Excreted steroid metabolites in bird droppings: behavioural studies using baseline patterns and stimulus-specific responses

Hirschenhauser K.

Max Planck Institute for Ornithology, Seewiesen, Germany and Department of Behavioural Biology, Faculty of Life Sciences, University of Vienna, e-mail: khirschenhauser@orn.mpg.de

The physiological mechanisms underlying behaviour have been studied in birds since the early days of ethology. Measuring hormone metabolites non-invasively is popular with ethologists for a number of reasons. It does not require catching and handling of the birds, which may interfere with ongoing social interactions and measured hormone levels and thus allows repeated sampling.  I will emphasize avian studies, which have shown that behaviour may induce substantial hormone changes.  In geese, only watching another individual being caught increased circulating corticosterone levels of the spectators.  Measuring excreted steroid metabolites from bird droppings is advantageous for monitoring long-term patterns, as well as stimulus-specific responses.  We monitored the seasonal patterns of excreted androgen and glucocorticoid metabolites from a free-living flock of the long-term monogamous greylag geese (Anser anser) in Grünau.  The seasonal baseline patterns differed due to social status, e.g. between singletons, paired and parental geese.  Furthermore, the ‘within-pair testosterone compatibility’ (the degree of co-variation between the male and female pair partners’ seasonal androgen patterns) predicted the pair’s reproductive output.  In addition to seasonal variation, testosterone may increase in response to sexual or aggressive encounters.  Knowing the effective sampling time for dropping collection is essential for studies of stimulus-specific hormonal responses.  This may be fiddly with bird droppings because birds excrete urine and faeces jointly via the cloaca.  Details on steroid metabolism and excretion kinetics are known for the Japanese quail (Coturnix japonica).  We have used individual droppings for tests of the post-conflict testosterone changes in staged dyadic fights between male Japanese quails.  After fighting, male quail had changed levels of testosterone metabolite and the relationship between testosterone and dominance was considerably affected by social and contextual factors.  These data suggest that behavioural interactions, or a single encounter an individual has experienced, can induce hormone changes and vice versa, a single transient hormone surge may affect the individual’s future success.