Species richness and structure of a breeding passerine bird community in a spruce-dominated boreal forest in central Norway: stability from 1960s to 2013

The density of the breeding passerine bird community in a spruce-dominated forest in central Norway was studied in an area of one km2 during the years 1960 and 1962-1972. In the present study I report on the structure of the passerine community in 2013 and species richness in the periods 1985-1986, 2000-2001 and 2010-2013 in the same forest area, and compare the results with those from the 1960s. The community density during 1960-1972 varied between 142 and 195 territories/km2, with a mean of 170. The structure of the community, based on the species' relative densities (the percentage share of each species in the total amount of observations) and the species richness, was basically unchanged. Thirty-seven passerine species were recorded as territorial within the study area, 34 in 1960-1972 and 33 in 2013. Five species held about half (49%) of the community in 1960-1972: European Robin Erithacus rubecula, Song Thrush Turdus philomelos, Chaffinch Fringilla coelebs, Common Chiffchaff Phylloscopus collybita and Dunnock Prunella modularis, for each of which the mean relative density varied from 6.2 to 11.8%. The same species, except for Dunnock that was replaced by Willow Warbler Phylloscopus trochilus in 2013, made together 53% of the passerine community. When combining the years 1960-1972 and 2013, Song Thrush and Hooded Crow Corvus cornix had increased in relative densities, Dunnock, Eurasian Blackbird Turdus merula and Willow Tit Poecile montanus had decreased, while European Robin and Chaffinch were the most stable species. Twenty-nine species, i.e. 74% of the total number of species (39), were recorded in each of the four periods. The remaining species, being absent in one or more periods, accounted each for less than 1%, in total 6%. Despite some numerical changes, the passerine bird community has shown a considerable stability in species richness and structure across the period of 50 years since 1960