STRUCTURE AND DYNAMICS OF A PASSERINE BIRD COMMUNITY IN A SPRUCE-DOMINATED BOREAL FOREST - A 12-YEAR STUDY

The breeding passerine bird community in a Norwegian spruce-dominated forest (c. 63-degrees-N) was studied in an area of one km2 during the years 1960 and 1962-72. The number of territorial species varied annua lly between 22 and 33 (mean = 27, coefficient of variation CV = 13%), and their combined density, the community density, from 142 to 195 ter ritories/km2 (mean = 170, CV = 10%). About half of the territories eac h year were defended by the same five species. Twenty-one species were recorded every year, and their annual combined densities accounted fo r 88-99% of the overall community density. The other 13 species record ed in the community were absent in one or more years. These were all l ow-density species, with a maximum of three territories/km2 recorded i n any single year. The mean relative species turnover rate between two adjacent years was 0.15, CV = 42%. The variation (CV) in population d ensity of the different species was significantly negatively correlate d (r = -0.86) with their average population density during the 12 year s. Although some species showed some similarity in their fluctuation p atterns, none showed a wholly similar pattern, indicating that the dif ferent species were influenced by different combinations of factors.