Ardea
Official journal of the Netherlands Ornithologists' Union

login


[close window] [previous abstract] [next abstract]

Blondel J., Clamens A., Cramm P., Gaubert H. & Isemann P. (1987) Population studies on tits in the Mediterranean region. ARDEA 75 (1): 21-34
In the first part of this paper emphasis is given on the large variation in clutch size of the Blue Tit within the Western Mediterranean area. This between-habitat variation is due to the heterogeneity of many patchily distributed habitats of different quality (evergreen oak woodland, deciduous oak woodland, conifers) as well as to the physiographic diversity of the region. Comparative studies in progress on the breeding patterns of the Blue and the Great Tit in evergreen oak woodland (Quercus ilex) and in deciduous oak woodland (Q. pubescens) show that there are important differences between these two kinds of habitats for such parameters as the onset of breeding, clutch size and breeding success. Experiments are in progress in order to assess the role of the food supply in these differences, especially in the timing and the length of food availability as well as the quantity of the food supply. Detailed population studies are conducted mostly on the Blue Tit between an insular site (Corsica) and a continental one (Mont-Ventoux). Striking differences in the functioning of these populations cannot be explained in the light of theories of island biogeography. Paradoxally there seem to be on the island environmental constraints which limit the breeding time between two fixed limits. Suppose that the relation between laying date and local survival of the juveniles is steeper in Corsica than on the mainland. This would imply a strong competition and a greater investment for young to increase their chance of survival. This would lead to a smaller clutch size. Anyway there is on the island a reduced breeding productivity without a reduction in adult mortality which is as high as on the mainland. Actual clutch size cannot be interpreted in the light of a trade-off between fecundity and survival.


[close window] [previous abstract] [next abstract]