Effects of Food Addition to Willow Tit Parus montanus and Crested Tit P. cristatus at the Time of Breeding

Abstract

Before and during the two breeding seasons of 1976 and 1977 the tits were fed with sun-flower seeds and nutrient enriched tallow in a 1.8 km2 area. A 5.5 km2 area was used as a control. The tits were not fed in experimental area in 1978. The aim was to find whether the tits take advantage of a rich food supply at the time of breeding. Laying was advanced in both species by 2-8 d in 1976 and 1977 but not in 1978. Clutch-size and number of fledglings were not significantly affected in any of the species. Fitness was improved by increasing the survival of the offspring rather than their number. The nestlings of the fed Crested Tits were heavier. There was a slight trend towards more second broods in the experimental area.