Kill rates on native ungulates by Mexican gray wolves in Arizona and New Mexico

Abstract

AbstractMexican gray wolf (Canis lupus baileyi) reintroduction began in 1998 in Arizona, USA, with 11 individuals initially; wolves from this population dispersed into New Mexico, USA, the following year. Numbers of wolves have steadily increased (≥241 individuals in Dec 2022) and the size of the recovery area has expanded in both states. Understanding kill rates is fundamental to the recovery and management of Mexican wolves to properly maintain a healthy and sustainable population of wolves and their prey species. We used global positioning system (GPS) cluster analysis to locate kill sites and estimate kill rates on native ungulate prey taken in the recovery area by 10 Mexican wolf groups during winter (15 Feb–15 Mar) and 8 wolf groups during summer (15 Jun–15 Jul) in 2015–2017. Elk (Cervus canadensis) composed 94% of the native ungulates documented at Mexican wolf kill sites (n = 139); the remaining 6% were mule deer (Odocoileus hemionus; n = 9). Two‐thirds of all wolf‐killed native ungulates were elk calves. We estimated kill rates as ungulate biomass killed/wolf/day. From combined results for all years, we estimated that each Mexican wolf killed on average 9.0 ± 5.4 kg (±95% CI) of ungulate biomass per day during winter and 7.8 ± 6.2 kg during the summer. Our estimates of kill rates could be overestimated if Mexican wolves obtained a substantial amount of their biomass from scavenging, particularly during 4 months of hunting seasons (Sep–Dec) not captured in winter and summer. Using data from the first 2 years of the study (2015, 2016), we developed a logistic regression model to predict probability of an elk kill occurring at a GPS cluster as a function of hours spent by a collared wolf at that GPS cluster and size of the wolf group. Applying this model to the final year of the study (2017) resulted in similar numbers of predicted (n = 16.1 and 27.2 in winter and summer, respectively) and observed numbers (n = 15 and 26) of elk kills. Additionally, the demographic composition of the 2017 elk kills closely matched that of the previous 2 years. The results of this study indicate similar predation patterns of Mexican wolves to those of wolves in northern locations and can help wildlife managers plan for potential effects from a larger population of wolves across a broad area in Arizona and New Mexico.