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

Environment, Behavior and Physiology: Do Birds Use Barometric Pressure to Predict Storms?

Severe storms can pose a grave challenge to the temperature and energy homeostasis of small endothermic vertebrates. Storms are accompanied by lower temperatures and wind, increasing metabolic expenditure, and can inhibit foraging, thereby limiting energy intake. To avoid these potential problems, most endotherms have mechanisms for offsetting the energetic risks posed by storms. One possibility is to use cues to predict oncoming storms and to alter physiology and behavior in ways that make survival more likely. Barometric pressure declines predictably before inclement weather, and several lines of evidence indicate that animals alter behavior based on changes in ambient pressure. Here we examined the effects of declining barometric pressure on physiology and behavior in the white-crowned sparrow, Zonotrichia leucophrys. Using field data from a long-term study, we first evaluated the relationship between barometric pressure, storms and stress physiology in free-living white-crowned sparrows. We then manipulated barometric pressure experimentally in the laboratory and determined how it affects activity, food intake, metabolic rates and stress physiology. The field data showed declining barometric pressure in the 12–24 h preceding snowstorms, but we found no relationship between barometric pressure and stress physiology. The laboratory study showed that declining barometric pressure stimulated food intake, but had no effect on metabolic rate or stress physiology. These data suggest that white-crowned sparrows can sense and respond to declining barometric pressure, and we propose that such an ability may be common in wild vertebrates, especially small ones for whom individual storms can be life-threatening events

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