Raptor mortality in Ontario, Canada: retrospective summary (1992 - 2014) including the effects of West Nile Virus

Raptors are susceptible to anthropogenic causes of mortality, and as top predators, are vulnerable to dynamic environmental conditions that may affect habitat and prey availability. In addition, since 1999, many North American... [ view full abstract ]

Raptors are susceptible to anthropogenic causes of mortality, and as top predators, are vulnerable to dynamic environmental conditions that may affect habitat and prey availability. In addition, since 1999, many North American raptor species have proven susceptible to West Nile virus (WNV)-associated morbidity and mortality. We retrospectively evaluated postmortem diagnostic data from raptors submitted to the Ontario/Nunavut node of the Canadian Wildlife Health Cooperative from 1991 to 2014 (n=1,449). Submissions encompassed 29 species, the most common of which were the red-tailed hawk (Buteo jamaicensis; 21.3%; n=308) and great horned owl (Bubo virginianus; 16.4%; n=237). Trauma (49.4%; n=716), followed by emaciation (16.6%; n=241), accounted for the majority of deaths among all raptor species and was most commonly attributed to collisions (47.3%; n=339). High mortality rates resulting from emaciation may reflect the necessity of having a full complement of sensory and physical capabilities in order to feed. Using multivariable exact logistic regression, we assessed the impact of WNV on the proportion of carcass submissions diagnosed with infectious diseases and whether submissions with WNV varied by sex or age (mature vs. immature). The odds of being diagnosed with an infectious disease in all raptors and red-tailed hawks were significantly greater after the arrival of WNV to Ontario (2001) compared to the period before its arrival (all raptors: OR=1.47, 95% CI=1.07-2.04, p=0.0179; red-tailed hawks: OR=2.54, 95% CI=1.30-5.18, p=0.0049). Age and sex were not significantly associated with the odds of being diagnosed with WNV. Although limited by the biases of passive surveillance, these results suggest that human-associated deaths (e.g., due to trauma) and emaciation are relatively common among Ontario raptor carcasses submitted for diagnostic evaluation. In addition, the introduction of WNV to Ontario has significantly increased the proportional mortality of submissions related to infectious causes, and continued monitoring is warranted.