The adrenocortical stress-response of Black-legged Kittiwake chicks in relation to dietary restrictions

In this study we examined hormonal responses of Black-legged Kittiwake (Ris sa tridactyla) chicks to experimental variations in energy content and nutr itional quality (low or high lipid to protein ratio, LPR) of their food. St arting at the age of 10 days, chicks were fed either high or low LPR fish a t 30, 50, 70 and 100% of ad libitum energy intake. After 20 days of treatme nt, chicks were exposed to a standardized acute handling and restraint stre ss protocol, where a baseline sample was taken immediately after taking a c hick from the nest, and three additional blood samples were taken at interv als up to 50 min. Testosterone and corticosterone titres in plasma were mea sured via radioimmunoassay. We found that baseline testosterone levels were not significantly affected by the experimental treatments. Food-restricted chicks had elevated baseline and acute stress-induced levels of corticoste rone compared to chicks fed ad libitum. An elevation of circulating levels of corticosterone in energetically stressed individuals was further magnifi ed by low nutritional quality of food. Baseline and acute stress-induced co rticosterone levels of chicks were negatively correlated with their fat res erves. We conclude that the physiological condition of Black-legged Kittiwa ke chicks can be assessed reliably by measuring circulating levels of corti costerone. We discuss short- and long-term effects of elevated corticostero ne secretion in food-stressed nest-bound chicks.