Fluctuations of Tits (Paridae) in Denmark and Their Relations to Winter Food and Climate

Abstract

Fluctuations in the breeding populations of tits (Paridae) were studied in North Zealand, Denmark, in 1964-1981 on plots with a surplus of nestboxes. Average breeding densities in pairs per 10 ha were about 11, 1 and 6 in coniferous plots and about 15, 5 and 1 in deciduous plots for the Great Tit Parus major, the Blue Tit P. caeruleus and the Coal Tit P. ater, respectively. It was concluded from the data that fluctuations in the Great Tit and Blue Tit breeding populations are closely related to winter food availability. Specifically, among variables describing winter climate and food supply the beechmast production was by far the most important for explaining the population fluctuations of these two species. In addition severe winter climate had some negative effect on the Great Tit, while no such influence was found for the Blue Tit. The conclusions for the Coal Tit are less clear; however, the data suggest that the severity of the winter may be more important than the variation in food production. In addition to results for the three tit species, statistical models for analysis of bird population fluctuations are discussed.