On the constancy of annually repeated bird censuses

Abstract

The bird population of an area in SE Finland was censured by almost daily mapping from 13 May to 3'1 July 1981 . The size of the area is 16 ha: 12 ha forest, 2 ha dense young tree plantations and 2 ha meadows. Mixed coniferous forest of medium productivity is the dominant habitat type. During the main breeding season, June, the number of inhabited territories, summed up for 5-day periods, varied between 48 and 57 . The total was 66 . During earlier summers at least 30 pairs nested in places not covered by territories of pairs or single males resident in 1981 . Thus the carrying capacity of the area is about 100 breeding pairs, twice the number present in any period of the main breeding season. The significance of predation in the numbers of birds is briefly discussed.