Scientific publications

Studies of peripheral populations are relevant due to the fact that their organisms face the most severe environmental conditions under which they may exist and reproduce. Species abilities to spread as well as mechanisms preventing this process can best be revealed at the edges of the distribution range. One priority of such studies is to estimate the population dynamics and sex and age population structure. In Karelia, NW Russia, more than 40% of bird species occur near the range boundaries (Zimin 2001), including Sylvia and Phylloscopus warblers. Besides specifics of the range periphery, northern environmental conditions influence the birds. In addition, intensive forest management arrangements implemented in Karelia during the 20th century substantially changed relevant habitats and caused changes in bird distribution and population size. Bird studies including trapping, marking, work with nests, census, observations, and application of molecular genetic techniques have been carried out in this region for more than 40 years. Considerable annual fluctuations in number of birds (especially females) and sex ratio imbalance in favor of adult males were registered in the studied populations. To test the hypothesis that there is no original predominance of males in broods of these populations, we determined the sex of offspring via amplification of the СHD gene. The sex ratio in broods did not differ from 1:1. In turn, the analysis of long-term trapping data indicated the predominance of males among juvenile warblers during post-breeding dispersal and autumn migration in most seasons. Males constantly outnumbered females among adults. In addition to the reasons behind changes in sex ratio and bird numbers, the discussion will address the hypotheses about higher survival rates of males, characteristics of northern range periphery (remoteness from wintering grounds, weather conditions, etc.), and human impact. The study was conducted with the support of RFBR (projects NN 06-05-64368_a, 15-05-03493_a, and 12-04-31872).