Patterns and Determinants of Mortality in Grey Wolves (Canis lupus)

Abstract

Background: Understanding mortality is crucial to predict the dynamics of animal populations, especially for long-lived species subjected to widespread human pressure. This is the case for the grey wolf (Canis lupus), yet local studies provide an incomplete view of the patterns and determinants of this process. Aims and Methods: We conducted a systematic review of the existing literature on grey wolf mortality across the species' distribution range (i.e., most of the Northern Hemisphere) to identify global patterns and potential differences across continents. Studies were analysed based on the type of information provided, including mortality rates, proportion of dead individuals by cause, and natural and human-related determinants of mortality. Results and Discussion: We found high global minimum annual mortality rates in wolves (0.31 ± 0.18), compared to those reported under low human persecution (< 0.2). Most deaths were linked to human activities, primarily deliberate (legal and illegal) killing (60% ± 25%). Europe reported a higher percentage of human-related deaths (86% ± 14%) than North America (66% ± 24%). This is likely due to higher anthropogenic pressures in Europe and differences in carcass detection methods between continents (opportunistic recovery in Europe vs. tracking of collared wolves in North America). However, the lack of data from areas with low human influence (e.g., the Arctic and deserts) limits our understanding of the natural dynamics of mortality in the species. We found that many individual, social and environmental variables determine mortality values, and our global perspective allowed us to disentangle long-standing debates in large carnivore ecology, including support for the hypothesis that human-caused and natural mortality are additive. Conclusion: Our review provides the baseline framework and a standardised global dataset to guide future research and policy-making on large carnivore conservation, emphasising the increased risk of mortality for wolves living alongside humans, an issue that may be particularly overlooked as populations expand.