No abstract

Release of corticosterone in hungry kittiwake chicks facilitates begging and allows them to restore depleted energy reserves by increasing parental food provisioning. However, in order to avoid detrimental effects of chronic elevation of corticosterone, chicks might suppress adrenocortical activity in response to prolonged food shortages. In this study we examined temporal dynamics of corticosterone release in red-legged kittiwake (Rissa brevirostris) chicks exposed to prolonged restrictions in energy content and/or nutritional quality (low versus high lipid content) of their food. Starting at the age of 15 days, chicks were fed either high- or low-lipid fish at 40%, 65%, and 100% of ad libitum energy intake. Body mass measurements and baseline plasma samples were taken on a weekly basis after beginning of the treatment. After 3 weeks of treatment, chicks were exposed to a standardized acute handling and restraint stress protocol, where in addition to a baseline sample, three plasma samples were taken at intervals up to 50 min. We found that food-restricted chicks had lower body mass, chronically (during 2-3 weeks) elevated baseline and higher acute stress-induced levels of corticosterone compared to chicks fed ad libitum. Low lipid content of food further exacerbated these effects. An increase in baseline levels of corticosterone was observed within a week after energy requirements of food-restricted chicks exceeded their daily energy intake. A tendency for suppression of adrenocortical activity was observed in treatments fed low-lipid diets only at the end of the experiment. We suggest that nest-bound chicks, if food-stressed, might suffer deleterious effects of chronic elevation of corticosterone.

Summary1. Life-history theory predicts a trade-off between costs of current reproduction and future survival of individuals. Studies of short-lived animals in general support this prediction. However, the effect of nutritional stress during reproduction on survival of long-lived animals is poorly understood. 2. We examined the link between nutritional stress, fecundity and return to a breeding colony (hereafter 'survival') of black-legged kittiwakes (Rissa tridactyla) at two colonies with contrasting patterns in adult survival, fecundity, and numerical trends. 3. We tested the observational (at Duck and Gull Is., Cook Inlet, Northern Gulf of Alaska) and experimental (at Middleton I., Gulf of Alaska) relationships between variations in the secretion of the stress hormone corticosterone (CORT) and food abundance. Then, we examined the relationships between nutritional stress (as reflected in CORT), reproduction, and survival of individuals. 4. On average, CORT was higher in kittiwakes breeding on Duck I. (declining, low fecundity, high survival) compared to those breeding on Gull I. (increasing, high fecundity, low survival). 5. At both colonies, CORT was directly negatively correlated with food abundance quantified at sea. Experimental feeding of individuals ad libitum resulted in a reduction of CORT in birds breeding on Middleton I. These results suggest that CORT is a reliable measure of food availability and defines nutritional stress (stress) in kittiwakes. 6. On Gull I., where survival is low (86%), production of young declined as stress increased. On Duck I., where survival is high (93%), parents always failed in raising young, though they experienced a wide range of stress levels. 7. Survival of individuals is linked to their CORT levels during reproduction. High levels of CORT predicted disappearance of individuals from both colonies. 8. The results support the hypothesis that nutritional stress during reproduction affects both survival and reproduction in long-lived animals. However, even within a species the ways in which survival and reproduction trade-off against each other may vary among populations. Results suggest that reproductive consequences of nutritional stress might differ between declining and increasing populations, which should be tested. We conclude that severity of nutritional stress during reproduction is one of the major factors defining population processes in kittiwakes.

A climatic regime shift during the mid-1970s in the North Pacific resulted in decreased availability of lipidrich fish to seabirds and was followed by a dramatic decline in number of kittiwakes breeding on the Pribilof Islands. Although production of chicks in the mid-1970s was adequate to sustain kittiwake populations in the early 1980s, the disappearance of birds from breeding colonies apparently exceeded recruitment. No mechanism has been proposed to explain why recruitment would differ among fledglings fed lipid-rich or lipid-poor fish during development. Here we show that diets low in lipids induce nutritional stress and impair cognitive abilities in young red-legged kittiwakes, Rissa brevirostris. Specifically, growth retardation, increased secretion of stress hormones and inferior ability to associate food distribution with visual cues were observed in individuals fed lipid-poor diets. We conclude that lipidpoor diets during development affect the quality of young seabirds, which is likely to result in their increased mortality and low recruitment.

Early-life conditions can drive ageing patterns and life history strategies throughout the lifespan. Certain social, genetic and nutritional developmental conditions are more likely to produce high-quality offspring: those with good likelihood of recruitment and productivity. Here, we call such conditions "favoured states" and explore their relationship with physiological variables during development in a long-lived seabird, the black-legged kittiwake (Rissa tridactyla). Two favoured states were experimentally generated by manipulation of food availability and brood size, while hatching order and sex were also explored as naturally generating favoured states. Thus, the favoured states we explored were high food availability, lower levels of sibling competition, hatching first and male sex. We tested the effects of favoured developmental conditions on growth, stress, telomere length (a molecular marker associated with lifespan) and nestling survival. Generation of favoured states through manipulation of both the nutritional and social environments furthered our understanding of their relative contributions to development and phenotype: increased food availability led to larger body size, reduced stress and higher antioxidant status, while lower sibling competition (social environment) led to lower telomere loss and longer telomere lengths in fledglings. Telomere length predicted nestling survival, and wing growth was also positively correlated with telomere length, supporting the idea that telomeres may indicate individual quality, mediated by favoured states.