Citation: Pichl, H. (1997) The life-history trade-offs constraining clutch size in the Kittiwake. Unpublished candidatus scientiarum thesis, Institutt for biologi, Universitetet i Tromsų, Tromsų, Norway. 76 pages.
Key words: Life history evolution, cost of reproduction, brood size manipulation, adult survival, offspring recruitment, Rissa tridactyla.
Abstract: Though the costs of reproduction in birds have recently received much attention, and many brood size manipulation experiments have been conducted, most of them have been restricted to short-lived species. I carried out a brood size manipulation of the Kittiwake, a seabird with an intermediate annual survival rate. Manipulation assigned experimentally enlarged (three chicks), reduced (one) and control broods (two) by random to a sample of 267 breeding pairs. The manipulated brood sizes were within the natural range of Kittiwake clutch sizes. Among the parameters recorded were proportion of nests losing young, age at chick loss, fledging success, and number of offspring produced; parental body mass, mass loss, and body condition early and late in the chick rearing period; re-sighting rate of adults in the following breeding season, frequency of mate and nest-site change; clutch sizes, egg volumes, hatching success and proportion of chick loss during the following breeding season. I found clear evidence of both inter- and intragenerational trade-offs within and between seasons: among others, fledgling weight of chicks and late body condition of female parents decreased with increasing brood size. Also fledging success decreased with increased brood size, but the Kittiwakes were nevertheless able to raise additional chicks. This did, however, not result in a significant relation between treatment and adult re-sighting rate in the following year. But hatching success, and frequency of chick losses and total breeding failure indicated the existence of costs of reproduction in the Kittiwake. I discuss these findings in relation to trade-offs and the optimal clutch size in the Kittiwake. Considering some model assumptions on chick recruitment and adult reproductive value, I come the conclusion that my findings cannot explain why the most common clutch size in Kittiwakes is two, rather than three eggs. I discuss further hypotheses which could explain the difference between the most common and the seeming optimal clutch size. As the stochastic environment Kittiwakes are adapted to can be responsible for that difference, I compare my findings with the results of a previous, very similar study which was carried out in the same colony. I can give some support to the hypothesis that responses to treatment should vary between years.
Related publications: For reasons that are within the responsibility of the remaining co-authors (and beyond my control), the findings reported in the thesis have not yet been published. As a substitute, I have made my whole thesis available for download above (and of course you can order a paper version by interlibrary loan).