Age-Related Differences in Ruddy Turnstone Foraging and Aggressive Behavior

Abstract

The foraging behavior of fall migrant Ruddy Turnstones was studied on the Massachusetts coast on 2 different substrates, barnacle-covered rocks and sand and weed-littered flats. Foraging rates differed significantly between the 2 substrates. On each substrate the foraging and success rates of adults and juveniles differed significantly while the frequencies of success were similar for both age-classes. The observed differences in foraging rates of adults and juveniles may be due to the degree of refinement of foraging techniques. Experience in searching for and handling prey may be a primary factor accounting for these differences, and foraging performance probably improves with age and experience. Alternatively, the differences may be due to the presence of inefficient juveniles that do not survive to adulthood.Both adults and juveniles in the tail-depressed posture were dominant in aggressive interactions much more frequently than birds in the tail-level posture. In mixed flocks of foraging adult and juvenile turnstones, the four possible types of aggressive interactions occurred nonrandomly. Adult over juvenile interactions occurred more frequently than expected, and juvenile over adult interactions were never seen. A tentative explanation of this phenomenon may be that juveniles misinterpret or respond ambivalently to messages conveyed behaviorally by adults and thus become especially vulnerable to aggression by adults. The transiency of migrants made it unfeasible to evaluate the persistence of this nonrandom aggression.