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

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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/10 ha were .apprx. 11, 1 and 6 in coniferous plots and .apprx. 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. Fluctuations in the great tit and blue tit breeding populations are closely related to winter food availability. Among variables describing winter climate and food supply the beechmast production was the most important for explaining the population fluctuations of these 2 spp. 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; 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 3 tit species, statistical models for analysis of bird population fluctuations are discussed.