SURVIVAL AND POPULATION-DYNAMICS OF NUTHATCHES SITTA-EUROPAEA BREEDING IN NATURAL CAVITIES IN A PRIMEVAL TEMPERATE FOREST

Data on breeding densities of Nuthatch were collected in three types of mature tree stands in Bialowieza National Park, E Poland, during 1975-90. Detailed observations on breeding and survival were made during 1987-89. The highest densities occurred in swampy stands (max. 4.8 territories per 10 ha), they were 10-47% lower in oak-hornbeam stands, and in coniferous stands densities did not exceed 1.2 territories per 10 ha. Nuthatch numbers reached a low in 1979, then increased over fourfold to a maximum in 1990. In contrast to the situation in Scandinavia, Nuthatch numbers in spring were not significantly correlated with the severity of the preceding winter, though their numbers seemed to be influenced by autumn seed supply and availability of caterpillars in the preceding spring. Yearly survival rates were close to 50%. Winter survival equaled that in spring and summer, and was even higher in the unusually mild winter of 1989/90 which had a rich supply of hornbeam seeds. Egg-laying in BNP commenced between 5 April and 26 April in different years. Clutches usually contained 6-9 eggs. On average two thirds of the nesting attempts resulted in fledged young, though nesting success varied much between plots. Nest losses were among the highest reecorded in European populations. Nests containing young were destroyed two to four times as often as nests with eggs, suggesting that the losses were mainly due to predation.