Annual Apparent Survival Rates Research Articles

Use of capture–recapture models to evaluate abundance and dynamics of a stocked Muskellunge population

AbstractTo evaluate the success of a stocking program in Fox Lake, Minnesota, adult (≥76 cm total length) Muskellunge were captured with large nearshore trap nets and individually marked with passive integrated transponder tags during the 2011–2013 and 2015–2017 spawning seasons; then, capture–recapture data were analyzed at two different time scales. Despite substantial sampling effort, daily capture histories within a single season only supported closed‐population abundance estimates for both sexes in half the years; estimates were imprecise, and there was evidence of trap shyness or violation of the short‐term closure assumption in some years. Jolly–Seber models over all years supported relatively precise abundance estimates for both sexes every year, as well as estimates of annual survival, recruitment, and population growth rate. Link–Barker Jolly–Seber models provided estimates of population growth rate λ ≈ 1 indicating that per‐capita annual recruitment rates of only about 0.15–0.20 were adequate to maintain the adult population given the high annual apparent survival rates of 0.80 for adult females and 0.89 for adult males. POPAN Jolly–Seber models revealed that about 80 adult females and 90–126 adult males were vulnerable to capture each year in the 385 ha lake, and about 16–18 fish of each sex recruited to the adult population annually. This study illustrates the importance of open‐population models with multiple years of data to evaluate the abundance and population dynamics of a low‐density, long‐lived species.

Post-release survival of Whiteleg skate (Amblyraja taaf) caught as bycatch on demersal longlines in deep waters of the Southern Ocean (Crozet Archipelago)

Abstract Whiteleg skate (Amblyraja taaf) is a bycatch species commonly discarded in demersal longline fisheries targeting Patagonian toothfish around the Crozet archipelago (Southern Ocean). While there are global conservation issues on elasmobranchs, the post-release survival of this deep-sea species remains unknown. This study is the first tagging programme conducted on Whiteleg skates to investigate their fate after being released at sea. Almost 3000 skates were captured, double-tagged with conventional tags and released between 2020 and 2022 to assess survival using capture–mark–recapture (CMR) models. Our primary result was an estimated annual apparent survival rate higher than 92% for skates released in good condition (with 185 skates recaptured after up to 944 days at liberty). Low detection rate highlighted methodological challenges for CMR models. However, skate size and depth of capture had an effect on apparent survival probability with smaller individuals having lower values (<65 cm; 0.84 ± 0.04) as well as skates caught at shallower depths (<1200 m; 0.83 ± 0.04). Overall, this study suggests that the mandated release of skates in good condition is effective to limit fishing impact on skates in this fishery. To further limit this impact, we recommended changes in fishing practices (hauling speed and soak time).

Survival of red knots in the northern Gulf of Mexico

Highly migratory shorebirds are among the fastest declining avian guilds, so determining causes of mortality is critically important for their conservation. Most of these species depend on a specific geographic arrangement of suitable sites that reliably provide resources needed to fuel physiologically demanding life histories. Long-term mark-resight projects allow researchers to investigate specific potential sources of variation in demographic rates between populations. Red Knots (Calidris canutus) occur in three relatively distinct regions across the northern Gulf of Mexico, and two of these areas have been experiencing episodic harmful algal blooms (red tide) with increased frequency in recent decades. Since knots are mostly molluscivorous during the nonbreeding season in the Gulf, they are potentially exposed to red tide toxins at high concentrations via their filter-feeding prey. We used long-term mark-resight data from Texas, Louisiana, and Florida (USA) to estimate apparent survival, and to assess the effects of red tides on survival of Red Knots. We also assessed effects of tracking devices deployed in conjunction with the projects over the years. While overall apparent annual survival rates were similar across the three locations (0.768 – 0.819), several red tide events were associated with catastrophically low seasonal (fall) survival in Florida (as low as 0.492) and Texas (as low as 0.510). Leg-mounted geolocators, but not temporary glued-on VHF tags, were associated with a reduction in apparent survival (~8%/year). Movement of knots between the three areas was rare and site fidelity is known to be high. Harmful algal blooms are predicted to increase in frequency and severity with climate change and increased anthropogenic degradation of coastal habitats, which may further endanger these as well as other shorebird populations around the world.

Effects of Deforestation on Foraging Behavior, Ectoparasites, and Adult Survival in the Vulnerable La Selle Thrush, Turdus swalesi, in Haiti

Although range-restricted Neotropical bird species are highly endangered, little is known about their ability to cope with environmental disturbance. We studied the vulnerable, Hispaniola- endemic La Selle Thrush (LST), Turdus swalesi, in a protected forested area in Haiti threatened by agriculture, livestock and logging. We used capture–mark–recapture, visual observations, and camera traps to document foraging ecology and estimate adult survival over 26 months. LST foraged mainly in deciduous woodlots. However, some individuals regularly foraged on or around dung pats in fallow pastures, whereas no other ground-dwelling bird species was observed to do so. Coincidently, 16.5% of 79 mist-netted LST harbored Ixodid ticks, compared to none of the 2131 individuals belonging to 29 other species mist-netted in the area. This suggests that infestation with ticks might come as a cost of opportunistically exploiting a new food resource. Apparent annual adult survival rate was independent of sex, and varied between 0.393 and 0.440, depending on the inclusion of a transience effect in our models. This low value was possibly due to “permanent” emigration from the site during the study. We discuss the potential effects of deforestation on the ecology and demography of LST and make recommendations for future conservation-oriented research in Haiti.

Arriving late and lean at a stopover site is selected against in a declining migratory bird population.

Loss and/or deterioration of refuelling habitats have caused population declines in many migratory bird species but whether this results from unequal mortality among individuals varying in migration traits remains to be shown. Based on 13 years of body mass and size data of great knots (Calidris tenuirostris) at a stopover site of the Yellow Sea, combined with resightings of individuals marked at this stopover site along the East Asian-Australasian Flyway, we assessed year to year changes in annual apparent survival rates, and how apparent survival differed between migration phenotypes (i.e. migration timing and fuel stores). The measurements occurred over a period of habitat loss and/or deterioration in this flyway. We found that the annual apparent survival rates of great knots rapidly declined from 2006 to 2018, late-arriving individuals with small fuel stores exhibiting the lowest apparent survival rate. There was an advancement in mean arrival date and an increase in the mean fuel load of stopping birds over the study period. Our results suggest that late-arriving individuals with small fuel loads were selected against. Thus, habitat loss and/or deterioration at staging sites may cause changes in the composition of migratory phenotypes at the population-level.

River- and Sex-Specific Annual Survival Rates of Mature Anadromous Alewife (Alosa pseudoharengus)

During multiple annual spawning runs from 2013 to 2021, over 9,000 mature anadromous alewife (Alosa pseudoharengus A. Wilson, 1811) were monitored with passive integrated transponders (PITs) in four rivers of the Chignecto Isthmus, Bay of Fundy, Canada. A subsample of 384 individuals tagged during 2016–2019 were aged from 3 to 6 years (mean ± SD; 4.2 ± 0.7 years, n = 232, males; 4.5 ± 0.7 years, n = 152, females). Biotelemetry revealed that one unsexed individual survived seven years post tagging, possibly making it 10–13 years old. Return rates varied among the rivers, with the lowest rates in the most anthropogenically impacted river. Biotelemetry and ageing data were used to estimate apparent annual survival rates ranging from 0.25 to 0.50 depending on the river and the year. Based on capture-mark-recapture (CMR) analysis of biotelemetry data from the three less impacted rivers, the estimated overall annual survival was 0.396, total instantaneous mortality (Z) was 0.93, and future life expectancy from time of release was 1.08 years. Frequency distribution of ages 4–6 for alewife pooled from all four study rivers estimated a lower annual survival rate of 0.301, Z = 1.20, and a future life expectancy of 0.83 years. The biotelemetry detection rates were 0.89–0.98 but varied depending on the river and the year, with the lowest rates in one river during 2017-2018 possibly related to a malfunctioning tide gate preventing upstream fish passage and subsequent detection. Based on CMR, males had a higher survival rate compared to females, which translated into an overall mean survival increase of 0.05. Alewife survivorship in our study highlighted that a limited ecosystem-based management period is required to mitigate river connectivity and mortality issues to avoid loss of population cohorts and decrease the risk of extirpation.

Annual adult survival rates for four sympatric breeding swallow species: effects of environmental factors and density-dependence

Swallow (Family: Hirundinidae) populations in the Canadian Maritimes have declined since the 1980s. Using mark–recapture data from 2012 to 2019, we determined apparent annual adult survival rates for Barn ( Hirundo rustica Linnaeus, 1758), Tree ( Tachycineta bicolor (Vieillot, 1808)), Bank ( Riparia riparia (Linnaeus, 1758)), and Cliff ( Petrochelidon pyrrhonota (Vieillot, 1817)) swallows. For two data-rich species (Barn and Tree swallows), we modelled the relationships between survival and weather (cold snaps, precipitation, temperature, and wind speed), climate (El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO)), Enhanced Vegetation Index (EVI) as a measure of primary productivity during the winter, number of active nests as a measure of site quality, and the Breeding Bird Survey (BBS) annual population index as density-dependent processes. Survival rates for all four species were typically higher (Barn and Tree) or similar to (Cliff and Bank) of estimates from populations that have not undergone severe, long-term declines. Across weather and climate variables, conditions that are typically favourable for high insect availability (e.g., higher precipitation, warmer temperatures, and lower wind speeds) resulted in higher survival. For female Barn and Tree swallows, survival was higher when EVI was lower, and for Barn Swallows, survival was also higher when the BBS index was higher. Collectively our results demonstrate that conditions throughout the annual cycle affect survival, and the relationships with weather and climate variables support the importance of high insect availability.

Implications of non-ideal occupancy for the measurement of territory quality

Territory quality shapes population dynamics and has conservation implications for territorial species. Yet, quantifying territory quality using different measures can yield conflicting results, particularly if territory selection is non-ideal, thus challenging the understanding of territory quality. We used a 25-year population study of spotted owls ( Strix occidentalis ) occupying 72 territories to evaluate five commonly used demographic- and occupancy-based measures of territory quality: occupancy rate, annual apparent survival rate, territory fitness, mean annual reproductive rate, and total reproductive output. To do so, we evaluated pairwise relationships between measures of territory quality and assessed the extent to which spotted owls selected territories based on their potential to promote fitness. Measures of territory quality were generally positively correlated. Notably, however, territory occupancy explained less than half of the variation (R 2 = 0.37) in territory fitness (the expected fitness of territory holders). Non-ideal patterns in territory occupancy were the result of weak linkages between the likelihood of vacant territories becoming colonized and their fitness potential, particularly their capacity to promote reproduction. Imperfect territory colonization was likely the product of the spotted owl’s strong site fidelity to even low-fitness territories and constraints on the ability of dispersing individuals to locate high quality territories. Mismatches emerging from non-ideal colonization have important conservation implications because populations may benefit more from habitat restoration at low fitness-high occupancy territories and more from conspecific attraction measures at high fitness-low occupancy territories. Our findings for spotted owls were reasonably consistent with broad patterns observed for other species in previous studies, but the strength of associations between pairs of territory quality measures often varied considerably, suggesting that species-specific assessments of patterns in territory quality are important. Finally, when practical, examination of the ecological processes shaping multiple measures of territory quality will benefit the study and conservation of territorial species.

Evaluation of ongoing Crested Ibis (Nipponia nippon) reintroduction using an integrated population model and Bayesian population viability analysis

Reintroduction has often been used as a technique for re‐establishing self‐sustaining animal populations that have become extinct within their indigenous range. To achieve conservation success, it is essential to accurately assess the demographic parameters and the IUCN Red List criteria of the population. However, acquiring data on all indicators and estimating criteria according to established definitions can be challenging. Here, we developed an integrated population model (IPM) and population viability analysis (PVA) framework to estimate all demographic parameters and criteria for a reintroduced population of Crested IbisNipponia nippon, and to project population dynamics under a range of release scenarios on Sado Island, Japan. Our IPM‐PVA framework integrated roost count and mark–resight data for 415 released and 203 wild‐hatched individuals, as well as reproductive performance for a total of 575 pairs. We aimed to assess survival, reproductive success, population size, number of mature individuals and population projection. In the first year after release, the estimated apparent annual survival rate was 0.566 [Bayesian credible intervals (CRI) 0.518–0.614]; however, this rate increased after 1 year (0.865; CRI 0.836–0.892). Wild‐hatched juveniles exhibited a high survival rate (0.757; CRI 0.670–0.838) that was just lower than that of adults (0.899; CRI 0.844–0.949). The reproductive success rate varied with pair attributes (released–released pair: 0.245, CRI 0.194–0.299; released–wild pair: 0.377, CRI 0.281–0.471; wild–wild pair: 0.350, CRI 0.237–0.471). Total population size was estimated to be 457 individuals (CRI 384–525), with 261 mature individuals (CRI 211–304) in June 2021. The probability of Crested Ibis extinction in the next five generations was 0%, even if the release was discontinued. Our comprehensive case study demonstrated the effectiveness of IPM‐PVA for the evaluation of ongoing reintroduction programmes.

High long‐term survival and asymmetric movements in a reintroduced metapopulation of Cinereous vultures

AbstractPost‐release mortality and movements are critical factors of translocation failure. Yet, survival and movement reflect different demographic and behavioral processes and may therefore have contrasted responses to management, although they are often very difficult to disentangle in animal populations. To provide guidance in animal translocations, we discriminated the respective roles of survival and movement in the long‐term dynamic of a translocated metapopulation of Cinereous vultures (Aegypius monachus) in France using multievent capture–recapture analyses of reintroduced (n = 119) and wild‐born individual (n = 163) observations. Annual apparent survival rates were high and structured in age (>0.8 for young and >0.9 for adults) and did not differ between individual origin (wild‐born or released), release methods (aviary or hacking) nor between regions (Alps and Causses), except for those released in the Alps experiencing a reduced survival for one year after release. In contrast, age structure movements differed between populations and origin status. Wild‐born young from the Causses were more erratic than those from the Alps and older individuals, whereas vultures reintroduced in the Causses demonstrated restricted movements during their first year after release. Despite such asymmetric movements, we overall highlight a strong tropism of individuals whatever the region and their origin. Since movement and survival were respectively higher and lower in young compared with adults, we recommend to first release adults in the primary stage of metapopulation translocations for increasing the establishment success at the release site. Further releasing young and securing successful breeding into the wild would increase demographic growth and between‐population connections.

Using Acoustic Telemetry to Estimate Weakfish Survival Rates along the U.S. East Coast

AbstractThe Weakfish Cynoscion regalis, an economically important species, has declined over the last 30 years, corresponding with an increase in total mortality according to the most recent stock assessment. We estimated estuarine‐specific and coastwide apparent survival of Weakfish by using a Cormack–Jolly–Seber model to provide insights into the spatiotemporal component of mortality. Telemetered Weakfish (n = 342) were released across five estuaries ranging from North Carolina to New Jersey between 2006 and 2016. In estuaries from Delaware Bay and northward, egress peaked around the third week of September; in North Carolina, egress peaked by the first week of November. For three estuaries with adequate sample sizes, apparent survival estimates were similar and a joint model including all telemetered Weakfish estimated an extremely low annual apparent survival rate of 0.001 (95% credible interval [CrI] = 0.002–0.0003) or annual apparent instantaneous total mortality of 7.25 (95% CrI = 6.28–8.05). At a minimum, 61% of telemetered Weakfish emigrated in the fall, but only 2 of 149 fish with long‐lived transmitters were detected as returning to estuaries the following year. This is a small proportion for a fish that exhibits spawning site fidelity. We conclude that the disappearance of telemetered Weakfish represents mortality that occurs between emigration and the spring spawning period, potentially during overwinter periods on the continental shelf. Our study provides insights into the magnitude, timing, and location of Weakfish loss and facilitates an improved understanding of Weakfish population dynamics for use in stock rebuilding.

Abundance and site fidelity of bottlenose dolphins off a remote oceanic island (Reunion Island, southwest Indian Ocean)

AbstractThis study represents the first comprehensive assessment of the population dynamics and residency of common bottlenose dolphin around Reunion Island (southwest Indian Ocean). Understanding dynamics and movement patterns of this local population is essential to guide effective conservation efforts, notably in a context of growing dolphin‐watching activities. Dedicated surveys based on photo‐identification methods were conducted over 6 years (2010–2015). The species was present year‐round, in groups of 25 individuals on average (1–150). Jolly‐Seber mark‐recapture models resulted in a population estimate of 254 individuals (95% CI = 191–337) and an apparent annual survival rate of 0.83. The population was almost equally split into three residency patterns: residents (33.1%), long‐term visitors (32.6%), and short‐term visitors (34.3%, including transients, i.e., individuals only seen once [14.9%]), suggesting that the majority of the population showed a moderate‐to‐high level of residency in the study area. Individuals from the three residency patterns associated randomly, mixing together and forming a single community. Models based on the lagged identification rate indicated emigration and reimmigration to the survey area, with some individuals occupying the study area for about 2 years (832 days), and remaining outside for an average of 276 days, probably exhibiting larger home ranges and extensive movement behavior.

Variation of annual apparent survival and detection rates with age, year and individual identity in male Weddell seals (Leptonychotes weddellii) from long‐term mark‐recapture data

AbstractExploring age‐ and sex‐specific survival rates provides insight regarding population behavior and life‐history trait evolution. However, our understanding of how age‐specific patterns of survival, including actuarial senescence, compare between the sexes remains inadequate. Using 36 years of mark‐recapture data for 7,516 male Weddell seals (Leptonychotes weddellii) born in Erebus Bay, Antarctica, we estimated age‐specific annual survival rates using a hierarchical model for mark‐recapture data in a Bayesian framework. Our male survival estimates were moderate for pups and yearlings, highest for 2‐year‐olds, and gradually declined with age thereafter such that the oldest animals observed had the lowest rates of any age. Reports of senescence in other wildlife populations of species with similar longevity occurred at older ages than those presented here. When compared to recently published estimates for reproductive Weddell seal females, we found that peak survival rates were similar (males: 0.94, 95% CI = 0.92–0.96; females: 0.92, 95% CI = 0.93–0.95), but survival rates at older ages were lower in males. Age‐specific male Weddell seal survival rates varied across years and individuals, with greater variation occurring across years. Similar studies on a broad range of species are needed to contextualize these results for a better understanding of the variation in senescence patterns between the sexes of the same species, but our study adds information for a marine mammal species to a research topic dominated by avian and ungulate species.

Estimating correlations among demographic parameters in population models.

Estimating correlations among demographic parameters is critical to understanding population dynamics and life‐history evolution, where correlations among parameters can inform our understanding of life‐history trade‐offs, result in effective applied conservation actions, and shed light on evolutionary ecology. The most common approaches rely on the multivariate normal distribution, and its conjugate inverse Wishart prior distribution. However, the inverse Wishart prior for the covariance matrix of multivariate normal distributions has a strong influence on posterior distributions. As an alternative to the inverse Wishart distribution, we individually parameterize the covariance matrix of a multivariate normal distribution to accurately estimate variances (σ 2) of, and process correlations (ρ) between, demographic parameters. We evaluate this approach using simulated capture–mark–recapture data. We then use this method to examine process correlations between adult and juvenile survival of black brent geese marked on the Yukon–Kuskokwim River Delta, Alaska (1988–2014). Our parameterization consistently outperformed the conjugate inverse Wishart prior for simulated data, where the means of posterior distributions estimated using an inverse Wishart prior were substantially different from the values used to simulate the data. Brent adult and juvenile annual apparent survival rates were strongly positively correlated (ρ = 0.563, 95% CRI 0.181–0.823), suggesting that habitat conditions have significant effects on both adult and juvenile survival. We provide robust simulation tools, and our methods can readily be expanded for use in other capture–recapture or capture‐recovery frameworks. Further, our work reveals limits on the utility of these approaches when study duration or sample sizes are small.

Demography and welfare status of free-roaming dogs in Yangmingshan National Park, Taiwan

Free-roaming dogs (Canis familiaris) cause threats to native wildlife and public health and raise concerns for their welfare. Understanding the demography of free-roaming dog populations is essential for developing an effective management plan. An evaluation of their welfare status would be beneficial to earn public support for the management plan. In this study, we estimated the population size, survivorship, and health of a free-roaming dog population in Yangmingshan National Park (YMSNP), Taiwan, during 2016–2018. YMSNP is a rural area with human settlements but also a protected area of conservation concern. We identified 191, 176, 216 individuals at our sampling sites in 2016, 2017, and 2018, respectively. Using a photographic capture-recapture method and extrapolation, we estimated that there were 786–979 dogs in the park during this 3-year period. The annual apparent survival rate of identified dogs was 16.7% for 2016–2017 and 23.9% for 2017–2018. The dogs had a high rate of lameness and dermatosis of 5.1–8.8% and 14.2–18.1%, respectively. Thirty-five blood samples showed that 34.3% of the dogs were anemic, 37.1% showed abnormal white blood cell counts, and 68.6% exhibited abnormal platelet counts. These results suggested that the dogs were at high density with low survivorship and in poor health, and new individuals entered the population continuously. Interventions to manage this dog population and to improve their welfare must be carried out. Our study provides an example for monitoring and managing a free-roaming dog population in a rural, conservation area in Southeast Asia.

Size-specific apparent survival rate estimates of white sharks using mark–recapture models

For species that exist at low abundance or are otherwise difficult to study, it is challenging to estimate vital rates such as survival and fecundity and common to assume that survival rates are constant across ages and sexes. Population assessments based on overly simplistic vital rates can lead to erroneous conclusions. We estimated sex- and length-based annual apparent survival rates for white sharks (Carcharodon carcharias). We found evidence that annual apparent survival differed over ontogeny in a system with competitive foraging aggregations, from 0.63 (standard error (SE) = 0.08) for newly recruiting subadults to 0.95 (SE = 0.02) for the largest sharks. Our results reveal a potential challenge to ontogenetic recruitment in a long-lived, highly mobile top marine predator, as survival rates for subadult white sharks may be lower than previously assumed. Alternatively, younger and competitively inferior individuals may be forced to permanently emigrate from primary foraging sites. This study provides new methodology for estimating apparent survival as a function of diverse covariates by capture–recapture study, including when sex assignment is uncertain.

Sensitivity Analysis Using Site-Specific Demographic Parameters to Guide Research and Management of Threatened Eastern Massasaugas

Long-term demographic data are important for conserving populations of threatened and endangered species. Collecting data specific to the population of interest can improve conservation success by allowing managers to make informed decisions, evaluate the efficacy of habitat management, and assess extinction risk. Population viability analysis (PVA), a tool commonly used to estimate extinction risk in threatened populations, is most informative when precise, population-specific data are available. We used mark-recapture data spanning ten years (2008–2017) to estimate annual adult survival rates in a population of threatened Eastern Massasauga rattlesnakes (Sistrurus catenatus) in Barry County, Michigan. Using these survival estimates and ten additional parameter values obtained from our site and a nearby population, we modeled population viability over the next 100 years. We performed sensitivity analysis using Latin hypercube sampling, followed by logistic regression to assess the relative influence of model parameters on extinction risk. We estimated annual apparent survival rates of 0.79 (95% CI = 0.69–0.87) for adult males and 0.78 (95% CI = 0.69–0.85) for adult females, which are higher than expected given the population's locality. Results of our sensitivity analysis suggest that actions promoting high survival of adult females should be a management priority, followed by activities that facilitate high reproductive output and neonate survival. We recommend focusing future research and monitoring efforts on these parameters.

Estimating population extinction thresholds with categorical classification trees for Louisiana black bears.

Monitoring vulnerable species is critical for their conservation. Thresholds or tipping points are commonly used to indicate when populations become vulnerable to extinction and to trigger changes in conservation actions. However, quantitative methods to determine such thresholds have not been well explored. The Louisiana black bear (Ursus americanus luteolus) was removed from the list of threatened and endangered species under the U.S. Endangered Species Act in 2016 and our objectives were to determine the most appropriate parameters and thresholds for monitoring and management action. Capture mark recapture (CMR) data from 2006 to 2012 were used to estimate population parameters and variances. We used stochastic population simulations and conditional classification trees to identify demographic rates for monitoring that would be most indicative of heighted extinction risk. We then identified thresholds that would be reliable predictors of population viability. Conditional classification trees indicated that annual apparent survival rates for adult females averaged over 5 years () was the best predictor of population persistence. Specifically, population persistence was estimated to be ≥95% over 100 years when , suggesting that this statistic can be used as threshold to trigger management intervention. Our evaluation produced monitoring protocols that reliably predicted population persistence and was cost-effective. We conclude that population projections and conditional classification trees can be valuable tools for identifying extinction thresholds used in monitoring programs.

Demographic data on the Little Owl(Athene noctua)in Upper-Kiskunság (Hungary)

AbstractThis study focused on the clutch size and age-specific apparent survival rate of the Little Owl(Athene noctua)population in Upper-Kiskunság, Hungary. Between May 2005 and April 2017, 640 individuals were captured and ringed in a total of 746 capture-recapture occasions. Artificial nest boxes were installed in the study area, breeding birds and pulli were captured for ringing/recaptured in these boxes (from March to May), or at the close neighbourhood of those (max. 168 m). Jolly-Seber’s open population method was applied to model the survival rate. The candidate model set included models incorporating age, year-effect, and the combination of those. AICc value was used to compare models in a selection approach. The final model was constructed via model averaging based on the models with significant explanatory power. The average number and SD of pullus/breeding pair was 3.78 ± 0.76. The average apparent annual survival rate (which does not differentiate between mortality and permanent emigration) for the period between pullus stage and the time of the first breeding was estimated as 9.47% ± 2.99% SE, whereas the annual survival rate of adults was 82.74% ± 8.46% SE. The effect of sex on the survival rate of adults was not investigated due to female-biased sample, as the probability of capturing females is significantly higher in late spring months. Our experience reveals that during February and March it is possible to capture both sexes in the nest boxes, and it does not influence negatively the breeding success. Based on our results, the population of the Little Owl is stable in Upper-Kiskunság. A slight increase in estimated population size is observable even if we make no difference between mortality and permanent emigration. The high occupancy rate of the installed nest boxes reveals that nest site availability is an important limiting factor in the studied population.

Tidal Habitats Support Large Numbers of Invasive Blue Catfish in a Chesapeake Bay Subestuary

The introduction of a non-native freshwater fish, blue catfish Ictalurus furcatus, in tributaries of Chesapeake Bay resulted in the establishment of fisheries and in the expansion of the population into brackish habitats. Blue catfish are an invasive species in the Chesapeake Bay region, and efforts are underway to limit their impacts on native communities. Key characteristics of the population (population size, survival rates) are unknown, but such knowledge is useful in understanding the impact of blue catfish in estuarine systems. We estimated population size and survival rates of blue catfish in tidal habitats of the James River subestuary. We tagged 34,252 blue catfish during July–August 2012 and 2013; information from live recaptures (n = 1177) and dead recoveries (n = 279) were used to estimate annual survival rates and population size using Barker’s Model in a Robust Design and allowing for heterogeneity in detection probabilities. The blue catfish population in the 12-km study area was estimated to be 1.6 million fish in 2013 (95% confidence interval [CI] adjusted for overdispersion: 926,307–2,914,208 fish). Annual apparent survival rate estimates were low: 0.16 (95% CI 0.10–0.24) in 2012–2013 and 0.44 (95% CI 0.31–0.58) in 2013–2014 and represent losses from the population through mortality, permanent emigration, or both. The tagged fish included individuals that were large enough to exhibit piscivory and represented size classes that are likely to colonize estuarine habitats. The large population size that we estimated was unexpected for a freshwater fish in tidal habitats and highlights the need to effectively manage such species.