Searching for Density-Dependent Regulation in a Population of Pied Flycatchers Ficedula hypoleuca Pallas

Abstract

(1) Breeding data from a population of pied flycatchers (Ficedula hypoleuca) nesting from 1948 to 1964 in the Forest of Dean, Gloucestershire, U.K. were analysed for density-dependent changes in clutch size, mortality and migration rates. (2) High breeding population densities followed seasons in which many young were fledged, but the increased numbers of breeding birds resulted from high levels of immigration as well as increased recruitment of birds raised in the study area in the previous breeding season. (3) When nestling mortality was high, a smaller proportion of birds breeding in the area in the following year were immigrants. (4) During the first 7 years of the study, high breeding population densities were associated with small clutch sizes. (5) Nestling mortality was not correlated with breeding population densities. (6) The number of birds in the study area at the end of the breeding season accounted for about 76% of the variation in rates of return of first-year birds to breed in the area the following year, with a lower proportion of birds returning following high-density years.