Morbidity and mortality studies using data from wildlife rehabilitation facilities can be useful for understanding threats to free-ranging raptor populations. This study utilized medical and necropsy records of free-ranging sick and/or injured raptors presenting to the UC Davis Veterinary Medicine Teaching Hospital from 1995-2022 (n=3,840). A similar published study evaluating raptors at the same institution from 1983-1994 provides a unique opportunity to assess patterns in morbidity and mortality among raptors presenting to this hospital over a forty-year period. A supervised machine-learning approach was utilized to classify each case according to a diagnostic category from free text data entered into the fields of ‘presenting complaint,’ ‘physical exam findings,’ and ‘clinical diagnosis,’ in the raptors’ medical records. Diagnostic categories were entered manually from necropsy records. A time series analysis evaluated trends over time in numbers of raptor admissions and logistic regression models evaluated factors associated with increased odds of survival. Red-tailed hawks (Buteo jamaicensis), barn owls (Tyto alba), and great-horned owls (Bubo virginianus) were the most common species admitted to the hospital for clinical care. This dataset, compared to the previously published study, had comparatively fewer western screech owls (Megascops kennicottii) and American kestrels (Falco sparverius) while red-shouldered hawks (Buteo lineatus) and Cooper’s hawks (Accipiter cooperii) numbers were increased. The most common infectious diseases identified were Aspergillus spp., Chlamydia spp., West Nile virus (WNV), and Trichomonas spp. Overall, traumatic injury and infectious disease were the most common causes of morbidity and mortality in this study. No significant trends were detected in the numbers of cases presenting across our study period nor in the numbers of traumatic, infectious, and orphaned cases. Disease category, life stage, and season were significantly associated with survival. Birds with an infectious diagnosis had lower odds of survival while orphaned birds had higher odds of survival. Species, life stage, and season were significantly associated with infectious disease status. Summer, fall, and winter were associated with a higher odds of aspergillosis. Diurnal species also had higher odds of being diagnosed with aspergillus. Winter and spring seasons, diurnal species and sub-adult birds were all significantly associated with a chlamydia diagnosis. Summer, diurnal and adult life stage were significantly associated with WNV diagnosis. Nocturnal species was significantly associated with trichomoniasis diagnosis. The data compiled over this extensive forty-year period provides a valuable resource for understanding the causes and dynamics of morbidity and mortality in California raptor populations, which can be useful in informing wildlife conservation strategies and rehabilitation efforts.
