Length of stay in rehabilitation influences magnitude of the acute stress response in birds of prey

Wild animals are occasionally injured or become ill as a result of natural causesor human activity. As a way to remediate the damage imposed by humans onwildlife populations, these animals may be taken in for rehabilitation. Federallaws for rehabilitators set limits for the length of time a bird can remain inrehabilitation before a final decision on release or euthanasia is made. Little isknown about the consequences of longer stays in captivity within that limitedwindow with regard to stress physiology of the animals. The authors hypothesisedthat length of stay in rehabilitation would influence the ability of raptorsto mount a full stress response upon release from rehabilitation. Blood sampleswere taken from each bird upon admission for rehabilitation and immediatelyprior to their release, a process by which the animals are exposed to a significant,acute stressor of capture, handling, and examination. A blood samplewas collected for analysis of heterophil to lymphocyte ratios (H:L), whichare indicative of long-term baseline stress. The authors found that as length ofstay increased, the difference in corticosterone levels reached during an acutestressor from admission samples to release samples decreased. Baseline stress,as indicated by H:L, was not significantly affected by length of stay. The resultssuggest that birds of prey in rehabilitation habituate to captivity the longerthey stay in captivity and may lose some degree of natural responsiveness tostressors.