Winter Mortality and Food Supply in Tits Parus spp.

Abstract

Changes in survival and immigration in response to food provision in autumn and winter were studied in colour-banded populations of willow tits Parus montanus and crested tits P. cristatus. The extra food improved winter survival substantially and induced autumn immigration and settling. Food influenced survival, at least partly, by decreasing the risk of predation. Improved winter survival of the fed populations led to doubled breeding populations in the following spring, although the extra food was withdrawn two to four weeks before laying. It is concluded that in these tits, food abundance is crucial to winter survival, which limits the size of the breeding population.