Breeding Strategies of the Blue Tit and Coal Tit (Parus) in Mainland and Island Mediterranean Habitats: A Comparison

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Abstract
The breeding ecology of blue tits [Parus ater] shows very different patterns in Provence and in Corsica. For both species the onset of the breeding season is delayed by .apprx. 3 wk on the island and the clutch size is reduced by .apprx. 30%. Corsican tits never have 2nd broods whereas 36% of blue tits and 60% of coal tits do have 2nd broods on the mainland. Breeding success is 6 .cntdot. 4 young raised per pair for the blue tit and 9 .cntdot. 5 for the coal tit on the mainland, as compared with 2 .cntdot. 6 and 3 .cntdot. 0 respectively in Corsica. The proportion of breeding adults older than 1 yr is only slightly higher on the island. These results which illustrate a lower population turnover on the island are discussed in the light of current theories dealing with the evolutionary significance on clutch size and associated life history parameters. Insular characteristics of the food supply and its variability on a year round basis are shown to be important factors responsible for these differences in population ecology. Comparisons of the growth rates of nestlings and of feeding frequencies between the mainland population and the Corsican population do not support they hypothesis that low reproductive rates on the island could be attributed to intraspecific competition. Nor do these results support the view that breeding ecology is determined through mechanisms of optimization of reproductive effort in a trade-off between clutch size and associated life history parameters. They fit Ashmole''s hypothesis on the significance of clutch size. It is concluded that a low amount and only a small surplus of food supply during the breeding season are sufficient to explain why the breeding ecology of Corsican tits is so different from the of the continental ones.