Migratory orientation of sedge warblers (Acrocephalus schoenobaenus) in relation to eating and exploratory behaviour

Abstract

Orientation tests performed with Emlen funnels show much variation. This scatter in responses can be partially explained by considering the birds' personalities. We studied a Passerine migrant, the Sedge Warbler (Acrocephalus schoenobaenus), on autumn passage at Kalimok Biological Station, Bulgaria. Birds caught in the morning were kept in cages with known and regularly controlled amounts of food. In the evening they were tested for orientation, the next morning they were observed for 3 min in an unfamiliar cage, then released. Birds that ate on the first day oriented in the expected, southward direction, non-eating birds were scattered. Eating behaviour was related to the exploration pattern on the next day. Eating birds moved and flew less, hopped, looked around and explored the cage more, and were quicker in eating a food item if present. Lean birds ate and explored more but also oriented better, contrary to expectations where fat reserves indicate readiness for migration. A hypothesis is discussed where fat, migration and personality may be linked. Personality aspects may influence the individuals' ability to cope with an experimental situation and influence the outcome of the tests, therefore its analysis can help in predicting the birds' performance in apparently unrelated experiments.