Non-invasive corticosterone treatment changes foraging intensity in red-eyed vireos Vireo olivaceus
Corticosterone is thought to play an important role in food caching and foraging behaviour. However, the direct influence of increased plasma corticosterone on feeding behaviour is still unclear. In this study the effect of increased corticosterone on feeding behaviour in migratory active red-eyed vireos Vireo olivaceus was investigated. We hypothesized that if increased corticosterone levels facilitate foraging behaviour, an increased number of visits to the food bowl by corticosterone treated birds would be seen. In addition to ad lib food during the experiment, the vireos were fed every full hour between 09.00-13.00 h with one meal worm injected either with 4 mu g corticosterone dissolved in 20 mu l DMSO, or with DMSO only as a control treatment. The presence or absence of a bird in the food bowl was recorded by a motion detector between 09.00-15.00 h. The non-invasive corticosterone treatment increased plasma corticosterone levels and caused vireos to visit the food bowl more frequently compared to control treated individuals between 11.00-12.00 h and 13.00-15.00 h. Our data indicate that corticosterone has an effect on feeding behaviour in birds.