Density-Dependence in Breeding Success of the Pied Flycatcher (Ficedula hypoleuca)

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Abstract
The effect of breeding density on different reproductive parameters was tested experimentally in the pied flycatcher in 1981 and 1982 near Uppsala, central Sweden. Nest boxes were provided at 2 densities resulting in high (2 pairs/ha) and low breeding density (< 1 pair/ha). Pairs breeding at high and low density started egg-laying (median) at the same dates and did not differ in polygyny frequency or age. Breeding density had no effect on clutch size or hatching success. Fledgling numbers, nestling weight and tarsus length were slightly but significantly affected in a density dependent way, presumably because of food competition between breeding pairs. Density-dependent effects were most marked in the year with unfavorable weather conditions probably reducing food availability. Intraspecific competition for food presumably is less important in the natural situation with intense intra- and interspecific completion for a limited number of nest holes.