SEABURY SPRAGUE, R.**; BREUNER, C.W.; University of Texas at Austin; University of Texas at Austin: Timing of fledging, body condition, and corticosteroid binding globulin in Laysan Albatross

Fledging is a major life transition for birds, moving from the safety of a nest into an environment where they must find food and avoid predators. Timing of fledging can have significant effects on future survival and breeding success. Previous studies in several species have shown elevated plasma corticosterone (CORT) in the days before fledging, though the reason for this increase is not clear. Laysan Albatross Phoebastria immutabilis chicks have an extended post-hatching period of 165 days where they peak at a mass of 1 � times the weight of an adult. However, as they approach fledging, chicks fast for days to weeks between feedings and drop significantly in mass while still putting energy into feather growth. We are currently investigating the interaction of several physiological and morphological factors influencing fledging. Initial results show that CORT increases as chicks approach fledging. Additionally, corticosteroid binding globulin (CBG) declines significantly before fledging. We found that binding protein levels are positively correlated with body condition � as chicks fast longer and lose weight, their CBG levels fall. To test this relationship, we supplementally fed chicks for four weeks before fledging. Fed birds did not decrease in body condition, did not have the correlated decrease in CBG, and delayed fledging for an average of 9 days. Our study suggests that deteriorating body condition in fasting albatross chicks causes a decrease in CBG which, paired with an increase in CORT and a suitable level of wing development, prompts the chicks to fledge.