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Habitat differences in allocation of eggs between successive breeding attempts in great tits (Parus major)1

Abstract: The effect of habitat heterogeneity on animal behaviour and reproduction has recently captured serious attention in population and conservation biology. The great tit (Parus major) is a facultative double-brooded species that prefers deciduous forests as breeding habitats. However, it is able to reproduce in managed coniferous forests where nest boxes are provided. During 1999–2002, we measured various reproductive parameters of great tits, including double breeding, in a heterogeneous habitat complex consisting of both deciduous and coniferous forests. Probability of laying a second clutch after the hatch of the first clutch did not differ significantly between habitats. However, clutch size was allocated between two successive breeding attempts more equally in coniferous than in deciduous forests. To our knowledge, this is the first time that such a difference in seasonal breeding patterns between adjacent habitats has been demonstrated in birds. However, the total number of offspring fledged per pair did not differ significantly between habitats. Possible proximate and ultimate causes of the observed habitat differences are discussed. We suggest that habitat-specific allocation of reproductive investment between successive breeding attempts plays an important role in optimizing breeding tactics by facultative multiple-brooded bird species in a heterogeneous environment, potentially serving as a useful mechanism facilitating their adaptation to novel habitats.