USE OF ICE-SCOURED DEPRESSIONS BY MARSH-FORAGING SNOW GEESE (CHEN CAERULESCENS ATLANTICA)

We describe the foraging behaviour of staging greater snow geese (Chen caerulescens atlantica) as they feed in depressions caused by ice scouring in tidal marshes along the St. Lawrence River. We compared feeding success during the fall and spring staging season as the birds extracted rhizomes of Scirpus americanus. In these marshes, every growth cycle (summer) is followed by two distinct episodes of intensive exploitation by geese (fall and the following spring). Two kinds of foraging bouts were considered: (1) successful (i.e, with one or more ingestions) and (2) unsuccessful (i.e, without any ingestion). Geese sampled fewer depressions in the fall than in the spring because the proportion of depressions sampled with success was greatest in this season. Geese spent less time per depression in the spring, whether they were successful or not, but sampled more depressions instead. There was a decrease in the number of depressions sampled over the spring period. It is concluded that geese adjust their use of ice-scoured depressions to both inter- and intra-seasonal food availability (depletion). Behavioural mechanisms they might use to do so are discussed.