Changes in the breeding bird communities on mires and in surrounding forests in southeastern Norway during a 40-year period (1976-2015)

Abstract

The breeding bird communities of 18 mires and surrounding forests in southeastern Norway were censused in 1976-77 and in 2015. We found that 53% of the mire species with sufficient data for analyses showed significant changes. Red-throated Diver Gavia stellata, Common Crane Grus grus, Wood Sandpiper Tringa glareola and Tree Pipit Anthus trivialis increased, whereas Northern Lapwing Vanellus vanellus, Black-headed Gull Chroicocephalus ridibundus, Meadow Pipit Anthus pratensis and Yellow Wagtail Motacilla flava decreased. There were also near significant decreases of Eurasian Curlew Numenius arquata and Eurasian Skylark Alauda arvensis. Population changes did not differ between short- and long-distance migrants. Species with marginal populations on mires declined more than mire specialist species, suggesting an indirect negative influence of problems in other habitats. Overall, there was a significant 19% decline in number of mire species, but a non-significant 7% increase in number of individuals. The bird community in the forests surrounding the mires showed significant population changes for 42% of the species with sufficient data for analyses, with increases in many resident forest species, but less so for migrants. Overall, there was a near significant 12% increase in number of forest species, and a significant 28% increase in number of individuals. Mire- and forest-associated species did not differ in population trends. Among short-distance migrants (mire and forest species combined), species wintering in agricultural habitats had more negative population changes than species wintering in other habitats. Thus, the breeding bird community on and around mires in this part of Norway has undergone large changes during the last 40 years. We discuss our results in relation to general trends of bird communities in northern Europe.