Environmental restrictions on reproduction in the Pied Flycatcher Ficedula hypoleuca.

I compared two populations of Pied Flycatchers Ficedula hypoleuca breeding in a coniferous forest with adverse weather conditions (‘marginal habitat’) and in a deciduous forest with a more favourable climate (‘good habitat’). Female mass was significantly larger during the reproductive cycle in the ‘good habitat’. The incubation periods were significantly shorter in the ‘good habitat’. Reproductive success was significantly higher in the ‘good habitat’. Heavier females during the incubation period in the ‘marginal habitat’ had larger clutches and higher breeding success. The incubation periods in the ‘marginal habitat’ decreased significantly with female incubation mass. Fledgling mass increased with mean ambient temperature and fledgling tarsus length decreased with mean precipitation during the nestling period in the ‘marginal habitat’. In unfavourable climatic conditions or in habitats with a low food availability, the energetic constraints on breeding cause a reduction in female body mass reducing clutch size and breeding success. My results suggest that environmental factors have a strong influence on the breeding success and productivity of populations in ‘marginal’ habitats, and thus determine the breeding range of populations.

Sanz J.J, ARDEA 83 (2): 421-430