The Influence of Food Supply on the Parental Investment of Arctic Terns Sterna paradisaea

• Main Author: Uttley, John
• Format: Thesis
• Language: English
• Published: ProQuest Dissertations & Theses 1991
• Subjects: Arctic; Arctic tern; Sterna paradisaea
• Online Access: http://theses.gla.ac.uk/78296/; http://theses.gla.ac.uk/78296/1/11008028.pdf

The aims of this project were to examine the effects of food shortage on the breeding biology of the Arctic tern Sterna paradisaea, a small, surface-feeding seabird with a short foraging range in the breeding season. A comparative approach was adopted, and various aspects of Arctic tern breeding biology were studied both on Shetland, where the main prey of Arctic terns, lesser sandeels Ammodytes marinus are less available than they have been previously, and other suitable prey are absent, and on Orkney, where food supply for Arctic terns appears to be better. Further data from Coquet Island, Northumberland, collected during a broader study, of which this study is a part, were also utilised. Investment in egg production was investigated through measurements of courtship feeding rates and clutch size, egg size and quality. This was followed by analyses of the time budgets of male and female Arctic terns during laying, incubation, hatching, early chick life and later chick life. The results showed that egg production was little affected, if at all, by food shortage, and evidence was presented to show that adjustments in male and female investment patterns enabled the maintenance of clutch quality. This is discussed in relation to Arctic terns' breeding strategy. The performance of adult Arctic terns feeding chicks was assessed in detail, in relation to food supply, brood age and weather conditions. Differences in the diet of chicks and the rate at which they were provisioned were discussed and the profitability of feeding sandeels to chicks was shown to be lower on Shetland than on Orkney. Potential reasons why Arctic terns did not exploit alternative prey to a greater extent were discussed. The behaviour of Arctic terns in a situation of food shortage was also shown to influence the rate at which young were provisioned. Conspecific kleptoparasitism had a very large impact on chicks' food intake rates at the poor food supply site, and the occurrence of kleptoparasitism and its frequency for different prey categories was shown to concur with predictions from the literature. A model showed that the risk of kleptoparasitism could not explain the lack of large prey items in the diet of chicks in terms of energetics, and other explanations were discussed. Diversion of food from chicks to females was also more frequent where food supply was poor, and the implications of this were also discussed. Finally the results of a pilot study into the free-ranging energetics of Arctic terns, as measured by the doubly-labelled water method, were presented. Although inconclusive, the results suggested that Arctic terns raising young in conditions of food shortage may incur high levels of energy expenditure. The usefulness of the doubly-labelled water technique is discussed in the light of its potential behavioural consequences.