Energy storage dynamics in breeding Arctic seabirds

Abstract

This thesis describes investigations into the energy store (defined as the size of lipid stores) dynamics in breeding Arctic seabirds. The first chapter compares three species feeding at similar trophic levels but with different life history, physiological and foraging strategies, and breeding strategies. They managed their stores differently during poor environmental conditions. Though lipids were the primary tissue driving changes in body composition in Thick-billed Murres and Northern Fulmars, lean tissues were most dynamic in Black-legged Kittiwakes. Chapter two presents a method for evaluating the size of lipid stores non-lethally in Thick-billed Murres and Northern Fulmars using plasma fatty acid composition and concentration. Traditional (morphometric) tools had less predictive ability (especially for Thick-billed Murres) than plasma fatty acids. In Chapter three, I show that the plasma fatty acid signatures of Thick-billed Murres breeding at low and high Arctic colonies differ; likely an effect of differing diets. In addition, the concentration of plasma fatty acids increases during the breeding season, and is highest during chick-rearing. It is proposed that this may reflect a greater need for metabolic fuels as chick-rearing is likely the period of greatest energy expenditure. In Chapter four, the results of an egg replacement study are presented. Thick-billed Murres were made to lay a replacement egg following the removal of the first laid egg. The fatty acid signatures of the female and male plasma and of the first and replacement eggs were identified. Fatty acid signatures of eggs were highly conserved and those fatty acids found in the highest concentration in eggs were depleted in females after laying the replacement egg. In addition, from comparisons of the fatty acid signatures of eggs and potential prey species, I suggest that local sources of fatty acids could be utilised for the production of the replacement egg. In Chapter five, the way in which breeding adults manage an increase in the cost of diving is examined. In two experiments, conducted during two breeding seasons, the chick growth and plasma fatty acid concentrations of handicapped versus control adults were compared. Generally, adults passed on the increase in cost of diving to their chicks as chick mass gain was significantly less in some of the treatment groups. In addition, a feeding watch study suggests that this was because handicapped adults fed their chicks less frequently than control groups. This thesis represents the most physiologically intensive studies that have been conducted to date on wild breeding auks and is presented in the context of the potential effects of environmental change.