Species differences in diet and the development of seed digestion in partridge chicks Perdix perdix and Alectoris rufa.
Chicks of both the Grey and the Red-legged Partridge feed on arthropods and plant material, mainly leaves and seeds. Fully grown partridges are mainly herbivorous and the proportion of plant material eaten increases rapidly during early life in both species, but plant material predominates in the diet of the Red-legged Partridge from an earlier age than for the Grey Partridge. Red-legged Partridge chicks are also able to disrupt grass seeds efficiently during passage through the digestive tract from an earlier age (2 days) than Grey Partridge chicks (10 days). It is suggested that the difference in timing between species in the development of herbivory is associated with this difference in digestive ability.
Recent studies of the feeding behaviour and diet of birds have revealed a profusion of subtle differences between closely related species, individuals and age groups. In some cases these differences are clearly correlated with differences in external morphology, as for example for inter- and intra-specific variation in seed size preference, handling ability and bill morphology in finches (Kear 1962, Grant et al. 1976). Developmental and species differences in the ability to process food in the digestive tract have received much less attention, though digestive constraints have been found to influence the selection of food in the Woodpigeon Columba palumbus (Kenward & Sibly 1977).
In this paper we show that the externally similar precocial chicks of two species of partridges (Galliformes: Phasianidae) eat different diets when foraging in the same habitat. We present evidence that this may be related to a difference in their ability to process seeds in the digestive tract.