Activity budgets, diet and breeding success of KittiwakesRissa tridactylaon the Isle of May

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Abstract
We collected data on activity patterns (brood attendance, durations of feeding trips and feeding rates) of parent Kittiwakes Rissa tridactyla and the food fed to chicks in 2 breeding seasons at the same colony. In 1989, trip duration increased markedly towards the end of the nestling period. Pairs attempted to increase the feeding rate of their young by both adults foraging simultaneously rather than alternately. This response was more pronounced in pairs with two chicks (b/2s), i.e. those with greater food requirements. Estimates of the energy value of food delivered by the pair to the brood suggested that, particularly for b/2s at the end of the season, amounts were insufficient to meet the chicks' requirements. However, despite this shortfall most chicks survived to fledging. In 1990, Kittiwakes fed their young on smaller sandeels Ammodytes spp which had a lower energy density than those in 1989. Feeding rates were also low. We estimated that for most of the chick rearing period energy intakes for the young were below those required. Breeding success was only 0.17 chicks fledged/completed nest, the lowest value for at least 10 years.