Determining Physiological Stress Levels of Rescued Birds by Measuring Feather Corticosterone in a Retrospective Study
Authors: Dudley Erin , Zhang Jingyi , Pahuja Harsh , Narayan Edward J 
Published: June 2024

Australia’s avian species are unique and diverse. Due to the dramatic changed in distribution, physiology, and behaviour caused by both changing climatic conditions and human activities, Australian bird species becomes highly vulnerable to health-related factors such as impact injury and vehicle trauma, as well as environmental-related stressors such as animal attack and abnormal behaviours. This is reflected in increasing number of avian patients received by wildlife hospitals. The most common outcome of avian species in wildlife hospitals was euthanasia, only few of them were released back into their ecosystem. During the process of bird rescue and rehabilitation, stress can be caused by various stressors such as injury, infection, trauma, shock and stressful environment in wildlife hospitals and rehabilitation centres. Therefore, in order to better understand the causes of the high rates of mortality and improve the management and conservation strategies, it is important to study the species responses to environmental changes. Similar with other species, in birds, the HPA axis plays an essential role in maintaining homeostasis by producing glucocorticoids (corticosterone in birds). In this study, we sampled a total of 30 individuals humanely euthanised at the Adelaide Koala and Wildlife Centre (AKWC), and noted their clinical information. Feather samples were collected from all 30 individuals, and then were processed and analysed for corticosterone levels using enzyme-immunoassay (EIA). The biological relevance of feather CORT assay was evaluated by comparing the absolute levels of CORT between birds. We also analysed the effects of different stressors by grouped the diagnosis into acute and chronic categories. Although results suggest that stress levels were variable between the diagnosis, no statistically significant difference was found between these two categories in this study due to the limited sample size. We also obtained patient records from the 2022-2023 period from AKWC for retrospective analysis. Records were categorized and analysed based on the diagnoses, species and admission dates. Retrospective analysis suggests that in 2022, the Rainbow Lorikeet had the highest admission rate (192/544, 35.29%), followed by Magpie (124/544, 22.79%). Most admissions occurred in Summer. Musculoskeletal injury was the most prevalent diagnosis across all species with Magpies having the highest rates (73.39%) across all diagnoses and Rainbow Lorikeets the second highest (36.46%). Beak and Feather disease (BFD) was another common diagnosis for lorikeets. Data collected at 2023 followed the similar trend. This is the first study that uses non-invasive method to determine stress levels of rescued Australian native avian species, aims at improving and implementing native avian species management and conservation initiatives. This research also provides a basis for future studies which allow for more detailed analyses of wild populations and a broader range of species.