Breeding time and Breeding Performance of the Blue Tit (Parus Caeruleus) in two Mediterranean Habitats

Abstract

In a population of birds the date of egg laying and clutch size largely depend on the age structure, the genetical structure of the population in a given year, and the quality and variability of the habitat (van Noordwijk et al. 1981 a and b, Martin 1987). To investigate the last point, we studied a Blue Tit (Paruscaeruleus) population breeding in two neighbouring habitats in mediterranean France (see Blondel et al. 1987, Isenmann et al. 1987 for details). The first habitat is dominated by evergreen Holm Oaks (Quercus ilex), the second by deciduous Downy Oaks (Quercus pubescens). The vegetation of the former habitat reflects the climatic constraints of the mediterranean zone where evergreen plants are widespread and dominant, whereas the latter habitat is more representative of temperate European habitats. The peak of food availability in spring occurs later, is smaller and lasts longer in the evergreen oak habitat than in the deciduous habitat (Cramm 1982, Isenmann et al. 1987, Clamens 1988). Blue Tits in the evergreen habitat actually lay fewer eggs per clutch and start to breed later than those in the deciduous habitat. In this paper, we analyse the differences in clutch size and breeding success between and within years as a clue of the explanations previously suggested to account for the between habitat differences in Blue Tit reproductive biology (Blondel et al. 1987, Clamens and Isenmann 1989).