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

Abstract

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 humancaused 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.

Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park

“…Attempts to assess responses of organisms to emerging threats (e.g., invasive species, disease, climate change) often are hampered by lack of historical or baseline abundance data (41). We were fortunate to have available effort-corrected data from 1996-1997 comparable to the data on mammal relative abundances we have collected since the proliferation of pythons, allowing us to document declines in numerous mammal species accurately.…”

Terrestrial animal tracking as an eye on life and planet

“…Tracking studies have a long history of identifying factors related to animal survival and are the primary way to identify the time, location, and cause of death. A review of mortality in large and medium-sized North American mammals, including over 2000 animals tracked until their death, highlighted the importance of humans (i.e., hunters and cars), which accounted for 52% of mortalities, compared to 35% that fell prey to natural predators (45). Satellite technology allows us to monitor mortality of long-distance migrants, which has recently been shown to be much higher during migration (46).…”

Effect of paved road density on abundance of white-tailed deer

“…Similarly, a positive effect of road density on deer abundance could result from reduced predation by humans (hunting) in areas with higher road densities. In their review of causes of mortality of medium and large-sized mammals of North America, Collins and Kays (2011) found that while the probability of an animal-vehicle collision increases with increasing human footprint in the landscape, the rate of hunting decreases over the same gradient. Even if actual predation pressure is not substantially reduced in landscapes with high road densities, deer may be able to detect the presence of predators (the 'landscape of fear' concept: Hebblewhite and Merrill 2009;Manning et al 2009;Laundré et al 2010).…”