Examining dynamic occupancy of gray wolves in Idaho after a decade of managed harvest

Abstract

Gray wolves (Canis lupus) were reintroduced to Idaho, USA, in 1995–1996. The removal of Endangered Species Act protections in 2011 transferred wolf management to the state where wolves were subsequently classified as a harvested (i.e., hunted, trapped) big game species. We implemented a camera‐based survey across Idaho from 2016–2021 as part of a population monitoring program. We used the resulting camera images in multi‐year, dynamic and single‐season occupancy models to examine potential changes in the asymptotic proportion of area occupied by wolves and assess the effect of cumulative wolf harvest from 2016–2021 on occupancy in the last year of the study, 2021. We also wanted to understand how habitat, prey, humans, harvest, livestock, and prey‐related wolf removals affected wolf occupancy through their effects on colonization and extinction of occupancy cells through time. Statewide wolf occupancy did not change appreciably over the course of our study, with the proportion of survey cells occupied at an estimated high of 0.44 ± 0.03 (SE) in 2018 and a low of 0.39 ± 0.03 in 2020. Wolf colonization (i.e., probability that a cell switched from unoccupied to occupied between years) was positively associated with forest cover, images of humans, and the percent of neighboring cells that were occupied. Cell extinction (i.e., probability of switching from occupied to unoccupied between years) was negatively associated with neighboring cell occupancy. There were non‐linear relationships between wolf harvest, colonization, and extinction. The single‐season occupancy model demonstrated a positive relationship between harvest and occupancy at low to moderate levels of harvest (10–30%), but there was also evidence that high levels of harvest (>30%) reduce occupancy. Our results indicate that although harvest might influence wolf occupancy at local scales, wolf occupancy remained relatively constant across the state and wolves remained well distributed across Idaho during the study.