HABITAT HETEROGENEITY AND LIFE-HISTORY VARIATION OF MEDITERRANEAN BLUE TITS (PARUS-CAERULEUS)

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 d ominant tree species of the habitat is deciduous (Quercus pubescens) o r evergreen (Q. ilex). Data were collected on tree phenology, food abu ndance (caterpillars), and breeding traits of tits in one mainland dec iduous habitat, two mainland evergreen habitats, and one evergreen hab itat on the island of Corsica. In the mainland deciduous habitat, an e arly breeding time and a large clutch size were associated with an ear ly and abundant food supply. In the evergreen habitats (both on mainla nd and on Corsica), the leafing process occurred three weeks later and the abundance of caterpillars, was much lower. On Corsica, tits start ed 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 availab ility. In the two mainland evergreen habitats, tits started to breed e arlier and laid more eggs than expected from the patterns of food avai lability so that they mismatched the best period to raise their young. The apparent maladaptation of tits in these evergreen mainland habita ts is hypothesized to result from an asymmetric gene flow between rich deciduous habitats (source), where well-adapted birds produce many fi edglings, and poor evergreen habitats (sink), where the density is mai ntained through immigration from rich habitats.