Causes of mortality in North American populations of large and medium-sized mammals

The proportion of different causes of death (cause-specific mortality) is an important indicator of local ecology and local selective forces shaping behavioral and morphological adaptations and can easily be compared between species. These mortality causes are best measured by remotely monitoring individuals with radio transmitter tags to detect their eventual demise and conducting postmortem examinations to determine the exact cause of death. Although studies of mortality causes have been conducted for many mammal species, there has been no attempt to examine trends across species. Here, we review data from 69 North American mammal populations across 27 species of mostly large and medium sized mammal species, summarizing 2209 total mortality events, 1874 of which were known causes. Of the known causes, humans are the main cause of mortality (51.8%), followed by natural (48.5%). Among natural causes, predation (35.2% of known) was most prevalent in smaller species, especially herbivores. Anthropogenic causes were higher for legally unprotected populations, especially carnivores and larger species. Hunting (35.3% of known) was the most important source of human-caused mortality followed by vehicle collision (9.2% of known), which was positively correlated with the degree of human development of the local landscape. Protected populations had a 44% lower level of human-caused mortality, although it was still an important component of their overall mortality (34.6%). Our results show the variety and pervasiveness of anthropogenic mortality on many mammal species, suggesting that humans cause most mortalities observed in larger mammals in North America. These anthropogenic mortalities may represent strong selective forces for animal populations and offer mechanistic support for the growing body of evidence for rapid evolutionary shifts in behavior and morphology in response to human caused changes to the landscape.