, 95% CI) and 11.89 individuals/km2 (± 3.93 SE, 4.19–19.59, 95% CI) from spatially explicit and nonspatial models, respectively. During the rainy season, we could not compare models using the random placement design due to limited number of recaptures to run nonspatial models. In addition, a single recapture yielded an imprecise population density estimate using spatial models (high SE and large 95% CIs), thus precluding any comparison between nonspatial and spatially explicit models. We demonstrate relative differences and similarities between the performance of spatially explicit and nonspatial capture–mark–recapture models for estimating density and population size of ocelots and highlight that both types of capture–recapture models differ in their estimation depending on the sampling design. We highlight that performance of camera surveys is contingent on placement design and that researchers need to be strategic in camera distribution according to study objectives and logistics. This point is especially relevant for cryptic or endangered species occurring at low densities and having low detection probability using traditional sampling methods.

Pulsed resources and the resource‐prediction strategy: a field‐test using a 36‐year study of small mammals

Pulsed resource environments are known for their marked variations in resource availability over space and time. Animals living in such environments usually increase reproduction after resources become available. Some small mammal populations, however, may use environmental cues that precede large crops of seeds (e.g. pollen, flowers, unripe seeds) to ‘predict' mast‐seeding events and reproduce in advance. In other words, these populations exhibit a resource‐prediction strategy based on future fitness prospects. Habitat selection might play a key role in the resource‐prediction strategy, but our understanding of habitat selection in pulsed resource environments is extremely limited. We used a 36‐year dataset on small mammal trapping and seed availability collected in Maine (USA) to test if American red squirrels Tamiasciurus hudsonicus, eastern chipmunks Tamias striatus, white‐footed mice Peromyscus leucopus and southern red‐backed voles Myodes gapperi select habitats based on upcoming resources and examine the consequences to individual fitness. Small mammal trapping was conducted in summer before seeds were available, thus trapping occurred when only the cues of an upcoming mast event were available. Using home‐range estimations and capture data, we performed resource selection analyses to assess if individuals select habitat to maximize future resource acquisitions. Using capture–mark–recapture models, we also estimated individual survival (a proxy for fitness). Our results do not support habitat selection as a mechanism underlying the resource‐prediction hypothesis, indicating that individuals do not select habitats based on the upcoming seed availability. Nevertheless, we found that white‐footed mice with home ranges in areas characterized by a greater quantity of white oak acorns have up to a 15% higher survival rate. Our empirical study advances the understanding of predator response to pulsed resources by not supporting a key mechanism thought to underpin the anticipatory responses that have been observed in many ecosystems worldwide.

A comparison of capture-mark-recapture and camera-based mark-resight to estimate abundance of Alpine marmot (Marmota marmota)

Obtaining reliable estimates of population abundance is of utmost importance for wildlife research and management. To this aim, camera-traps are increasingly used, as this method has the advantage of being noninvasive and allows for continuous monitoring. Camera traps can be used to estimate abundance in combination with traditional capture-recapture techniques, as well as with estimators that do not require marked individuals. Here, we investigated the use of camera-based mark-recapture methods applied to an Alpine marmot (Marmota marmota) population in the Paneveggio-Pale di San Martino Natural Park (eastern Italian Alps). We compared abundance estimates derived from a traditional capture-mark-recapture (CMR) framework and camera trap mark-resight (CTMR) over three consecutive years. CMR models estimated a population size of n = 19 individuals (95% CI = 18-27), n = 15 (14-22) and n = 24 (22-32) in 2019, 2020 and 2021 respectively. CTMR returned an estimated population size of n = 24 (95% CI = 18-30), n = 20 (17-24) and n = 22 (21-24) for the same years. The difference between the estimate of these two methods was significant only in 2020, with CMR returning a lower estimate than CTMR (95% CI = –9.4–0.6). This difference was not significant for 2019 (95% CI = –10.9-0.9) and 2021 (95% CI = –1.8-5.9). Based on our results, the use of CTMR techniques is promising in the estimation of absolute population size of marmots, and the estimator was slightly more precise than CMR. Further studies are needed to evaluate the effectiveness of CTMR with reduced capture effort.

Are behaviour and stress-related phenotypes in urban birds adaptive?

Urbanisation is a world‐wide phenomenon converting natural habitats into new artificial ones. Environmental conditions associated with urbanisation represent great challenges for wildlife. Behaviour and stress tolerance are considered of major importance in the adaptation to novel urban habitats and numerous studies already reported behavioural and stress response phenotypes associated with urbanisation, often suggesting they represented adaptations, while rarely demonstrating it.The main goal of this study was to test the adaptive nature of urban shifts in behavioural and stress‐related traits, and by adaptive we mean phenotypic change favouring traits in the same direction as selection.Using 7 years of monitoring of urban and forest great tits, we first tested for differences in exploratory behaviour, aggressiveness and breath rate, between both habitats. Second, we performed habitat‐specific analyses of selection on the three former traits using (a) reproductive success and (b) survival estimated via capture–mark–recapture models, as fitness estimates, to determine whether shifts in these behavioural and stress‐related traits were aligned with patterns of ongoing selection.We found that urban birds displayed higher exploratory behaviour and aggressiveness, and higher breath rate, compared to forest birds. Selection analyses overall revealed that these shifts were not adaptive and could even be maladaptive. In particular, higher handling aggression and higher breath rate in urban birds was associated with lower fitness. Higher exploration scores were correlated with lower survival in both habitats, but higher reproductive success only in forest males. Overall, differences in patterns of selection between habitats were not consistent with the phenotypic divergence observed.Taken together, these results highlight that phenotypic shifts observed in cities do not necessarily result from new selection pressures and could be maladaptive. We hypothesise that divergences in behavioural traits for urban birds could result from the filtering of individuals settling in cities. We thus encourage urban evolutionary scientists to further explore the adaptive potential of behavioural traits measured in urban habitats (a) by replicating this type of study in multiple cities and species, (b) by implementing studies focusing on immigrant phenotypes and (c) by measuring selection at multiple life stages.

Increasing numbers of killer whale individuals use fisheries as feeding opportunities within subantarctic populations.

Fisheries can generate feeding opportunities for large marine predators in the form of discards or accessible catch. How the use of this anthropogenic food may spread as a new behaviour, across individuals within populations over time, is poorly understood. This study used a 16-year (2003-2018) monitoring of two killer whale Orcinus orca subantarctic populations (regular and Type-D at Crozet), and Bayesian multistate capture-mark-recapture models, to assess temporal changes in the number of individuals feeding on fish caught on hooks ('depredation' behaviour) of a fishery started in 1996. For both populations, the number of depredating individuals increased during the study period (34 to 94 for regular; 17 to 43 for Type-D). Increasing abundance is unlikely to account for this and, rather, the results suggest depredation was acquired by increasing numbers of existing individuals. For regular killer whales, a plateau reached from 2014 suggests that it took 18 years for the behaviour to spread across the whole population. A more recent plateau was apparent for Type-Ds but additional years are needed to confirm this. These findings show how changes in prey availability caused by human activities lead to rapid, yet progressive, innovations in killer whales, likely altering the ecological role of this top-predator.

The need for long-term population monitoring of the world’s largest fish

Many large marine species are vulnerable to anthropogenic pressures, and substantial declines have been documented across a range of taxa. Many of these species are also long-lived, have low individual resighting rates and high levels of individual heterogeneity in capture probability, which complicates assessments of their conservation status with capture-�mark-�recapture (CMR) models. Few studies have been able to apply CMR models to whale sharks Rhincodon typus, the world’s largest fish. One of their aggregation sites off Mafia Island in Tanzania is characterised by unusually high residency of this Endangered species, making it an ideal target for CMR methods. Three different CMR models were fitted to an 8 yr photo-identification data set to estimate abundance, population trend and demographic parameters. As anticipated, resighting rates were unusually high compared to other aggregations. Different CMR models produced broadly similar parameter estimates, showing a stable population trend with high survivorship and limited recruitment. Tagging and biopsy sampling for concurrent research did not negatively affect those sharks’ apparent survival or capture probabilities. Scenario-based power analyses showed that only pronounced abundance trends (±30%) would be detectable over our study period, at a 90% level of probability, even with the relatively high precision in yearly abundance estimates achieved here. Other, more transient whale shark aggregations, with reduced precision in abundance estimates, may only be able to confidently detect a similar trend with CMR models after 15-20 yr of observations. Precautionary management and long-term monitoring will be required to assist and document the recovery of this iconic species.

Estimating abundance, temporary emigration, and the pattern of density dependence in a cyclic snowshoe hare (Lepus americanus) population in Yukon, Canada

Estimates of demographic parameters based on capture–mark–recapture (CMR) methods may be biased when some individuals in the population are temporarily unavailable for capture (temporary emigration). We estimated snowshoe hare abundance, apparent survival, and probability of temporary emigration in a population of snowshoe hares (Lepus americanus Erxleben, 1777) in the Yukon (Canada) using Pollock’s robust design CMR model, and population density using spatially explicit CMR models. Survival rates strongly varied among cyclic phases, seasons, and across five population cycles. We found strong evidence that temporary emigration was Markovian (i.e., nonrandom), suggesting that it varied among individuals that were temporary emigrant in the previous sampling period and those that were present in the sampled area. The probability of temporary emigration for individuals that were in the study area during the previous sampling occasion (γ″) varied among cycles. Probability that individuals that were temporarily absent from the sampled area would remain temporary emigrants (γ′) showed strongly seasonal pattern, low in winter and high during summers. Snowshoe hare population density ranged from 0.017 (0.015–0.05) hares/ha to 4.43 (3.90–5.00) hares/ha and showed large-scale cyclical fluctuations. Autocorrelation functions and autoregressive analyses revealed that our study population exhibited statistically significant cyclic fluctuations, with a periodicity of 9–10 years.

Effects of timber harvest on survival and movement of stream salamanders in a managed forest landscape

AbstractWith escalating anthropogenic alteration of landscapes worldwide, managed forests are increasingly important as providers of ecosystem services and wildlife habitat. Therefore, it is crucial to maintain a balance between producing forest products and biodiversity conservation. Several studies have reported negative effects of forest management on terrestrial plethodontid salamanders, but fewer have focused on stream‐dwelling species or evaluated mechanisms for shifts in their abundance (e.g., mortality vs. movement). We used a before–after–control–impact design to examine the effects of clear‐cut harvesting on a semi‐aquatic stream‐breeding salamander endemic to the Ouachita Mountains, Desmognathus brimleyorum. We conducted a three‐year capture–mark–recapture (CMR) study at three streams within a managed pine (Pinus spp.) landscape in west‐central Arkansas, USA. Loblolly pine (Pinus taeda) stands surrounding two of the streams were clear‐cut (leaving a 14–21 m wide forested buffer on each side of the stream) midway through the study; the third stream served as a control site and remained unharvested. We estimated apparent survival using open CMR models and compared salamander movement over time and between harvested and control streams. Overall, our models revealed seasonal and temporal variation in salamander survival and abundance, but little evidence for strong immediate effects of timber harvesting on post‐metamorphic salamanders within two years postharvest. However, there was increased salamander movement at sites where forest harvest occurred. Our results suggest that streamside buffers of at least 14–28 m on either side of a stream are effective for minimizing immediate effects of forestry activities on juvenile and adult stream‐dwelling salamanders, when timber harvest occurs in the winter months. These results will inform management decisions aimed at conserving biodiversity and ecosystem integrity in managed forest landscapes while also filling a critical gap in the knowledge of stream salamander demographic parameters.

Effects of snake fungal disease on short-term survival, behavior, and movement in free-ranging snakes.

Pathogenic fungi are increasingly associated with epidemics in wildlife populations. Snake fungal disease (SFD, also referred to as Ophidiomycosis) is an emerging threat to snakes, taxa that are elusive and difficult to sample. Thus, assessments of the effects of SFD on populations have rarely occurred. We used a field technique to enhance detection, Passive Integrated Transponder (PIT) telemetry, and a multi-state capture-mark-recapture model to assess SFD effects on short-term (within-season) survival, movement, and surface activity of two wild snake species, Regina septemvittata (Queensnake) and Nerodia sipedon (Common Watersnake). We were unable to detect an effect of disease state on short-term survival for either species. However, we estimated Bayesian posterior probabilities of >0.99 that R. septemvittata with SFD spent more time surface-active and were less likely to permanently emigrate from the study area. We also estimated probabilities of 0.98 and 0.87 that temporary immigration and temporary emigration rates, respectively, were lower in diseased R. septemvittata. We found evidence of elevated surface activity and lower temporary immigration rates in diseased N. sipedon, with estimated probabilities of 0.89, and found considerably less support for differences in permanent or temporary emigration rates. This study is the first to yield estimates for key demographic and behavioral parameters (survival, emigration, surface activity) of snakes in wild populations afflicted with SFD. Given the increase in surface activity of diseased snakes, future surveys of snake populations could benefit from exploring longer-term demographic consequences of SFD and recognize that disease prevalence in surface-active animals may exceed that of the population as a whole.

Long‐term survival probability, not current habitat quality, predicts dispersal distance in a stream salamander

Dispersal evolves as an adaptive mechanism to optimize individual fitness across the landscape. Specifically, dispersal represents a mechanism to escape fitness costs resulting from changes in environmental conditions. Decades of empirical work suggest that individuals use local habitat cues to make movement decisions, but theory predicts that dispersal can also evolve as a fixed trait, independent of local conditions, in environments characterized by a history of stochastic spatiotemporal variation. Until now, however, both conditional and fixed models of dispersal evolution have primarily been evaluated using emigration data (stay vs. leave), and not dispersal distances: a more comprehensive measure of dispersal. Our goal was to test whether conditional or fixed models of dispersal evolution predict variation in dispersal distance in the stream salamander Gyrinophilus porphyriticus. We quantified variation in habitat conditions using measures of salamander performance from 4yr of spatially explicit, capture-mark-recapture (CMR) data across three headwater streams in the Hubbard Brook Experimental Forest in central New Hampshire, USA. We used body condition as an index of local habitat quality that individuals may use to make dispersal decisions, and survival probability estimated from multistate CMR models as an index of mortality risk resulting from the long-term history of environmental variation. We found that dispersal distances increased with declining survival probability, indicating that salamanders disperse further in risky environments. Dispersal distances were unrelated to spatial variation in body condition, suggesting that salamanders do not base dispersal distance decisions on local habitat quality. Our study provides the first empirical support for fixed models of dispersal evolution, which predict that dispersal evolves in response to a history of spatiotemporal environmental variation, rather than as a conditional response to current habitat conditions. More broadly, this study underscores the value of assessing alternative scales of environmental variation to gain a more complete and balanced understanding of dispersal evolution.

Demographic and population responses of an apex predator to climate and its prey: a long‐term study of South Polar Skuas

AbstractEcologists widely acknowledge that a complex interplay of endogenous (density‐dependent) and exogenous (density‐independent) factors impact demographic processes. Individuals respond differently to those forces, ultimately shaping the dynamics of wild populations. Most comprehensive studies disentangling simultaneously the effects of density dependence, climate, and prey abundance while taking into account age structure were conducted in terrestrial ecosystems. However, studies on marine populations are lacking. Here we provide insight into the mechanisms affecting four vital rates of an apex Antarctic marine predator population, the South Polar Skua Catharacta maccormicki, by combining a nearly half‐century longitudinal time series of individual life histories and abundance data, with climatic and prey abundance covariates. Using multistate capture–mark–recapture models, we estimated age classes effects on survival, breeding, successful breeding with one or two chicks and successful breeding with two chicks probabilities, and assessed the different effects of population size, climate, and prey abundance on each age‐specific demographic parameter. We found evidence for strong age effects in the four vital rates studied. Vital rates at younger ages were lower than those of older age classes for all parameters. Results clearly evidenced direct and indirect influences of local climate (summer sea ice concentration), of available prey resources (penguins), and of intrinsic factors (size of the breeding population). More covariate effects were found on reproductive rates than on survival, and younger age classes were more sensitive than the older ones. Results from a deterministic age‐structured density‐dependent matrix population model indicated greater effects of prey abundance and sea ice concentration on the total population size than on the breeding population size. Both total population size and the number of breeders were strongly affected by low values of sea ice concentration. Overall, our results highlight the greater sensitivity of reproductive traits and of younger age classes to prey abundance, climate variability, and density dependence in a marine apex predator, with important consequences on the total population size but with limited effects on the breeding population size. We discuss the mechanisms by which climate variability, prey abundance, and population size may affect differentially age‐specific vital rates, and the potential population consequences of future environmental changes.

Winter site use by Afro-Palearctic migrants in Ghana: site persistence and densities of Willow Warbler, Pied Flycatcher, Melodious Warbler and Common Redstart

Little is known about the variation within and among species of long-distance migrants in behavioural strategies and habitat choice on their non-breeding grounds. We report results from regular ringing operations carried out during the winter seasons 2009–2013 and transect counts in 2013, 2015 and 2016 in the Sudan Savanna Zone in Ghana. The best supported capture–mark–recapture model included species-specific probabilities of stay between within-season periods but no differences in resighting probability among species or sites. This model indicated that less than one-third of the Willow Warblers Phylloscopus trochilus and half of the Melodious Warblers Hippolais polyglotta stayed at wintering sites during more than 10 d, whereas for Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus up to 90% stayed for more than 10 d, indicating itinerant wintering behaviour in the warblers and longer non-breeding residency in Pied Flycatcher and Common Redstart. Densities varied among years, but Pied Flycatchers were consistently most numerous in well-matured woodland habitat and Willow Warblers in disturbed habitat. Recaptures among years were too low for meaningful estimates of winter site fidelity, yet recurrence was recorded in three species. We speculate that habitat use is directly related to degree of territory defence and itinerancy.

Evaluating European LIFE conservation projects: Improvements in survival of an endangered vulture

Abstract Long‐lived avian scavengers are threatened worldwide and thus, are common targets of conservation plans. However, scientific evidence of both the factors limiting populations and effectiveness of management actions are greatly needed in order to develop more efficient and successful conservation strategies. We assessed the effectiveness of conservation actions applied within a LIFE‐Nature project aimed at improving the long‐term survival of the critically endangered Canarian Egyptian vulture: including education campaigns for public awareness and control of illegal poisoning and the modification of power lines to reduce the risk of accidents. We formulated a multievent capture–mark–recapture model to obtain estimates of survival for juvenile, subadult and adult birds accounting for probabilities of resight, recovery and losses of metal and colour rings. Models supported a substantial enhancement in survival for subadult and adult birds and a moderate improvement for juveniles after the implementation of LIFE actions. Ring loss probabilities became notably high in the middle to long term. Poisoning events became very rare after LIFE was implemented, suggesting a positive effect of environmental education and awareness campaigns. Entanglements and collisions in power lines were also efficiently mitigated. Instead, electrocutions became the most identified cause of death in the post‐LIFE stage. Synthesis and applications. Our results highlight the improvement of survival in a threatened island vulture population after the implementation of a European LIFE conservation project. On small islands, with small human populations and few stakeholders, education and awareness campaigns can be especially effective for biodiversity conservation. We also demonstrate the need to complement conservation programmes with long‐term monitoring, which is essential to evaluate the effectiveness of actions, especially for long‐lived species.

Combining capture-recapture data and known ages allows estimation of age-dependent survival rates.

In many animal populations, demographic parameters such as survival and recruitment vary markedly with age, as do parameters related to sampling, such as capture probability. Failing to account for such variation can result in biased estimates of population‐level rates. However, estimating age‐dependent survival rates can be challenging because ages of individuals are rarely known unless tagging is done at birth. For many species, it is possible to infer age based on size. In capture–recapture studies of such species, it is possible to use a growth model to infer the age at first capture of individuals. We show how to build estimates of age‐dependent survival into a capture–mark–recapture model based on data obtained in a capture–recapture study. We first show how estimates of age based on length increments closely match those based on definitive aging methods. In simulated analyses, we show that both individual ages and age‐dependent survival rates estimated from simulated data closely match true values. With our approach, we are able to estimate the age‐specific apparent survival rates of Murray and trout cod in the Murray River, Australia. Our model structure provides a flexible framework within which to investigate various aspects of how survival varies with age and will have extensions within a wide range of ecological studies of animals where age can be estimated based on size.