Habitat Heterogeneity and Life-History Variation of Mediterranean Blue Tits (Parus caeruleus)

Abstract

The extensive variation in breeding traits of Mediterranean Blue Tits (Parus caeruleus) is hypothesized to result from large differences in the timing and abundance of food resources, depending on whether the dominant tree species of the habitat is deciduous (Quercus pubescens) or evergreen (Q. ilex). Data were collected on tree phenology, food abun3;2;­ dance (caterpillars), and breeding traits of tits in one mainland deciduous habitat, two main3;2;­ land evergreen habitats, and one evergreen habitat on the island of Corsica. In the mainland deciduous habitat, an early breeding time and a large clutch size were associated with an early and abundant food supply. In the evergreen habitats (both on mainland and on Corsica), the leafing process occurred three weeks later and the abundance of caterpillars was much lower. On Corsica, tits started to lay three weeks later than in the deciduous mainland habitat and laid about 30% fewer eggs. As in the deciduous mainland habitat, the breeding process seemed to be adjusted to the patterns of food availability. In the two mainland evergreen habitats, tits started to breed earlier and laid more eggs than expected from the patterns of food availability so that they mismatched the best period to raise their young. The apparent maladaptation of tits in these evergreen mainland habitats is hypothesized to result from an asymmetric gene flow between rich deciduous habitats (source), where well-adapted birds produce many fledglings, and poor evergreen habitats (sink), where the density is maintained through immigration from rich habitats.