ABSTRACT
BACKGROUND: Hummingbirds are frequently presented to California wildlife rehabilitation centers for medical care, accounting for approximately 5% of overall admissions. Age, sex, and reason for admission could impact hummingbird survivability, therefore identification of these factors could help maximize rehabilitation efforts. METHODS: Mixed-effects logistic regression models were used to identify specific threats to the survival of 6908 hummingbirds (1645 nestlings and 5263 non-nestlings) consisting of five species (Calypte anna, Calypte costa, Selasphorus rufus, Selasphorus sasin, Archilochus alexandri), found in urban settings, and admitted to California wildlife rehabilitation centers over 26 years. RESULTS: In total, 36% of birds survived and were transferred to flight cage facilities for further rehabilitation and/or release. Nestlings were more likely to be transferred and/or released compared to adult hummingbirds. After accounting for age, birds rescued in spring and summer were twice as likely to be released compared to birds rescued in the fall. A high number of nestlings were presented to the rehabilitation centers during spring, which coincides with the nesting season for hummingbirds in California, with the lowest number of nestlings presented in fall. Reasons for presentation to rehabilitation centers included several anthropogenic factors such as window collisions (9.6%) and interactions with domesticated animals (12.9%). Survival odds were lower if a hummingbird was rescued in a "torpor-like state" and were higher if rescued for "nest-related" reasons. Evaluation of treatment regimens administered at wildlife rehabilitation centers identified supportive care, including providing commercial nutrient-rich nectar plus solution, to significantly increase hummingbird survivability. DISCUSSION: Our results provide evidence of threats to hummingbirds in urban habitats, based on reasons for rescue and presentation to rehabilitation centers. Reasons for hummingbird admissions to three California wildlife rehabilitation centers were anthropogenic in nature (i.e., being associated with domestic animals, window collisions, and found inside a man-made structure) and constituted 25% of total admissions. There was a clear indication that supportive care, such as feeding a commercial nectar solution, and medical treatment significantly increased the odds of survival for rescued hummingbirds.
ABSTRACT
A histopathologic study of free-ranging hummingbirds found in California, US was performed to identify mortality trends. Tissues from 61 wild hummingbirds representing five native California species collected by the San Diego Zoo from 1996 to 2016 or the Lindsay Wildlife Experience from 2015 to 2017 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 excluded from this study. Lesions were sorted by organ, etiology, and gender. The most commonly affected organs were the lung (68%, 40/59), followed by the ingluvies (67%, 34/51) and the liver (54%, 33/61). While some birds had minimal or nonspecific lesions, 23% (14/61) had lesions primarily attributable to trauma, 16% (10/61) had lesions associated with bacteria, fungi, or viruses, 11% (7/61) had parasitic lesions, and 13% (8/61) had multifactorial concurrent processes. Infectious disease lesions included those associated with avian poxvirus, intestinal adenovirus, disseminated aspergillosis, bacterial septicemia, malaria ( Haemoproteus spp.), and mycobacteriosis. The most commonly identified parasitic infection was intestinal cestodiasis, for which there was no significant associated intestinal damage, although the large size of these cestodes may have affected digestion. The incidence of traumatic lesions did not vary significantly by sex, age, species, or sampling location. Other significant findings not related to disease or trauma, but not previously documented, were histologic evidence of a gallbladder and the presence of aortic ossification. Our study reported mortality trends at a population level for free-ranging hummingbirds found in California and identified the presence of intestinal adenovirus and two anatomic structures not previously described.
