Patterns of winter field use by Starlings Sturnus vulgaris: how important is prey depletion?

From a knowledge of Ideal Free Distribution theory(1) we might be able to p redict temporal patterns of habitat use by Starlings Sturnus vulgaris on th e basis of changes in resource availability. We measured depletion of soil invertebrates by Starlings by studying the foraging behaviour of individual Starlings held in enclosures. After one hour of foraging by these captive birds, there was a significant decline in the availability of prey. To inve stigate whether such prey depletion may influence the movements of wild bir ds between feeding areas we conducted all-day observations of an overwinter ing flock in the same habitat. Departure of Starlings fi om feeding areas c ould not be predicted on the basis of previous residence times in those are as, and there was no correlation between field residence times and subseque nt return times. However the flock was more likely to move to a nearby site when moving between feeding areas. We suggest that the level of foraging p ressure created experimentally exceeded that likely to occur in a natural s ituation. Although Starlings may attempt to use fields according to habitat quality, as measured by food availability, their patterns of habitat use c annot be predicted on this basis.