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First published online August 28, 2009
Journal of Experimental Biology 212, 2902-2907 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.033332
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Information from the geomagnetic field triggers a reduced adrenocortical response in a migratory bird

Ian Henshaw1, Thord Fransson2, Sven Jakobsson1, Susanne Jenni-Eiermann3 and Cecilia Kullberg1,*

1 Department of Zoology, Stockholm University, SE-106 91 Stockholm, Sweden
2 Swedish Museum of Natural History, Bird Ringing Centre, Box 50 007, SE-104 05 Stockholm, Sweden
3 Swiss Ornithological Institute, CH-6204 Sempach, Switzerland

* Author for correspondence (cecilia.kullberg{at}zoologi.su.se)

Accepted 18 June 2009

Long-distance migrants regularly pass ecological barriers, like the Sahara desert, where extensive fuel loads are necessary for a successful crossing. A central question is how inexperienced migrants know when to put on extensive fuel loads. Beside the endogenous rhythm, external cues have been suggested to be important. Geomagnetic information has been shown to trigger changes in foraging behaviour and fuel deposition rate in migratory birds. The underlying mechanism for these adjustments, however, is not well understood. As the glucocorticoid hormone corticosterone is known to correlate with behaviour and physiology related to energy regulation in birds, we here investigated the effect of geomagnetic cues on circulating corticosterone levels in a long-distance migrant. Just as in earlier studies, juvenile thrush nightingales (Luscinia luscinia) caught during autumn migration and exposed to the simulated geomagnetic field of northern Egypt increased food intake and attained higher fuel loads than control birds experiencing the ambient magnetic field of southeast Sweden. Our results further show that experimental birds faced a reduced adrenocortical response compared with control birds, thus for the first time implying that geomagnetic cues trigger changes in hormonal secretion enabling appropriate behaviour along the migratory route.

Key words: bird migration, fuelling decisions, hormones, corticosterone, geomagnetic cues


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