Capture-recapture Models Research Articles

Northern brown bandicoot (

Despite the ongoing collapse of native mammal populations across northern Australia, the paucity of robust estimates of population density limits our capacity to identify and understand population change. Here we aimed to provide the first estimates of native mammal density on the Tiwi Islands – one of Australia’s largest remaining refuge areas for native mammals. We conducted intensive live-trapping at four sites that represent varying combinations of fire frequency, feral cat density and feral herbivore presence. We used spatially-explicit capture-recapture models to investigate the density of common brushtail possum (Trichosurus vulpecula) and northern brown bandicoot (Isoodon macrourus). Compared with mainland northern Australia, populations of common brushtail possum and northern brown bandicoot have remained relatively healthy on the Tiwi Islands. Common brushtail possum density was significantly higher on Bathurst Island (1.06 possum ha−1) compared with Melville Island (0.32 possum ha−1), whereas northern brown bandicoot density varied across all four sites (ranging from 0.04 to 0.34 bandicoot ha−1). Unexpectedly, the very frequently burnt Ranku site (Bathurst Island) continues to support healthy populations of both species. These density estimates provide critical information for identifying and understanding future population change for two species that have suffered marked declines across the Australian monsoon tropics. Although the lack of replication limits our ability to draw conclusions regarding the ecological constraints of these mammal populations, our density observations align with a recent conceptual model postulating that the persistence of native mammal populations across northern Australian savannas reflects a complex, but spatially-variable interplay of ‘bottom-up’ and ‘top-down’ processes.

A Novel Approach to Estimate the Population of Unmarked Social Animal Using Camera Traps Photo-Captures

Robust population estimation is indispensable for well-informed management and conservation of species. Capture-recapture models provide a robust framework for density estimation of animals with unique identifying features. The challenge is amplified for group-living species lacking identifiable marks where both the number of groups and number of individuals needs to be estimated simultaneously. We developed a model to estimate the population of group-living animals using a hierarchical clustering approach. We used weighted geographical distance and probability of missing an individual from photo-capture sequence to estimate number of groups and individuals in a group. We simulated scenarios with a varying number of capture sequence to test the effect of number of sequences on a detection probability and group-size. We applied the proposed method on a group living, unidentifiable canid, dhole (Cuon alpinus) following a multidisciplinary approach. We examined the average radius estimated from clustering method against home-range radius obtained from GPS-collared individuals. Additionally, we compared population estimates with individuals identified through molecular tools. Simulations showed there was no substantial change in the number of individuals estimated with the number of photo-capture sequences. The efficacy of our model was more than 70% until the ratio of the radii of the pack operating area and pack range centres were less than 0.8. The spatial extent and population estimate derived from clustering model was comparable with GPS telemetry data and individuals identified using molecular methods. Our model would broaden the scope of the applicability of camera trap studies for social species with uniquely unidentifiable individuals. With assumptions like territoriality, independent captures and cohesion of the study species, this model can aid in the monitoring and conservation of rare, endangered species like dholes, which otherwise pose a challenge to managers and conservation practitioners.

Jaguar (Panthera onca) density and tenure in a critical biological corridor.

We estimated jaguar density and tenure, and investigated ranging behavior, using camera traps across the Maya Forest Corridor, a human-influenced landscape in central Belize that forms the only remaining connection for jaguar populations inhabiting two regional forest blocks: the Selva Maya and the Maya Mountain Massif. Jaguars were ubiquitous across the study area. Similar to the neighboring Selva Maya, mean density ranged from 1.5 to 3.1 jaguars per 100 km2, estimated by spatial capture-recapture models. Cameras detected almost twice as many males as females, probably reflecting detection bias, and males ranged more widely than females within the camera grid. Both sexes crossed two major rivers, while highway crossings were rare and male-biased, raising concern that the highway could prevent female movement if traffic increases. Jaguars were more transient where the landscape was fragmented with settlements and agriculture than in contiguous forest. Compared with jaguars in the protected forests of the Maya Mountains, jaguars in central Belize displayed a lower potential for investment in intraspecific communication, indicative of a lower quality landscape; however, we did detect mating behavior and juveniles. Tenure of individuals was shorter than in the protected forests, with a higher turnover rate for males than females. At least three-quarters of reported jaguar deaths caused by people were male jaguars, and the majority was retaliation for livestock predation. Jaguars seem relatively tolerant to the human-influenced landscape of central Belize. However, intensification of game hunting and lethal control of predators would threaten population persistence, while increased highway traffic and clear-cutting riparian forest would severely limit the corridor function. Our results show that the viability of the corridor, and thus the long-term survival of jaguar populations in this region, will depend on appropriate land-use planning, nonlethal control of livestock predators, enforcement of game hunting regulations, and wildlife-friendly features in future road developments.

Density Dependence and Adult Survival Drive Dynamics in Two High Elevation Amphibian Populations

Amphibian conservation has progressed from the identification of declines to mitigation, but efforts are hampered by the lack of nuanced information about the effects of environmental characteristics and stressors on mechanistic processes of population regulation. Challenges include a paucity of long-term data and scant information about the relative roles of extrinsic (e.g., weather) and intrinsic (e.g., density dependence) factors. We used a Bayesian formulation of an open population capture-recapture model and >30 years of data to examine intrinsic and extrinsic factors regulating two adult boreal chorus frogs (Pseudacris maculata) populations. We modelled population growth rate and apparent survival directly, assessed their temporal variability, and derived estimates of recruitment. Populations were relatively stable (geometric mean population growth rate >1) and regulated by negative density dependence (i.e., higher population sizes reduced population growth rate). In the smaller population, density dependence also acted on adult survival. In the larger population, higher population growth was associated with warmer autumns. Survival estimates ranged from 0.30–0.87, per-capita recruitment was <1 in most years, and mean seniority probability was >0.50, suggesting adult survival is more important to population growth than recruitment. Our analysis indicates density dependence is a primary driver of population dynamics for P. maculata adults.

Spatial capture-recapture with random thinning for unidentified encounters.

Spatial capture–recapture (SCR) models have increasingly been used as a basis for combining capture–recapture data types with variable levels of individual identity information to estimate population density and other demographic parameters. Recent examples are the unmarked SCR (or spatial count model), where no individual identities are available and spatial mark–resight (SMR) where individual identities are available for only a marked subset of the population. Currently lacking, though, is a model that allows unidentified samples to be combined with identified samples when there are no separate classes of “marked” and “unmarked” individuals and when the two sample types cannot be considered as arising from two independent observation models. This is a common scenario when using noninvasive sampling methods, for example, when analyzing data on identified and unidentified photographs or scats from the same sites.Here we describe a “random thinning” SCR model that utilizes encounters of both known and unknown identity samples using a natural mechanistic dependence between samples arising from a single observation model. Our model was fitted in a Bayesian framework using NIMBLE.We investigate the improvement in parameter estimates by including the unknown identity samples, which was notable (up to 79% more precise) in low‐density populations with a low rate of identified encounters. We then applied the random thinning SCR model to a noninvasive genetic sampling study of brown bear (Ursus arctos) density in Oriental Cantabrian Mountains (North Spain).Our model can improve density estimation for noninvasive sampling studies for low‐density populations with low rates of individual identification, by making use of available data that might otherwise be discarded.

Combining live and lethal trapping to inform the management of alien invasive rodent populations in a tropical montane forest

On large inhabited islands where complete eradication of alien invasive rodents through the use of poison delivery is often not practical or acceptable, mechanical trapping may represent the only viable option to reduce their impact in areas of high biodiversity value. However, the feasibility of sustained rodent control by trapping remains uncertain under realistic operational constraints. This study aimed to assess the effectiveness of non-toxic rat control strategies through a combination of lethal and live-trapping experiments, and scenario modelling, using the example of a remote montane rainforest of New Caledonia. Rat densities, estimated with spatially-explicit capture-recapture models, fluctuated seasonally (9.5–33.6 ind.ha-1). Capture probability (.01–.25) and home range sizes (HR95, .23–.75 ha) varied greatly according to trapping session, age class, sex and species. Controlling rats through the use of lethal trapping allowed maintaining rat densities at ca. 8 ind.ha-1 over a seven-month period in a 5.5-ha montane forest. Simulation models based on field parameter estimates over a 200-ha pilot management area indicated that without any financial and social constraints, trapping grids with the finest mesh sizes achieved cumulative capture probabilities > .90 after 15 trapping days, but were difficult to implement and sustain with the local workforce. We evaluated the costs and effectiveness of alternative trapping strategies taking into account the prevailing set of local constraints, and identified those that were likely to be successful. Scenario modelling, informed by trapping experiments, is a flexible tool for informing the design of sustainable control programs of island-invasive rodent populations, under idiosyncratic local circumstances.

Spatial capture-recapture with multiple noninvasive marks: An application to camera-trapping data of the European wildcat (Felis silvestris) using R package multimark.

In Switzerland, the European wildcat (Felis silvestris), a native felid, is protected by national law. In recent decades, the wildcat has slowly returned to much of its original range and may have even expanded into new areas that were not known to be occupied before. For the implementation of efficient conservation actions, reliable information about the status and trend of population size and density is crucial. But so far, only one reliable estimate of density in Switzerland was produced in the northern Swiss Jura Mountains. Wildcats are relatively rare and elusive, but camera trapping has proven to be an effective method for monitoring felids. We developed and tested a monitoring protocol using camera trapping in the northern Jura Mountains (cantons of Bern and Jura) in an area of 100 km2. During 60 days, we obtained 105 pictures of phenotypical wildcats of which 98 were suitable for individual identification. We identified 13 individuals from both sides and, additionally, 5 single right‐sided flanks and 3 single left‐sided flanks that could not be matched to unique individuals. We analyzed the camera‐trap data using the R package multimark, which has been extended to include a novel spatial capture–recapture model for encounter histories that include multiple “noninvasive” marks, such as bilaterally asymmetrical left‐ and right‐sided flanks, that can be difficult (or impossible) to reliably match to individuals. Here, we present this model in detail for the first time. Based on a “semi‐complete” data likelihood, the model is less computationally demanding than Bayesian alternatives that rely on a data‐augmented complete data likelihood. The spatially explicit capture–recapture model estimated a wildcat density (95% credible interval) of 26 (17–36) per 100 km2 suitable habitat. Our integrated model produced higher abundance and density estimates with improved precision compared to single‐sided analyses, suggesting spatially explicit capture–recapture methods with multiple “noninvasive” marks can improve our ability to monitor wildcat population status.

A spatial capture–recapture model to estimate call rate and population density from passive acoustic surveys

Abstract Spatial capture–recapture (SCR) models are commonly used to estimate animal population density from detections and subsequent redetections of individuals across space. In particular, acoustic SCR models deal with detections of animal vocalisations across an array of acoustic detectors. Previously published acoustic SCR methods either estimate call density (calls per unit space per unit time) rather than animal density itself, require an independently estimated call rate to estimate animal density, or discard data from all but one detected call from each individual. In this manuscript, we develop a new spatial capture–recapture model that estimates both call rate and animal density from the acoustic survey alone, without requiring an independently estimated call rate. Our approach therefore alleviates the need for the additional fieldwork of physically locating and monitoring individual animals. We illustrate our method and compare it to an existing approach using a simulation study and an application to data collected on an acoustic survey of the visually cryptic Cape peninsula moss frog Arthroleptella lightfooti. In the context of our acoustic survey, our calling animal density estimator has low bias, good precision and confidence intervals with appropriate coverage, yielding results that are consistent with previous studies of the same species. Our method can obtain accurate and precise estimates of animal density while eliminating the fieldwork burden associated with separately estimating call rate. We discuss how the development of our model's likelihood reveals a clear path to further extensions, which may incorporate features such as animal movement processes and uncertain individual identification.

Demographic and ecological correlates of a recovering tiger (Panthera tigris) population: Lessons learnt from 13-years of monitoring

Efforts are on to recover tiger populations range-wide, but we lack suitable metrics to characterise and evaluate such recoveries. Identifying such metrics requires an understanding of tiger population dynamics and its ecological correlates in either recovering populations or those exposed to anthropogenic influences. We monitored a recovering tiger population from 2004 to 2017 in Rajaji National Park, India. Using photographic data and spatial capture-recapture models in an inviolate site vacated by pastoralists (zone 1), we identified demographic parameters of a recovering population. By contrasting it with a site that is presently occupied by pastoralists (zone 3) and one that is isolated (zone 3), we identified conditions facilitating recovery. In zone 1, connected to a large source population in Corbett Tiger Reserve, density increased from 2.08 tigers/100 km2 to 7.07 tigers/100 km2 corresponding to an annual growth rate of 4.5%. Density also increased in zone 2 (2.6 tigers/100 km2 to 6.22 tigers/100 km2), but estimated apparent survival was 0.47 against 0.81 in zone 1. Recovery in zone 1 was accompanied by increased survival of females, while female tenure was shorter in zone 2. Due to the lack of functional connectivity, tigers in zone 3 are facing local extinction. Our results demonstrate that creating inviolate spaces to secure breeding populations and maintaining landscape-wide connectivity to expand breeding cores is critical for recovery. We highlight that relying solely on population increase may lead to unreliable inferences about population performance and instead suggest tracking survival and female land tenure to qualify recovery and success of conservation interventions.

More than just refuelling: lengthy stopover and selection of departure weather by sandpipers prior to transoceanic and transcontinental flights

The evolutionary and behavioural ecology of migratory birds has received much theoretical and empirical attention. We contribute to this field by contrasting the weather at departure and stopover durations of a long‐distance migratory sandpiper prior to initiating lengthy transoceanic vs. transcontinental flights of potentially variable duration. Transoceanic flights provide few if any stopover options. We predicted that transoceanic migrants should therefore be more selective of energetically favourable weather at departure and have longer stopover durations prior to departing, using time as a surrogate for cumulative fuel acquisition, compared with transcontinental migrants. We used recent advances in capture–recapture modelling to quantify how weather conditions, length of stay, including estimated residence time prior to capture, and age class correlated with daily departure probabilities of Semipalmated Sandpipers Calidris pusilla at a coastal and an inland stopover site at comparable latitude. As expected, departure probabilities from both sites were higher with increasing strength of tailwinds, and the strength of this effect was larger for birds facing transoceanic vs. transcontinental flights. Cloud cover and temperature conditions at departure converged between sites at intermediate values from different background distributions. Stopover durations at both sites were substantially longer than needed if the birds were pursuing a simple tactic of arrive–fatten–leave at the stopover site. We infer that both sites provided high levels of both food and safety relative to other stages in the birds’ annual cycle, favouring lengthy stopovers and subsequent use of lengthy flights from both sites. Our study shows that recent advances of capture–recapture models can provide additional resolution to studies of the migration strategies of birds and refine our perspective on global patterns of migration routes and stopover decisions.

Abundance and survival estimates of the southeastern Pacific humpback whale stock from 1991–2006 photo-identification surveys in Ecuador

Southeastern Pacific humpback whales (Breeding Stock G) breed along the northwestern coast of South America and farther north up to CostaRica. Photo-identification surveys conducted aboard whalewatching vessels during the migration/breeding season from June to September between1991 and 2006 off the coast of Ecuador (2°S, 81°W) have produced a database of 1,511 individual whales. Comparisons of photographs produced190 between-year re-sightings of 155 individual whales. Closed and open capture-recapture models were used to estimate abundance and survival.The best estimate of abundance in 2006 with the Chapman modified-Petersen was 6,504 (95% CI: 4,270–9,907; CV = 0.21). Abundance estimatesfrom open population models were considerably lower due to heterogeneity in capture probability which produced a ‘transient’ effect. Our bestestimate of true survival was 0.919 (95% CI: 0.850–0.958). Heterogeneity most likely occurred from inter-annual variation in sampling and unknownstructure and variation in the migration timing and corridor. A more extensive collaborative effort including other wintering areas further north aswell as integrating breeding-feeding data will help to reduce heterogeneity and increase precision in abundance and survival estimates.

Abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa.

Coastally distributed dolphin species are vulnerable to a variety of anthropogenic pressures, yet a lack of abundance data often prevents data-driven conservation management strategies from being implemented. We investigated the abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa, from the Goukamma Marine Protected Area (MPA) to the Tsitsikamma MPA, between 2014 and 2016. During this period, 662.3h of boat-based photo-identification survey effort was carried out during 189 surveys. The sighting histories of 817 identified individuals were used to estimate abundance using capture-recapture modelling. Using open population (POPAN) models, we estimated that 2,155 individuals (95% CI: 1,873–2,479) occurred in the study area, although many individuals appeared to be transients. We recorded smaller group sizes and an apparent decline in abundance in a subset of the study area (Plettenberg Bay) compared to estimates obtained in 2002–2003 at this location. We recorded declines of more than 70% in both abundance and group size for a subset of the study area (Plettenberg Bay), in relation to estimates obtained in 2002–2003 at this location. We discuss plausible hypotheses for causes of the declines, including anthropogenic pressure, ecosystem change, and methodological inconsistencies. Our study highlights the importance of assessing trends in abundance at other locations to inform data-driven conservation management strategies of T. aduncus in South Africa.

Abundance, survival and population growth of killer whales Orcinus orca at subantarctic Marion Island

Killer whales, Orcinus orca, are a cosmopolitan species with large ecological and demographic variation across populations. Population‐specific demographic studies are, therefore, crucial in accurately assessing the status and trends of local killer whale populations. Such studies require long‐term datasets and remain scarce, particularly in the Southern Ocean where detailed population specific studies have only been conducted at a single archipelago – Îles Crozet. Here, we analysed 12 years of capture–recapture data (comprising nearly 90 000 identification photographs taken from 2006 to 2018) of killer whales at subantarctic Marion Island (46°54′S, 37°45′E) to estimate the abundance, survival and growth rate of this population. Demographic parameters were estimated using multistate capture recapture models, and Pradel Survival‐Lambda and POPAN single‐state models implemented in the program MARK. Annual survival probability (0.98 [95% CI: 0.96–0.99]) was constant over time, and no important differences between sexes and age‐classes (calves, juveniles, adults) were found. This estimate of survival suggests a life expectancy of approximately 48 years. Realised mean population growth rate (λ) was 1.012 (0.987–1.037) with an estimated population size of 54 (54–60) individuals and a mean calving rate of 0.13 (0.06–0.20) calves born per year per reproductive female. The survival and reproduction rates of killer whales at Marion Island are similar to those of killer whale populations in the eastern North Pacific, Norway and Îles Crozet. However, subtle differences in survival and reproduction rates are present. These are likely the result of local differences in resource abundances, historical impacts on social structure and/or stressors. Also, the presence and scale of fisheries (legal and illegal) in the area may provide opportunities for direct interactions with fishing activities impacting survival and reproduction rates.

Avances en foto-identificación automatizada de fauna silvestre

La foto-identificación de especies silvestres es un recurso base para la obtención de información necesaria para diversas tareas de investigaciones biológicas. Hoy en día el crowdsourcing y la ciencia ciudadana están comenzando a desempeñar un rol importante en la recopilación de datos científicos. Esta fuente de datos permite aumentar considerablemente el número de registros en la base de muestreo de diferentes proyectos científicos, especialmente los relacionados con los modelos de capturarecaptura fotográfica de vida silvestre. No obstante, mientras que se aumenta la cantidad de datos recopilados de fuentes no científicas, se presenta un nuevo desafío, el procesamiento masivo de manera ágil y eficiente, que permita limpiar y seleccionar los datos relevantes para las siguientes etapas.Este trabajo aborda la automatización de la primer etapa del proceso de foto-identificación de cetáceos, el cual se trata de la detección de la presencia o ausencia de la región de interés en la imagen (ROI). Para ello, se especializó una red neuronal convolucional de propósito general (Mask R-CNN) con imágenes de delfines de la especie Cephalorhynchus commersonii recolectadas en diferentes sitios de la costa patagónica durante un período de siete años.

Using Continuous-Time Spatial Capture-Recapture models to make inference about animal activity patterns.

Quantifying the distribution of daily activity is an important component of behavioral ecology. Historically, it has been difficult to obtain data on activity patterns, especially for elusive species. However, the development of affordable camera traps and their widespread usage has led to an explosion of available data from which activity patterns can be estimated.Continuous‐time spatial capture–recapture (CT SCR) models drop the occasion structure seen in traditional spatial and nonspatial capture–recapture (CR) models and use the actual times of capture. In addition to estimating density, CT SCR models estimate expected encounters through time. Cyclic splines can be used to allow flexible shapes for modeling cyclic activity patterns, and the fact that SCR models also incorporate distance means that space–time interactions can be explored. This method is applied to a jaguar dataset.Jaguars in Belize are most active and range furthest in the evening and early morning and when they are located closer to the network of trails. There is some evidence that females have a less variable pattern than males. The comparison between sexes demonstrates how CT SCR can be used to explore hypotheses about animal behavior within a formal modeling framework.SCR models were developed primarily to estimate and model density, but the models can be used to explore processes that interact across space and time, especially when using the CT SCR framework that models the temporal dimension at a finer resolution.

Relative influence of wild prey and livestock abundance on carnivore-caused livestock predation.

Conservation conflict over livestock depredation is one of the key drivers of large mammalian carnivore declines worldwide. Mitigating this conflict requires strategies informed by reliable knowledge of factors influencing livestock depredation. Wild prey and livestock abundance are critical factors influencing the extent of livestock depredation. We compared whether the extent of livestock predation by snow leopards Panthera uncia differed in relation to densities of wild prey, livestock, and snow leopards at two sites in Shey Phoksundo National Park, Nepal. We used camera trap‐based spatially explicit capture–recapture models to estimate snow leopard density; double‐observer surveys to estimate the density of their main prey species, the blue sheep Pseudois nayaur; and interview‐based household surveys to estimate livestock population and number of livestock killed by snow leopards. The proportion of livestock lost per household was seven times higher in Upper Dolpa, the site which had higher snow leopard density (2.51 snow leopards per 100 km2) and higher livestock density (17.21 livestock per km2) compared to Lower Dolpa (1.21 snow leopards per 100 km2; 4.5 livestock per km2). The wild prey density was similar across the two sites (1.81 and 1.57 animals per km2 in Upper and Lower Dolpa, respectively). Our results suggest that livestock depredation level may largely be determined by the abundances of the snow leopards and livestock and predation levels on livestock can vary even at similar levels of wild prey density. In large parts of the snow leopard range, livestock production is indispensable to local livelihoods and livestock population is expected to increase to meet the demand of cashmere. Hence, we recommend that any efforts to increase livestock populations or conservation initiatives aimed at recovering or increasing snow leopard population be accompanied by better herding practices (e.g., predator‐proof corrals) to protect livestock from snow leopard.

Investigating effects of soil chemicals on density of small mammal bioindicators using spatial capture-recapture models.

Monitoring the ecological impacts of environmental pollution and the effectiveness of remediation efforts requires identifying relationships between contaminants and the disruption of biological processes in populations, communities, or ecosystems. Wildlife are useful bioindicators, but traditional comparative experimental approaches rely on a staunch and typically unverifiable assumption that, in the absence of contaminants, reference and contaminated sites would support the same densities of bioindicators, thereby inferring direct causation from indirect data. We demonstrate the utility of spatial capture-recapture (SCR) models for overcoming these issues, testing if community density of common small mammal bioindicators was directly influenced by soil chemical concentrations. By modeling density as an inhomogeneous Poisson point process, we found evidence for an inverse spatial relationship between Peromyscus density and soil mercury concentrations, but not other chemicals, such as polychlorinated biphenyls, at a site formerly occupied by a nuclear reactor. Although the coefficient point estimate supported Peromyscus density being lower where mercury concentrations were higher (β = –0.44), the 95% confidence interval overlapped zero, suggesting no effect was also compatible with our data. Estimated density from the most parsimonious model (2.88 mice/ha; 95% CI = 1.63–5.08), which did not support a density-chemical relationship, was within the range of reported densities for Peromyscus that did not inhabit contaminated sites elsewhere. Environmental pollution remains a global threat to biodiversity and ecosystem and human health, and our study provides an illustrative example of the utility of SCR models for investigating the effects that chemicals may have on wildlife bioindicator populations and communities.

A spatial capture–recapture model with attractions between individuals

AbstractOver the past two decades there have been many advancements in modeling capture–recapture (CR) data to account for emerging data collection technology and techniques. Spatial capture–recapture (SCR) models have been introduced to estimate population size and numerous other demographic parameters from spatially explicit CR data. Recently SCR models have also begun incorporating realistic animal movement to account for individual dispersion and attraction to resources. While some species of animals are known to exhibit attractive behavior, nearly all SCR models assume complete independence among individual's movement and capture probability. In this article, we introduce an SCR model which allows for attractions between individuals via their daily location. We demonstrate via a simulation study that accounting for the attractions specified by our model, when present, can improve population size estimation. In addition, we apply our model to an iconic SCR dataset to estimate the population size and attraction parameters of a Bengal tiger (Panthera tigris tigris) population.

Elusive cats in our backyards: persistence of the North Chinese leopard (Panthera pardus japonensis) in a human-dominated landscape in central China.

The North Chinese leopard (Panthera pardus japonensis), the least‐known big cat, disappeared in most historical range for decades, following the development of modern civilization. Unfortunately, we have scarce knowledge about the status of this big cat so far, apart from anecdotal reports. In this study, we investigated density, distribution, and habitat use of the leopard, the apex predator, in a complex forest landscape in the Loess Plateau. We used a camera‐trapping network to obtain population estimates for leopards over 2 years through spatially explicit capture–recapture models. Our results, based on maximum likelihood and Bayesian/MCMC methods, reveal that the largest wild population of the leopard was found widely distributed in remnant forests in central Loess plateau. The population is increasing in our study area, and the density of leopards (1.70 (SE = 0.48) − 2.40 (SE = 0.67)/100 km2) is higher than other areas of China. According to the analysis of 2 seasonal occupancy models, prey species drive partially the leopard habitat use, predicting that the big cat thrives from the recovery of prey community. However, human disturbances, especially oil wells, seem to have negative impacts on the habitat use of leopards. Specifically, it is necessary to have joint efforts by the government and researchers to improve human disturbances management and prey species population density, as well as strengthen the investment in research on the North Chinese leopard, which could all further strengthen protection ability and ensure the long‐term survival of this species.

Costs and Precision of Fecal DNA Mark–Recapture versus Traditional Mark–Resight

ABSTRACTWildlife managers often need to estimate population abundance to make well‐informed decisions. However, obtaining such estimates can be difficult and costly, particularly for species with small populations, wide distributions, and spatial clustering of individuals. For this reason, DNA surveys and capture–recapture modeling has become increasingly common where direct observation is consistently difficult or counts are small or variable. We compared the precision, as indicated by the coefficient of variation (CV), and cost‐effectiveness of 2 methods to estimate abundance of desert bighorn sheep (Ovis canadensis nelsoni) populations: traditional ground‐based mark–resight and fecal DNA capture–recapture. In the Marble Mountains in the Mojave Desert of southeastern California, USA, we conducted annual ground‐based mark–resight surveys and collected fecal samples at water sources concurrently during the dry seasons (Jun–Jul) of 2016 and 2017. Fecal DNA samples were genotyped to identify unique individuals. The Lincoln–Peterson bias‐corrected estimator and Huggins closed‐capture recapture models were used to estimate abundance for the ground‐based mark resight and fecal DNA capture–recapture, respectively. We compared costs between the 2 methods for our study and used simulations to estimate costs for a variety of possible sampling scenarios for our study system based on field‐based estimates. Population abundance estimates from fecal DNA capture–recapture achieved much greater precision (CV = 5–7%) than estimates derived from ground‐based mark–resight (CV = 21–56%). Our simulations indicated that for a population of 100, 2 sampling occasions, and resight probability of 0.20, the lowest CV obtained by mark–resight was approximately 12%. We predict the cost of abundance estimates for this level of precision (CV = 12%) from fecal DNA capture–recapture would be 28% of the cost of ground‐based mark–resight (i.e., a 72% cost reduction). We conclude that fecal DNA capture–recapture is a highly cost‐effective alternative for estimating abundance of relatively small populations (≤300) of desert bighorn sheep. More broadly, integrating simulated study designs with cost analyses provides a tool to identify the most effective method for estimating abundance over a wide variety of sampling scenarios. © 2020 The Wildlife Society.