Successful homing of magnet-carrying white-chinned petrels released in the open sea

During the incubation period, white-chinned petrels, Procellaria aequinoctialis, repeatedly make foraging trips of several thousand kilometres in the open ocean from their small isolated breeding island. To test whether these birds rely on geomagnetic information to home, we displaced five individuals and released them in the open sea 300-360 km from home. They were prevented both from using route-based information during the passive displacement from the breeding island to the release site, and from using the geomagnetic field at the release site and on their way home (by carrying a mobile magnet on the head). They were equipped with satellite transmitters to record their homing movements. The five petrels homed efficiently (in 17-32 h) along paths that were on average slightly less than twice the homing distance. This showed that, at least when within a few hundred kilometres of home, white-chinned petrels are able to home successfully by relying only on nongeomagnetic site-dependent information. (C) 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.