Diet and prey type selection by adult and young Blue Tits Parus caeruleus: the effect of correcting for prey digestibility.

Full article

Published:

Volume 41(2), December 1994. Pages 151-159.

Language:

English

Keywords:

Blue Tit, Parus caeruleus, correction factors, diet, differential prey digestibility, prey selection.

Abstract:

Diet composition and prey selection by adult and young, recently fledged blue tits Parus caeruleus, were analyzed by means of faecal sampling and measurements of prey availability in an area of holm oak pastoral woodland (Spanish dehesa) during July 1993. Correction factors for the digestibility of prey types were obtained by computing the number of recognizable prey items which appeared in the faeces of four captive adult blue tits fed with a mixture of intact individuals of five prey types. Comparisons of corrected and uncorrected estimates of diet composition suggest a serious underestimation of soft-bodied prey such as spiders and aphids in previous studies on Blue Tit diets. Corrected estimates showed that spiders were the most important prey in both adult and young birds' diets, followed by beetles and bugs (young birds) or aphids and larvae (adults). Selectivity of prey types was not much altered by the digestibility effect. Both age classes selected prey types on the basis of their energy content per gram of dry mass. These results were consistent with predictions from optimal diet models, bearing in mind that the small mean size of the prey types available would have implied small and similar handling times for all of them.