An experimental examination of interindividual variation in feather corticosterone content in the House Sparrow, Passer domesticus in southeast Australia

Non-invasive techniques for measuring glucocorticoids (GCs) have become more prevalent, due to the advantage of eliminating the effects of animal disturbance on GC levels and their potential to provide an integrated, historic estimate of circulating GC levels. In the case of birds, corticosterone (CORT) is deposited in feathers, and may reflect a bird's GC status over the period of feather synthesis. This technique thus permits a retrospective view of the average circulating GC levels during the moult period. While it is generally assumed that differences in feather CORT content (CORTf) between individuals reflects their different stress histories during either natural or induced moult, it is not clear how much of this variation is due to extrinsic versus intrinsic factors. We examined this question by determining CORTf in free-living house sparrows (Passer domesticus) from two populations, one urban and the other rural, that were plucked before and after exposure to different plasma CORT levels while held captive. We experimentally manipulated plasma CORT by implanting birds with either a corticosterone-filled, metyrapone-filled, or empty ('sham') silastic capsule as replacement feathers first emerged. The pattern of post-treatment CORTf was consistent with our expectations, based on plasma CORT levels of an experimentally implanted reference group. However, there was no statistically significant difference in CORTf between these treatment groups unless sex, population origin, and CORTf of original feathers for each individual were included in a model. Thus, birds with higher CORTf in feathers removed for this experiment tended to have higher CORTf in post-treatment replacement feathers, irrespective of treatment. In addition, we found that feather fault bar scores were significantly higher in CORT-treated birds than in the other two treatment groups, but did not vary directly with CORTf level. Our study therefore broadly confirms the use of feathers as a non-invasive tool to estimate plasma CORT during moult in birds, but importantly demonstrates the potential for intrinsic differences in stress characteristics between populations and individuals to obscure the effects extrinsic stressors might have on CORTf .

AvianBuffer: an interactive tool for characterising and managing wildlife fear responses

The characterisation and management of deleterious processes affecting wildlife are ideally based on sound scientific information. However, relevant information is often absent, or difficult to access or contextualise for specific management purposes. We describe 'AvianBuffer', an interactive online tool enabling the estimation of distances at which Australian birds respond fearfully to humans. Users can input species assemblages and determine a 'separation distance' above which the assemblage is predicted to not flee humans. They can also nominate the diversity they wish to minimise disturbance to, or a specific separation distance to obtain an estimate of the diversity that will remain undisturbed. The dataset is based upon flight-initiation distances (FIDs) from 251 Australian bird species (n = 9190 FIDs) and a range of human-associated stimuli. The tool will be of interest to a wide audience including conservation managers, pest managers, policy makers, land-use planners, education and public outreach officers, animal welfare proponents and wildlife ecologists. We discuss possible applications of the data, including the construction of buffers, development of codes of conduct, environmental impact assessments and public outreach. This tool will help balance the growing need for biodiversity conservation in areas where humans can experience nature. The online resource will be expanded in future iterations to include an international database of FIDs of both avian and non-avian species.