Abstract

A retrospective histopathologic study of free-ranging hummingbird mortality in California was performed to identify mortality trends. Tissues from 57 wild hummingbirds representing five different native California species collected by the San Diego Zoo between the years of 1996–2016 or the Lindsay Wildlife Experience in 2015 and 2016 were histologically examined. Birds were either found dead or moribund at the time of submission or were euthanized due to unresolvable health issues. Long-term rehabilitated birds were not included in this study. Identified lesions were categorized by organ system and sex. The most commonly affected organ systems were the lung (67.3%), followed by the ingluvies (64.6%), and the liver (56.1%). While some birds had minimal or nonspecific lesions, a large proportion had lesions primarily attributable to trauma (22.8%); 14% had lesions associated with bacteria, fungus, or viruses; 12.3% had parasitic lesions; and 12.3% had multifactorial concurrent processes. Lesions of infectious disease included those associated with avian poxvirus, intestinal adenovirus, disseminated aspergillosis, bacterial septicemia, malaria (Haemoproteus spp.), and mycobacteriosis. The most commonly identified parasitic infestation was intestinal cestodiasis, for which there did not appear to be any significant associated intestinal pathology, though the large size of these cestodes may have impacted digestion. There was no apparent sex predilection for any of the identified lesions or processes.

Acknowledgments

The authors would like to thank the Wildlife Disease Laboratories at the San Diego Zoo and the Lindsay Wildlife Experience for providing hummingbird necropsy cases for review.