Sternberg H., Grinkov V.G., Ivankina E.V., Ilyina T.A., Kerimov A.B. & Schwarz A. (2002) Evaluation of the size and composition of nonbreeding surplus in a Pied Flycatcher Ficedula hypoleuca population: Removal experiments in Germany and Russia. ARDEA 90 (3): 461-470

According to calculations, the annual proportion of non-breeding males in the Pied Flycatcher Ficedula hypoleuca in a study area in Lower Saxony (LS), Germany, was about 80% in yearlings (Sternberg, 1989). In order to detect non-breeders in populations and to determine their age and colour type, removal experiments were conducted in 1974 and 1976 on long-term used plots in LS and in 2000 on newly arranged plots in the Moscow Region (MR), Russia. The breeding populations of these study areas were similar in age structure but differed in recruitment rate (9% and <1%, respectively). During 2-3 weeks of the pre-breeding period, we removed all newly arrived males from the plot every day and kept them in an aviary. In LS, captive males were released in the same study area 3 d before and 2 d after median onset of egg-laying in non-experimental plots in 1974 and 1976, respectively. In MR captive males were released 3 d before median onset of egg-laying in non-experimental plots. The number of removed males exceeded the number of males found on a control plot by about four times in both regions, indicating an equal ratio of non-breeders in the populations. The number of removed males was about four times higher in LS than in MR due to the lower occupation rate of the new plots in MR. After releasing the birds, similar proportions of birds bred in the plots during the same season in both regions. In LS, a further proportion of released males bred in three subsequent seasons. Assuming a mean annual mortality of adult birds of 50%, nearly all survivors out of the removed males bred in the LS study area in subsequent years. The proportion of subsequent breeders appears to be the same in MR. In both populations, the birds that were released and bred during the same season were older and more conspicuously coloured than non-breeders. The results suggest that high portions of non-breeders and a delay in the start of first breeding may occur both at high and low population densities