Digestibility of prey by the White Stork (Ciconia ciconia) under experimental conditions

Abstract

Food composition of the White Stork Ciconia ciconia has been widely studied by pellet analysis throughout Europe, but the effect of digestibility on pellet contents has remained unclear. We studied the effect of digestion on the composition of pellets (N = 480) under experimental conditions in Poznañ Zoological Garden in 2004–2005. Twenty-four captive wild-born White Storks were fed mammals, birds, amphibians, fish, insects and earthworms. Only the remains of mammals, birds and insects were found in the regurgi-tated pellets. Bones were present in 13.1% of pellets. Three chosen osteological pellet components (skulls, mandibles and innominate bones) were analyzed to determine the amount of bone loss by digestion. The digestive efficiency was greater than 95%. Based on a literature review, we compared results of pellet analyses with methods not affected by digestion (direct observations and prey remains). The invertebrate : vertebrate ratio in the White Stork diet differed significantly between methods. Prey biomass rather than the number of prey items should be considered a better reflection of the diet.