Food availability and population processes: severity of nutritional stress during reproduction predicts survival of long‐lived seabirds

Abstract

Summary 1. 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.