Geographic variation and environmental correlates of apparent survival rates in adult tree swallows Tachycineta bicolor

Determining demographic rates in wild animal populations and understanding why rates vary are important challenges in population ecology and conservation. Whereas reproductive success is reported frequently for many songbird species, there are relatively few corresponding estimates of annual survival for widespread populations of the same migratory species. We incorporated mark–recapture data into Cormack–Jolly–Seber models to estimate annual apparent survival and recapture rates of adult male and female tree swallows Tachycineta bicolor in eight local breeding populations across North America for periods of 7–33 yr. We found strong site‐specific and annual variation in apparent survival rates of adult swallows, and evidence of higher survival or site fidelity among males than females. There were no strong associations between putative overwintering region and survival. Strength and patterns of winter climate‐apparent survival relationships varied across four sites monitored for >15 yr; at one site, spring pond conditions, local spring precipitation and, to a lesser extent, winter North Atlantic Oscillation Index were credible predictors of annual apparent survival. Further work is needed to evaluate how survival is related to environmental conditions throughout the annual cycle and how these factors affect population dynamics of swallows and related species of conservation concern.     

Modelling the effect of fishing on southern Buller's albatross using a 60-year dataset

Abstract

Many albatross populations are declining and a major cause is believed to be incidental mortality from fishing. We investigated the effect of fishing on southern Buller's albatross Thalassarche bulleri bulleri, using a new approach to seabird population modelling that allows estimation of demographic parameters from multiple data types. Three types of data were used: a 60-year set of mark–recapture observations, four censuses of the breeding population, and estimates of fishing effort and bycatch. The fisheries risk to the viability of this population over the last 60 years appears to have been small, since the adult population is estimated to have increased about five-fold over that time. There is some cause for concern in recent changes (population growth has slowed, and perhaps reversed, and adult survival rates are falling). The most common age at first breeding was 12 years, and about 80% of adults breed each year. Annual survival was estimated to be 0.91 for juveniles, and varied between this value and 1 for adults. Though this population is not in immediate danger from fishing, there is a need for continued monitoring to see whether the recent fall in survival rates persists and causes a decline in abundance. Our analysis showed that when, as is common, mark–recapture data do not provide good estimates of all demographic rates, the assessment of seabird population trends can be improved by the use of other types of data, particularly abundance.     

Information transfer about roosts in female Bechstein's bats: an experimental field study

Information transfer among group members is believed to play an important part in the evolution of coloniality in both birds and bats. Although information transfer has received much scientific interest, field studies using experiments to test the underlying hypotheses are rare. We used a field experiment to test if communally breeding female Bechstein's bats (Myotis bechsteinii) exchange information regarding novel roosts. We supplied a wild colony, comprising 17 adult females of known relatedness, with pairs of suitable and unsuitable roosts and monitored the arrival of individuals marked with transponders (PIT-tags) over 2 years. As expected with information transfer, significantly more naive females were recruited towards suitable than towards unsuitable roosts. We conclude that information transfer about roosts has two functions: (i) it generates communal knowledge of a large set of roosts; and (ii) it aids avoidance of colony fission during roost switching. Both functions seem important in Bechstein's bats, in which colonies depend on many day roosts and where colony members live together for many years.     

Experimental harvest regulations reveal that water availability during spring,not harvest,affects change in a waterfowl population

Population change is regulated by vital rates that are influenced by environmental conditions, demographic stochasticity, and, increasingly, anthropogenic effects. Habitat destruction and climate change threaten the future of many wildlife populations, and there are additional concerns regarding the effects of harvest rates on demographic components of harvested organisms. Further, many population managers strictly manage harvest of wild organisms to mediate population trends of these populations. The goal of our study was to decouple harvest and environmental variability in a closely monitored population of wild ducks in North America, where we experimentally regulated harvest independently of environmental variation over a period of 4 years. We used 9 years of capture–mark–recapture data to estimate breeding population size during the spring for a population of wood ducks in Nevada. We then assessed the effect of one environmental variable and harvest pressure on annual changes in the breeding population size. Climatic conditions influencing water availability were strongly positively related to population growth rates of wood ducks in our study system. In contrast, harvest regulations and harvest rates did not affect population growth rates. We suggest efforts to conserve waterfowl should focus on the effects of habitat loss in breeding areas and climate change, which will likely affect precipitation regimes in the future. We demonstrate the utility of capture–mark–recapture methods to estimate abundance of species which are difficult to survey and test the impacts of anthropogenic harvest and climate on populations. Finally, our results continue to add to the importance of experimentation in applied conservation biology, where we believe that continued experiments on nonthreatened species will be critically important as researchers attempt to understand how to quantify and mitigate direct anthropogenic impacts in a changing world.     

On the sustainability of a reintroduced Crested Ibis population in Qinling Mountains,Shaanxi, Central China

Reintroduction projects aim to reestablish a self‐sustaining population of an endangered species within its historical range. Adequate post‐release monitoring by gathering demographic data is important to evaluate the success of a reintroduction. Survival and reproduction rates of a reintroduced population can be compared with a self‐sustaining wild population to evaluate the success of a reintroduction. In early 2007, Nipponia nippon (Crested Ibis) was reintroduced into the Qinling Mountains (Shaanxi, Central China). In this study, we attempt to evaluate the demographic status of the reintroduced population. Age‐specific survival rates of 56 released adults and 77 wild‐born fledglings were estimated using mark‐recapture data obtained from 2007 to 2014. Survival rates for the yearlings (0.599, with 95% confidence interval [CI]: 0.467–0.719) were lower than the estimates from a wild population in Yangxian County, but the survival rates of the adults (0.678, with 95% CI: 0.603–0.745) were similar. The number of breeding pairs gradually increased since 2008, although breeding success (52.5%) was somewhat less than that of the wild population (67.6%). The stochastic estimation of population growth rate (1.084 with 95% CI: 1.069–1.098) and population size (5‐fold increase) estimated from an age‐classified Leslie matrix indicate that the reintroduced population of the Crested Ibis is more likely in regulation phase over the next 25 years. We conclude that the reintroduction of the Crested Ibis in Qinling Mountains has great promise, and progress toward a self‐sustaining population has been made under some interventions. Governments, local communities, and scientists need to facilitate habitat restoration for the long‐term survival of this endangered species.     

Estimating demographics of the Nile crocodile (Crocodylus niloticus Laurenti) in the panhandle region of the Okavango Delta,Botswana

The population status of the Nile crocodile (Crocodylus niloticus Laurenti) in the panhandle region of the Okavango Delta, Botswana, was assessed using mark–recapture and spotlight survey techniques following a decline because of commercial utilization. A total of 1717 individuals, ranging from 136 to 2780 mm in Snout Vent Length, were captured over a 4‐year period. Eighty‐one per cent of young juveniles encountered were successfully captured, representing 59.3% of total captures and 75% of recaptures. A Bayesian technique was used to estimate the number of young juveniles, and these estimates were then extrapolated for the other size classes. Survival and recapture analyses highlighted individual size‐dependent increases in wariness and survival. The total annual population was estimated to be 2570 ± 151.06 individuals, with an adult population of 649.2 individuals, including 364 females. We suggest that the harvest of breeding animals for commercial purposes should be halted until population recovery in this region is established.     

Day roost selection in female Bechstein's bats (Myotis bechsteinii): a field experiment to determine the influence of roost temperature

The decision where to live has far-reaching fitness consequences for animals. In contrast to most other mammals or birds that use sheltered nest sites, female Bechstein's bats frequently switch day roosts during one breeding season, and therefore must often decide where to spend the day. Selecting the right roost is important, because roost quality, e.g. microclimatic condition, influences survival and reproduction in bats. Although thermal factors are very important for the quality of roosts occupied by bats, whether bats base their day roost selection directly on roost temperature has not been tested in the field. Over one summer, we examined and tested the roost choice of 21 individually marked female Myotis bechsteinii living in one maternity colony. In a field experiment, we allowed the bats to choose between relatively warm versus cold bat boxes, while controlling for site preferences. We expected females to exhibit a preference for warm roosts during pregnancy and lactation to accelerate gestation and shorten the period of growth of their young. Roost occupancy over 160 census days reflected significant temperature differences among 89 surveyed roosts (14 tree holes and 75 bat boxes), and preferences changed with the season. Females significantly preferred cold roosts before parturition, whereas post-partum, they significantly favoured warm roosts. Temperature preferences were independent of the roost site, and thus roost selection was based directly on temperature. Boxes with significantly different daytime temperatures did not differ significantly at night. Consequently, bats would have to spend at least 1 day in a new roost to test it. Information transfer among colony members might facilitate knowledge of roost availability. Access to many roosts providing different microclimates is likely to be important for successful reproduction in the endangered Bechstein's bat.     

Population dynamics of little brown bats (Myotis lucifugus) at summer roosts: Apparent survival,fidelity, abundance,and the influence of winter conditions

1. White‐nose syndrome (WNS) has caused the death of millions of bats, but the impacts have been more difficult to identify in western North America. Understanding how WNS, or other threats, impacts western bats may require monitoring other roosts, such as maternity roosts and night roosts, where bats aggregate in large numbers.
2. Little brown bats (Myotis lucifugus) are experiencing some of the greatest declines from WNS. Estimating survival and understanding population dynamics can provide valuable data for assessing population declines and informing conservation efforts.
3. We conducted a 5‐year mark–recapture study of two M. lucifugus roosts in Colorado. We used the robust design model to estimate apparent survival, fidelity, and abundance to understand population dynamics, and environmental covariates to understand how summer and winter weather conditions impact adult female survival. We compared the fidelity and capture probability of M. lucifugus between colonies to understand how bats use such roosts.
4. Overwinter survival increased with the number of days with temperatures below freezing (β > 0.100, SE = 0.003) and decreased with the number of days with snow cover (β < −0.40, SE < 0.13). Adult female fidelity was higher at one maternity roost than the other. Overwinter and oversummer adult female survival was high (>0.90), and based on survival estimates and fungal‐swabbing results, we believe these populations have yet to experience WNS.
5. Recapture of M. lucifugus using antennas that continuously read passive integrated transponder tags allows rigorous estimation of bat population parameters that can elucidate trends in abundance and changes in survival. Monitoring populations at summer roosts can provide unique population ecology data that monitoring hibernacula alone may not. Because few adult males are captured at maternity colonies, and juvenile males have low fidelity, additional effort should focus on understanding male M. lucifugus population dynamics.

     

A population study of bats of the Genus Plecotus

In November 1960, bat colonies were found in the roof of the research station, and an ecological study began of the largest, a Plecotus colony. That colony was at first thought to consist solely of P. auritus but, in 1964, the presence of P. austriacus was confirmed, and several of the latter had been ringed early in 1961. Because of this, it has been necessary to present, here, the combined results for the two species. Population studies revealed that the colony size was constant and consisted of 36 bats of which 23 were females. Overall 38% were males but, of the juveniles, 46% were males. The survival rate for the colony as a whole was 0.750, but the mean life expectation for females was 4.2 years and for males 3.7 years. The life-span was thought to be in excess of 16 years. Initial capture rate of 0.715 remained constant throughout the five-year period, while the recapture rate fell by a factor of 0.30. This was attributed to sampling disturbance and not due to ringing. Mating was found to occur equally in spring and autumn. Males became mature in their first year and females in their second. The mean spring and autumn weights for mature males were generally 1.5g less than the corresponding mature female weights, and juvenilesare approximately 1.0 g less than these. Climatic effects on the bats were demonstrated with particular reference to wind velocity. This work is beingcontinued.     

An integrated population model for a long‐lived ungulate: more efficient data use with Bayesian methods

We develop an integrated population model for Svalbard reindeer Rangifer tarandus platyrhynchus, and demonstrate how this type of model can be used to extract more information from the data and separate different sources of variability in population estimates. Our model combines individual mark–recapture data with population counts and harvesting data within a Bayesian model framework, and accounts for observation error, environmental and demographic stochasticity, and age structure. From this model we obtain annual estimates of age‐specific population size, survival and fecundity. The model provides estimates of age structure at a finer scale than that found in the census data, and enables us to estimate survival for the period before calves are first caught and marked, i.e. before they enter the individual mark–recapture data. The modeling framework provides an improved approach to studying age‐structured populations that are imperfectly censused and where the demography of only a sample of individuals is known. We use data from independent censuses of the same population to evaluate population estimates obtained from the model, and show that it is successful at correcting for different types of observation error. Based on our model results, we suggest that allocating resources to the collection of supplementary mark–recapture data could improve the reliability of population projections more than making regular population censuses as exhaustive as possible. Our work demonstrates how integrated Bayesian population modeling can be used to increase the amount of information extracted from collections of data, identifying and disentangling sources of variation in individual performance and population size. This represents an important step towards increasing the predictive ability of population growth models for long‐lived species experiencing changes in environmental conditions and harvesting regimes.     

Climate change and annual survival in a temperate passerine: partitioning seasonal effects and predicting future patterns

Predicting climate change impacts on population size requires detailed understanding of how climate influences key demographic rates, such as survival. This knowledge is frequently unavailable, even in well‐studied taxa such as birds. In temperate regions, most research into climatic effects on annual survival in resident passerines has focussed on winter temperature. Few studies have investigated potential precipitation effects and most assume little impact of breeding season weather. We use a 19‐year capture–mark–recapture study to provide a rare empirical analysis of how variation in temperature and precipitation throughout the entire year influences adult annual survival in a temperate passerine, the long‐tailed tit Aegithalos caudatus. We use model averaging to predict longer‐term historical survival rates, and future survival until the year 2100. Our model explains 73% of the interannual variation in survival rates. In contrast to current theory, we find a strong precipitation effect and no effect of variation in winter weather on adult annual survival, which is correlated most strongly to breeding season (spring) weather. Warm springs and autumns increase annual survival, but wet springs reduce survival and alter the form of the relationship between spring temperature and annual survival. There is little evidence for density dependence across the observed variation in population size. Using our model to estimate historical survival rates indicates that recent spring warming has led to an upward trend in survival rates, which has probably contributed to the observed long‐term increase in the UK long‐tailed tit population. Future climate change is predicted to further increase survival, under a broad range of carbon emissions scenarios and probabilistic climate change outcomes, even if precipitation increases substantially. We demonstrate the importance of considering weather over the entire annual cycle, and of considering precipitation and temperature in combination, in order to develop robust predictive models of demographic responses to climate change. Synthesis Prediction of climate change impacts demands understanding of how climate influences key demographic rates. In our 19‐year mark‐recapture study of long‐tailed tits Aegithalos caudatus, weather explained 73% of the inter‐annual variation in adult survival; warm springs and autumns increased survival, wet springs reduced survival, but winter weather had little effect. Robust predictions thus require consideration of the entire annual cycle and should not focus solely on temperature. Unexpectedly, survival appeared not to be strongly density‐dependent, so we use historical climate data to infer that recent climate change has enhanced survival over the four decades in which the UK long‐tailed tit population has more than doubled. Furthermore, survival rates in this species are predicted to further increase under a wide range of future climate scenarios.     

Apparent survival and return rate of breeders in the southern temperate White‐rumped Swallow Tachycineta leucorrhoa

Life‐histories and demographic parameters of southern temperate bird species have been little studied. We estimated return rates between years and sexes, and adult apparent survival and recapture probabilities with mark–recapture data on White‐rumped Swallows and found a lower return rate of unsuccessful females. There was little support for influences of sex or year on survival rates. The estimates were equivalent to the lowest value reported for a northern congener, in contrast to the prediction of geographical variation under life‐history theory.     

Inferences about population dynamics from count data using multistate models: a comparison to capture–recapture approaches

Wildlife populations consist of individuals that contribute disproportionately to growth and viability. Understanding a population's spatial and temporal dynamics requires estimates of abundance and demographic rates that account for this heterogeneity. Estimating these quantities can be difficult, requiring years of intensive data collection. Often, this is accomplished through the capture and recapture of individual animals, which is generally only feasible at a limited number of locations. In contrast, N‐mixture models allow for the estimation of abundance, and spatial variation in abundance, from count data alone. We extend recently developed multistate, open population N‐mixture models, which can additionally estimate demographic rates based on an organism's life history characteristics. In our extension, we develop an approach to account for the case where not all individuals can be assigned to a state during sampling. Using only state‐specific count data, we show how our model can be used to estimate local population abundance, as well as density‐dependent recruitment rates and state‐specific survival. We apply our model to a population of black‐throated blue warblers (Setophaga caerulescens) that have been surveyed for 25 years on their breeding grounds at the Hubbard Brook Experimental Forest in New Hampshire, USA. The intensive data collection efforts allow us to compare our estimates to estimates derived from capture–recapture data. Our model performed well in estimating population abundance and density‐dependent rates of annual recruitment/immigration. Estimates of local carrying capacity and per capita recruitment of yearlings were consistent with those published in other studies. However, our model moderately underestimated annual survival probability of yearling and adult females and severely underestimates survival probabilities for both of these male stages. The most accurate and precise estimates will necessarily require some amount of intensive data collection efforts (such as capture–recapture). Integrated population models that combine data from both intensive and extensive sources are likely to be the most efficient approach for estimating demographic rates at large spatial and temporal scales.     

Who are we sampling? Apparent survival differs between methods in a secretive species

Survival is a fundamental parameter in population dynamics with increasing importance in the management and conservation strategies of wildlife populations. Survival probability in vertebrates is usually estimated by live‐encounter data obtained by means of physical mark–capture–recapture protocols. Non‐invasive acoustic marking relying on individual‐specific features of signals has been alternatively applied as a marking technique, especially in secretive species. Nevertheless, to date no research has compared survival rate estimates obtained by acoustic and physical marking. We estimated half‐yearly and annual survival and recapture rates of a secretive and threatened passerine, the Dupont's lark Chersophilus duponti, using two separate live‐encounter data sets of males collected simultaneously by physical and acoustic marking in the same study area. The separate analysis of both methods led to different model structures, since transient individuals had to be accounted for in the acoustic marking but not in the physical marking data set. Furthermore, while reencounter probabilities did not differ between methods, survival estimates employing physical marking were lower than those obtained acoustically, especially between the postbreeding and the breeding period when the apparent survival of colour‐banded birds was twice as low as for acoustic marking. The combination of marking methods suggested the existence of different subsets of individuals differentially sampled within the population: whereas colour‐banded males seemed to represent the territorial fraction of the population, both resident and floater individuals were probably detected by acoustic marking. Using traditional mark–recapture methods exclusively could have misled our estimates of survival rates, potentially affecting prospective predictions of population dynamics. Acoustic marking has been poorly applied in mark–recapture studies, but might be a powerful complement to obtain accurate estimates of fundamental demographic parameters such as survival and dispersal.     

Climate change and habitat heterogeneity drive a population increase in Common Buzzards Buteo buteo through effects on survival

The effect of changing climatic conditions on wild populations has been the subject of much recent research. Most attention has been on the direct effects of climate changes on species of lower trophic levels and on the negative consequences of climate change. However, a deeper understanding of how climate change affects apex predators is vital, as they are keystone species that have a disproportionate effect on ecosystems. Studying survival in an apex predator requires individual‐based data from long‐term studies and is complicated by the integration of climatic effects on lower trophic levels. Here we assess how climate affects the survival of the Common Buzzard Buteo buteo. We analysed the survival of 670 males and 669 females over the period 1989–2011, during which time our study population quadrupled. We used mark–recapture survival analysis of individual resightings of breeding adults to identify the environmental factors best explaining survival. A decrease in the North Atlantic Oscillation (NAO) index increased survival to an extent that largely explains the population increase. This might be caused by higher Common Vole Microtus arvalis survival in drier conditions and under snow cover. Buzzard survival appeared to increase more for males than for females, possibly due to the males' higher sensitivity to winter food availability resulting from their smaller body mass. However, we also found that the effect of NAO strongly depended on the area in which individuals lived, especially for females. This may have been caused by the recolonization of Eagle Owls Bubo bubo in some parts of our study area. This study suggests that climatic changes can have complex effects on species of higher trophic levels via an interaction with their prey.     

Testing traditional assumptions about regional migration in bats

While some bats cover long distances during migration, moving thousands of kilometers, most migratory bats are considered regional migrants, thought to move relatively short distances (<?500 km) between hibernacula and maternity sites. However, behavior can vary considerably among species and our understanding of these movements has largely been limited to banding studies or detailed tracking of small numbers of bats by aircraft. Inferring population-wide behavior from small samples is difficult and can introduce bias. We tagged 108 Indiana bats (Myotis sodalis) in the Midwestern US and used a regional network of radiotelemetry receivers to study movement patterns. With this dataset, we tested the following traditional generalizations about regional migrants: (1) bats move away from hibernacula in spring in all directions with known maternity roosts, e.g., in a star-like pattern; (2) bats follow linear landscape features; (3) long-distance movements are uncommon; and (4) autumn migration comprises a single movement from summer maternity site to winter hibernaculum. In spring, bats left the hibernaculum immediately and primarily moved north despite available maternity roosts in all directions. We found no evidence that bats follow rivers, the predominant linear element in the landscape. Only six tagged bats traveled >?100 km, suggesting that longer-distance movements may be outliers. In autumn, only two bats visited multiple known hibernacula, and after swarming, some females moved >?100 km to areas without known hibernacula. Common generalizations about regional migrant movements may not be representative of population behavior and care should be taken with respect to management decisions based on those assumptions.     

The demography of an increasing insular Eurasian Scops Owl (Otus scops) population in western France

Rapid population declines of many long-distance Afro-Palaearctic migratory bird species are ongoing across Europe but the demographic drivers are often poorly understood, thereby limiting the development of appropriate conservation actions. Using long-term population monitoring (39 years), capture–mark–recapture data and a matrix model, we estimated demographic parameters and the effect of climate variables on adult survival, and modelled the dynamics of an increasing population of Eurasian Scops Owls Otus scops in a landscape with agricultural abandonment in western France. The observed mean annual population growth rate was 1.055 (from 68 to 523 territorial males between 1981 and 2019). Over the study period, clutch size and hatching success were stable, but fledging success and breeding success showed slight negative trends, probably due to density-dependence. Survival varied with age, with an increase during early life and evidence for rapid senescence from 4 years old. Adult survival remained stable and was positively linked to the amount of autumn rainfall in the Sahel and to the winter North Atlantic Oscillation. Survival of younger age-classes made the largest contribution to the variance of the population growth rate, followed by clutch size, fledging success and survival of older birds. Such a long-term population increase in a landscape where intensive agriculture has decreased by 64.6% sheds some new light on the causes of the decline of European Scops Owl and other Afro-Palaearctic bird populations. We infer some of the possible causes of this large-scale decline, in particular food shortage, and discuss conservation measures that could be applicable to reverse this trend.     

Spatial patterns in age- and colony-specific survival in a long-lived seabird across 14 contrasting colonies

Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species due to variation in underlying environmental processes. If environmental processes are spatially correlated, nearby populations are expected to have more similar demographic rates than those further apart. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal for studying spatial patterns in demographic rates and their effects on local population dynamics. Here we explored variation in age-dependent survival probabilities across 14 colonies of Herring Gulls Larus argentatus breeding along the Dutch North Sea coast. We used long-term mark–recapture data of marked fledglings to estimate survival, and estimated spatial autocorrelation of survival probabilities. We assessed whether survival until recruitment age or until 10 years old (close to their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north-to-south gradient in survival probability, with lower juvenile but higher adult survival in northern colonies than southern colonies, whereas the spatial pattern of immature survival was less distinct. Neither recruitment nor the proportion of 10-year-old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics.     

Lizards in the suburbs: a single-garden study of a small endemic New Zealand skink (Oligosoma aeneum)

Detailed investigations of ecology and life history of lizards in New Zealand/Aotearoa are needed to inform their conservation and management. An early demographic study of copper skinks (Oligosoma aeneum) in a suburban garden was undertaken in Lower Hutt using mark–recapture methods, sampling weekly from March 1971 to December 1973. Oligosoma aeneum were seen on 1372 occasions, with 972 captures of 169 individuals. The maximum snout–vent length was 66 mm, 33% of skinks had complete tails, and colour differences suggested sexual signalling and warrant further study. Most captures occurred over November–March, with fewest over June–August. The estimated spring/summer population size in the garden (± SEM) was 83.6 (± 9.4) skinks, and the annual survival rate (± SEM) was 38.0% (± 16.0%). This is one of the few New Zealand lizard studies that have extended through all months of the year and it adds to limited information on lizard populations in suburban areas.     

Grizzly bear population vital rates and trend in the Northern Continental Divide Ecosystem,Montana

We estimated grizzly bear (Ursus arctos) population vital rates and trend for the Northern Continental Divide Ecosystem (NCDE), Montana, between 2004 and 2009 by following radio-collared females and observing their fate and reproductive performance. Our estimates of dependent cub and yearling survival were 0.612 (95% CI = 0.300–0.818) and 0.682 (95% CI = 0.258–0.898). Our estimates of subadult and adult female survival were 0.852 (95% CI = 0.628–0.951) and 0.952 (95% CI = 0.892–0.980). From visual observations, we estimated a mean litter size of 2.00 cubs/litter. Accounting for cub mortality prior to the first observations of litters in spring, our adjusted mean litter size was 2.27 cubs/litter. We estimated the probabilities of females transitioning from one reproductive state to another between years. Using the stable state probability of 0.322 (95% CI = 0.262–0.382) for females with cub litters, our adjusted fecundity estimate (m_x) was 0.367 (95% CI = 0.273–0.461). Using our derived rates, we estimated that the population grew at a mean annual rate of approximately 3% (λ = 1.0306, 95% CI = 0.928–1.102), and 71.5% of 10,000 Monte Carlo simulations produced estimates of λ > 1.0. Our results indicate an increasing population trend of grizzly bears in the NCDE. Coupled with concurrent studies of population size, we estimate that over 1,000 grizzly bears reside in and adjacent to this recovery area. We suggest that monitoring of population trend and other vital rates using radioed females be continued. © 2011 The Wildlife Society.