Competition for food in urban pigeons: The cost of being juvenile

Abstract

The general-stated view that high mortality rates in young birds arises from a lack of behavioral proficiency is based on limited empirical evidence. The relationship between competitive foraging ability and age-specific mortality was examined in a free-ranging Rock Dove (Columba livia) population. In this system, competition for food was intense and predators were scarce. Young and adult pigeons showed considerable niche overlap, were members in the same flocks, and used similar foraging techniques, all of which favored competition between these age groups. Competition was especially intense when pigeons foraged on food provided by the public, which was the preferred and major food source for the population. Young pigeons were poorer competitors than adults in all situations analyzed. First, juveniles foraged less rapidly, and so were more vulnerable to exploitation competition. Second, juveniles were subordinate to adults within a despotic social system, and so suffered more from contest competition. These findings suggest that juveniles were less likely to attain a positive energy balance through the day and were more vulnerable to starvation and disease. As predicted, more juvenile corpses than expected were found during the study, indicating that young pigeons experienced higher mortality rates than adults. It is therefore suggested that differential mortality of juvenile and adult pigeons could in part arise from differences in competitive abilities over food.