Evaluation of the size and composition of nonbreeding surplus in a pied flycatcher Ficedula hypoleuca population: Removal experiments in Germany and Russia

Abstract

Sternberg H., V.G. Grinkov, E.V. Ivankina, T.A. Ilyina, A. Kerimov & A.Schwarz 2002. Evaluation of the size and composition of nonbreeding sur-plus in a Pied Flycatcher Ficedula hypoleuca population: removal experi-ments in Germany and Russia. In: Both C. & T. Piersma (eds) The aviancalendar: exploring biological hurdles in the annual cycle. Proc. 3rd Conf.European Orn. Union, Groningen, August 2001. Ardea 90(3): special issue461-470.According to calculations, the annual proportion of non-breeding males inthe Pied Flycatcher Ficedula hypoleucain a study area in Lower Saxony(LS), Germany, was about 80% in yearlings (Sternberg, 1989). In order todetect non-breeders in populations and to determine their age and colourtype, removal experiments were conducted in 1974 and 1976 on long-termused plots in LS and in 2000 on newly arranged plots in the MoscowRegion (MR), Russia. The breeding populations of these study areas weresimilar in age structure but differed in recruitment rate (9% and <1%,respectively). During 2-3 weeks of the pre-breeding period, we removed allnewly arrived males from the plot every day and kept them in an aviary. InLS, captive males were released in the same study area 3d before and 2 dafter median onset of egg-laying in non-experimental plots in 1974 and1976, respectively. In MR captive males were released 3 d before medianonset of egg-laying in non-experimental plots. The number of removedmales exceeded the number of males found on a control plot by about fourtimes in both regions, indicating an equal ratio of non-breeders in the popu-lations. The number of removed males was about four times higher in LSthan in MR due to the lower occupation rate of the new plots in MR. Afterreleasing the birds, similar proportions of birds bred in the plots during thesame season in both regions. In LS, a further proportion of released malesbred in three subsequent seasons. Assuming a mean annual mortality ofadult birds of 50%, nearly all survivors out of the removed males bred inthe LS study area in subsequent years. The proportion of subsequent breed-ers appears to be the same in MR. In both populations, the birds that werereleased and bred during the same season were older and more conspicu-ously coloured than non-breeders. The results suggest that high portions ofnon-breeders and a delay in the start of first breeding may occur both athigh and low population densities.Key-words: Ficedula hypoleuca- removal experiments - non-breeders -population surplus.