Glucocorticoid physiology and behavior during life history transitions in Laysan Albatross (Phoebastria immutabilis)

Organisms have different life history stages where their energetic priorities differ between the goals of growth, survival, and reproduction. Behavioral decisions within stages and in the transition between stages have significant repercussions for future success so the timing of behaviors is extremely important. In this dissertation, I ask: How do intrinsic and extrinsic factors control the timing of behavioral decisions during tradeoffs within life history stages (the tradeoff between reproduction and self maintenance in breeding adults), and transitions between life history stages (the transition to independence in young animals) in a pelagic seabird, the Laysan Albatross (Phoebastria immutabilis). First, I ask how physiology changes during incubation fasts over the entire 2-month incubation period. I found total corticosterone (CORT) increased both within individual incubation shifts and over the season as body mass declined. Corticosteroid binding globulin (CBG) significantly increased as individual body condition declined. Though CORT secretion steadily increased during long, repeated fasts in this species, CBG may also rise to protect the reproductive attempt from the inhibitory effects of CORT on parental behavior. Next, I explore individual variation in parental provisioning trips during the chick rearing period. I found that surprisingly, adults expected to invest highly in their current reproductive effort, performed a pattern of foraging trips thought to be the strategy of adults investing in self-maintenance. This challenges previous work from the southern hemisphere and indicates that environmental differences in the northern hemisphere may change the distribution or predictability of ocean resources such that the benefit of different types of trips may not be fixed. Finally, I investigate morphology and physiology in chicks approaching fledging. I suggest that there are two primary factors contributing to the timing of fledging in Laysan Albatrosses: wing disc loading and plasma free CORT levels. After chicks reach a critical developmental threshold, they may fledge if food delivery is inadequate or stay if it is plentiful. When food delivery is unpredictable and chicks lose energetic stores, free CORT levels may fine-tune the timing of fledging: chicks with high free CORT when they reached the fledging threshold fledged sooner than chicks with low CORT levels