Ontogeny of Time Budgets in Yellow‐eyed Juncos: Adaptation to Ecological Constaints

Abstract

Observational studies showed that among fledgling Yellow—eyed Juncos (Juncos phaeonotus) rates of scanning for predators, pecking rates, and feeding rates increased dramatically with age and converged on adult rates as the young reached independence. Juveniles adjusted their vigilance level in response to their social situation, maintaining higher vigilance in flocks of juveniles than when foraging with their parents. Independent juveniles spent a larger proportion of their time foraging, thus spent more time exposed to predators, and had lower survivorship than adults. Independent juveniles appeared to have difficulty in acquiring sufficient food when foraging time was limited by severe weather. Young juncos foraging in juvenile flocks spent less time on vigilance and pecked more often than juveniles foraging along. Social foraging by juveniles increased the probability of surviving after parental care was terminated.