Meeting Abstract
Blood levels of energy substrates can predict mass change and are often used as indicators of overall nutrition and health in birds. However, other factors such as sex, body mass, glucocorticoid-induced energy mobilization, and dietary intake may also influence circulating substrate concentrations. As more studies seek to connect avian condition or fitness to single measurements of energy substrates, understanding the factors that generate variation in these levels in wild animals is increasingly important. To this end, we conducted two experiments on free-living black-legged kittiwake (Rissa tridactyla) chicks. In the first experiment, we tested the hypothesis that energy substrate levels vary in response to long term-food availability. We compared plasma triglyceride levels of chicks from nests provided with long-term food supplementation to levels of age-matched chicks from unsupplemented nests. Chicks in nests without supplementation had significantly lower triglyceride levels than chicks in supplemented nests. In the second experiment, we hypothesized that recent food consumption has a stronger effect on levels of circulating energy substrates than acute fluctuations in glucocorticoid levels. An hour before experimentally elevating corticosterone in chicks, we recorded behavior at experimental and control nests to determine the time of the most recent feeding. We evaluated the relative contributions of time since feeding and corticosterone manipulation to plasma glucose, triglycerides, and cholesterol concentrations. If recent feeding and acute corticosterone elevation affect circulating levels of these metabolites, then they may not be accurate indicators of long-term nutritional status.
