Population dynamics in 20 sedentary and migratory passerine species of the Courish Spit on the Baltic Sea

Sokolov, L.V. (1999): Population dynamics in 20 sedentary and migratory passerine species of the Courish Spit on the Baltic Sea. Avian Ecol. Behav. 3: 23-50. I analysed trends of population dynamics in breeding populations of 20 sedentary and migratory passerines of the Courish Spit on the Baltic Sea. In the bulk of species in the 1960s and 1980s an increase was recorded, in the 1970s and 1990s a decline was evident. Breeding numbers and numbers of juveniles during post-fledging period were estimated by trapping in Rybachy-type traps during 3 months each year. In all species except Lesser Whitethroat Sylvia curruca and Barred Warbler S. nisoria a positive association between the numbers of juveniles during post-fledging period and the mean temperatures of April and May was revealed. The numbers of local juveniles trapped during the post-fledging period were significantly correlated with the numbers of breeding birds trapped in the subsequent year. The number of second-year birds in a popu- lation is significantly higher following a year with high numbers of juveniles. Our analysis suggests the population dy- namics in these passerines is shaped mainly by external factors such as temperature and human activity that influence the survival of adults, especially in winter and in spring, and their breeding success. Other factors, including density-dependent ones, that may have an impact on population numbers are probably of secondary importance.