DAILY TIME ALLOCATION AMONG ADULT AND IMMATURE YELLOW-EYED JUNCOS OVER THE BREEDING-SEASON

Daily time-budgets of adult and immature yellow-eyed juncos, Junco phaeonotus, were examined over the course of the breeding season to compare the relative severity of time constraints among breeding adults and between breeding adults and their offspring. No significant differences in time allocation between males and females were found at any stage of the breeding cycle. Adults feeding nestlings spent substantially more time foraging and flying than females engaged in incubation and the males paired to such females. The allocation of time to foraging peaked after the young left the nest and, among adults, parents caring for recently fledged young faced the most severe time constraints. The allocation of time to foraging and flying among dependent juncos gradually increased over the fledgling period. Of all the age classes and reproductive stages examined here, the recently independent juveniles faced the most severe time constraints, spending almost all of the daylight hours foraging. Older independent juneniles spent less time foraging and more time flying than recently independent juncos. The first few weeks of independence provides a strong opportunity for selection on the efficient allocation of time to competing activities among yellow-eyed juncos. © 1990.