Sex-specific population dynamics and demography of capercaillie (Tetrao urogallus L.) in a patchy environment

Abstract

Modeling the population dynamics of patchily distributed species is a challenge, particularly when inference must be based on incomplete and small data sets such as those from most species of conservation concern. Here, we develop an open population spatial capture–recapture (SCR) model with sex‐specific detection and population dynamics parameters to investigate population trend and sex‐specific population dynamics of a capercaillie (Tetrao urogallus) population in Switzerland living in eight distinct forest patches totaling 22 km2 within a region of 908 km2 and sampled via scat collection. Our model accounts for the patchy distribution of habitat and the uncertainty introduced by collecting data only every third year, while producing sex by patch population trajectories. The estimated population trajectory was a decline of 2% per year; however, the sex specificity of the model revealed a decline in the male population only, with no evidence of decline in the female population. The decline observed in males was explained by the demography of just two of the eight patches. Our study highlights the flexibility of open population SCR models for assessing population trajectories through time and across space and emphasizes the desirability of estimating sex‐stratified population trends especially in species of conservation concern.

A review of movement models in open population capture–recapture

“…The model is not neutral, but rather an extreme movement model with respect to what can be represented with a 2‐dimensional kernel that declines monotonically from the point of origin (i.e., all models considered here except for gamma and log‐normal distributions of radial distance; Figure 3). Independent relocation was applied by Augustine et al (2020) to a capercaillie Tetrao urogallus dataset, with random relocation restricted to the current habitat patch. Using natural boundaries avoided some arbitrariness, and their survival estimates were likely unbiased by movement because the entire habitat was searched, but the movement model itself remains arbitrary (actual dispersal may have been on a scale smaller or larger than the patch).…”

“…Paquet et al (2020) fixed the shape parameter of the marginal distribution of movements ‘for convergence/identifiability reasons’. Augustine et al (2020) used a kernel‐free approach for capercaillie Tetrao urogallus that we discuss later. Others have fitted open SECR models with static activity centres (Chandler et al, 2018; Chandler & Clark, 2014; Gardner et al, 2010; Whittington & Sawaya, 2015).…”