Integrating multiple datasets into spatially-explicit capture-recapture models to estimate the abundance of a locally scarce felid

Abstract

The conservation of animal populations often requires the estimation of population size. Low density and secretive behaviour usually determine scarce data sources and hampers precise abundance estimations of carnivore populations. However, joint analysis of independent scarce data sources in a common modeling framework allows unbiased and precise estimates of population parameters. We aimed to estimate the density of the European wildcat (Felis silvestris) in a protected area of Spain, by combining independent datasets in a spatially-explicit capture-recapture (SCR) framework. Data from live-capture with individual identification, camera-trapping without individual identification and radio-tracking concurrently obtained were integrated in a joint SCR and count data model. Ten live captures of five wildcats were obtained with an effort of 2034 trap-days, whereas seven wildcat independent events were recorded in camera traps with 3628 camera-days. Two wildcats were radio-tagged and telemetry information on their movements was obtained. The integration of the different data sources improved the precision obtained by the standard SCR model. The mean (± SD) density estimated with the integrated model (0.038 ± 0.017 wildcats/km2, 95% highest posterior density 0.013–0.082) is among the lowest values ever reported for this species, despite corresponding to a highly protected area. Among the likely causes of such low density, low prey availability could have triggered an extinction vortex process. We postulate that the estimated low density could represent a common situation of wildcat populations in the southern Iberia, highlighting the need for further studies and urgent conservation actions in the furthermost southwestern range of this species in Europe.

An integrated spatial capture–recapture approach reveals the distribution of a cryptic carnivore in a protected area

“…We developed a hierarchical, integrated SCR model to estimate the abundance, distribution, and density of cougars in Yosemite (Ferreras et al, 2021; Linden et al, 2018; Royle & Young, 2008; Figure 2). In this integrated SCR model, we incorporated scat detections, which provided locations of known individuals, and remote camera detections of unknown individuals (sensu Ferreras et al, 2021) to increase the precision of activity center estimates and improve density estimates of cougars.…”

“…We developed a hierarchical, integrated SCR model to estimate the abundance, distribution, and density of cougars in Yosemite (Ferreras et al, 2021; Linden et al, 2018; Royle & Young, 2008; Figure 2). In this integrated SCR model, we incorporated scat detections, which provided locations of known individuals, and remote camera detections of unknown individuals (sensu Ferreras et al, 2021) to increase the precision of activity center estimates and improve density estimates of cougars. We used a nested approach, where we modeled the effects of survey year, sex of individual cougars, and spatial covariates on detection probability, analogous to finer scale space‐use and probability of detecting cougars during detection team surveys (i.e., within the 3 × 3 km or 9 km 2 , grid cell x ), and modeled the effects of vegetation on the occurrence of activity centers, the latent variable s i that is analogous to broader scale space‐use of cougars and their distribution and density throughout the model state‐space (i.e., within the 9 × 9 km or 81 km 2 , grid cell c ).…”

Genetic integrity of European wildcats: Variation across biomes mandates geographically tailored conservation strategies

“…Despite being more "natural", such landscapes provide fewer and less diversified resources and may be unsuitable for key prey species. This can lead to less dense wildcat populations (Ferreras et al, 2021) that, together with the presence of domestic cats in PAs (Sarmento et al, 2009), can increase the probability of hybridisation. This reduced effectiveness of PAs to conserve the wildcat's GI in Mediterranean areas, in contrast to the pattern detected for northern biomes, highlights once more the need to regionally adapt the wildcat's conservation action plans to the environmental and socio-cultural contexts of different European landscapes.…”

Occupancy data improves parameter precision in spatial capture–recapture models

“…The SCR-Counts model was used by Ferreras et al (2021) to estimate European wildcat Felis silvestris population size in Cabañeros National Park (Spain), demonstrating its applicability in extremely low densities. To the best of our knowledge, the SCR-Occ was only tested on simulated data, and therefore requires an implementation with real-life datasets (Kéry & Royle, 2021).…”

“…Two different spatial capture–recapture integrated models were presented, and tested with simulated data: (1) the integrated SCR‐Counts model, which integrates capture histories and count data without identification, and (2) the integrated SCR‐Occ model, which integrates of SCR and “occupancy” (detection/nondetection) data. The SCR‐Counts model was used by Ferreras et al ( 2021 ) to estimate European wildcat Felis silvestris population size in Cabañeros National Park (Spain), demonstrating its applicability in extremely low densities. To the best of our knowledge, the SCR‐Occ was only tested on simulated data, and therefore requires an implementation with real‐life datasets (Kéry & Royle, 2021 ).…”