Foraging behavior predicts age at independence in juvenile Eurasian dippers (Cinclus cinclus)

Abstract

Timing of foraging independence may be controlled by parents, offspring, or both and may have consequences for dispersal, reproduction, and survival. In a study of juvenile Eurasian dippers (Cinclus cinclus), I examined the relationship between individual differences in parental provisioning, the development of foraging, and the timing of independence. Young dippers forage very differently from adults, specializing on small, stationary prey, such as simuliid larvae (Diptera), and avoiding energetically costly and highly skilled foraging techniques, such as diving, by which adults obtain larger prey. In my Welsh study area, age at independence varied substantially within and between broods. Juveniles that relied more on simuliids and less on larger prey were independent sooner, as were juveniles with higher rates of intake while foraging; the effect was obvious 3-4 days after fledging. Provisioning rate and total caloric intake over the dependent period was unrelated to age at independence, although greater reliance on parental feeding was associated with higher total caloric intake. Higher rates of intake from begging were correlated with reduced foraging time. The results demonstrate that the acquisition of the adult foraging strategy is not a prerequisite for independence or, hence, dispersal. In fact, mastering the skills necessary to capture larger prey may delay independence. Individual juvenile dippers seem to find different solutions to the trade-off between gaining sufficient food (either from begging or from foraging for simuliids) and the eventual necessity of learning to forage like an adult.