Differences between sexes in digestive efficiency of the white stork Ciconia ciconia under experimental conditions

Sex differences in digestive performance may be related to food contents, to body size as well as many other physiological traits. However, evidence for sex differences in the digestion of birds, especially in the case of predators, is scarce. Therefore we studied digestive efficiency, and also body size, intestine length and food selection of the wild white stork (Ciconia ciconia), under experimental conditions in the Poznań Zoo. Altogether 29 individuals of this species were investigated (9 males, 20 females). During 5-day- long experimental cycles, the diet of the birds consisted of mammals, birds, fishes and insects. The mean daily wet food intake (weight of the food eaten) during the experiment was 272.8g +/- 89.3 g for males and 342.7g +/- 157.4 g for females, but the difference between sexes was not significant (P = 0.226). The mean digestive efficiency showed a significant difference, i.e. in male white storks it amounted to 70.87% +/- 14.43%, whereas in females this value was 77.53% +/- 3.99% (P = 0.049). Digestive efficiency was slightly influenced by changes in body weight of storks during the experiment. Correlation coefficients between sexes also differed significantly (P = 0.037). The study showed that the digestive efficiency is positively correlated with the quantity of food intake and body weight.