Whereas changes in the behaviour of urban birds have been frequently documented - e.g. urban blackbirds are often tamer than their relatives from "natural" habitats - it was not previously known whether the physiological stress response also changes to suit the urban life style. If so, then it should be tested whether this adjustment is based on the flexibility of individuals experiencing different environmental conditions or is the result of micro-evolutionary adaptations that have evolved during the urbanisation process.
Scientists at the Max Planck Institute for Ornithology Andechs/Seewiesen in Germany, originally under the leadership of the late Max-Planck Director Dr. Eberhard Gwinner, answered these questions in a recent experiment. They hand-raised European blackbird nestlings collected from the centre of Munich, Germany and a nearby forest area (beeline distance 40 kilometres) and kept both groups in the same bird room for one year. These two groups therefore lived under exactly the same controlled environmental conditions, both during their developmental phase and later during the experiment.
During their first autumn, winter and spring, Jesko Partecke applied a standardised capture and handling stressor protocol to all urban and forest blackbirds and simultaneously collected blood samples, to determine the concentration of corticosterone, the stress hormone in birds. Under normal conditions, i.e. undisturbed, urban and forest blackbirds did not differ in their corticosterone secretion. In addition both groups showed a similar acute hormonal stress response during their first fall. This, however, changed considerably during their first winter and spring: Then the stress response of urban blackbirds was distinctly blunted in comparison to their forest counterparts.
"These results show, for the first time, that city life changes physiological
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Contact: Dr. Jesko Partecke
partecke@orn.mpg.de
49-815-237-3130
Max-Planck-Gesellschaft
1-Sep-2006