© Markus Jenny
Stress hormone levels in reintroduced grey partridges
Do human activities disturb the grey partridge and lead to chronic stress? If the reintroduction project in Switzerland is to be successful, it is essential to know more about the quality of the grey partridge’s habitat in relation to stress levels.
In Switzerland the grey partridge (Perdix perdix) was nearly extinct. Only in two areas, the Klettgau and the Champagne genevoise, a few individuals were left. The main reason for the dramatic population decline is the loss of habitat and – most probably - disturbance by human activities (pedestrians, dogs, joggers, bikers, agricultural activities). Human activities have an immediate effect on behaviour and evoke - on a long-term basis – a different use of the habitat. Moreover, the breeding success in the Klettgau was affected by big events of dog-sport during the breeding season. The Swiss Ornithological Institute started a reintroduction project in 1998 in the Klettgau and in 2004 in the Champagne genevoise. However, the question remained whether human activities evoke chronic stress in the grey partridges. To investigate this question we analysed the metabolites of the stress hormone corticosterone in the droppings of the birds. The same method was already successfully applied in the capercaillie (Thiel et al 2005) and the black grouse (Baltic et al 2005).
Droppings of grey partridges in two Swiss habitats and – for comparison - in less disturbed areas in Poland and Germany were collected and analysed. The method was validated in the master thesis by Cornelia Keiser. The field study was performed by the master student Benjamin Homberger.
We succeeded to set up an assay for the analysis of corticosterone metabolites. Preliminary experiments showed that ambient temperature and humidity influence the metabolite concentration. Therefore the droppings had to be collected as fresh as possible. The field study showed that the grey partridges were mainly in areas frequented by few people and that nearly no samples could be collected in highly frequented areas. This made the comparison between highly disturbed versus not-disturbed impossible within Switzerland. The comparison between samples collected in Switzerland and those from undisturbed areas in Poland and Germany did not reveal any significant difference. Also the raptors avoided areas highly frequented by humans. Apparently both species were forced into the same less disturbed habitat. The presence of the raptors however raised the corticosterone metabolite level. The metabolite level was also influenced by season and group size. During the breeding season the corticosterone metabolites levels are – as reported for other bird species - higher than outside the breeding season. It is hypothesized that corticosterone increases during life-cycle stages of increased demands to supply the organism with sufficient energy. Birds in groups have significantly lower corticosterone metabolite concentrations than single birds. This result confirms the hypothesis that life in groups is advantageous to avoid predators.
Prof. Dr. Rupert Palme, University of Veterinary Medicine Vienna