Corticosterone is not correlated with nest departure in snowy owl chicks (Nyctea scandiaca)

Snowy owl chicks typically depart from nests at approximately 18 days of age, but 3 weeks before taking their first flight. High concentrations of corticosterone have been implicated in behavioral changes in many species, leading us to assess corticosterone’s role in chick nest departure. Corticosterone titers in free-living chicks, however, do not predict this departure event. Baseline corticosterone concentrations decrease as chicks age. By 13 days, corticosterone concentrations are 50% of concentrations in 1-day-old chicks. Baseline concentrations, however, do not differ between departed and nest-bound chicks. Furthermore, corticosterone concentrations become significantly elevated 30 min after collecting the baseline sample, indicating that chicks are able to mount a corticosterone response to handling. This stress-induced rise in corticosterone also did not differ between departed and nest-bound chicks. Brood sizes varied, possibly resulting in increased stress in chicks from larger broods. Although many chicks died before reaching departure age, brood sizes at time of nest departure ranged from 1 to 10 chicks. Brood size was not correlated with age of nest departure or individual corticosterone concentrations. These data indicate that it is unlikely that corticosterone plays a role in triggering nest departure in snowy owl chicks.