Breeding and Wintering riverine birds at the Aurland river, western Norway during post-regulation conditions

Abstract

The riverine bird community of the river Aurland was studied in 1989 and 1990 during post-regulation conditions, focusing on both the breeding bird community and the winter bird community. Although regulation has strongly reduced the spring and summer flow, the riverine bird community is within the normal range for the region with regard to both species composition and the population density along the rivers. During the breeding season three species, the dipper, white wagtail and the common sandpiper, are the regular breeders. The three species, all of which are benthic insect feeders, exhibited population densities above the average for rivers in western Norway, based on a comparison with population from 38 other rivers in three counties. As wagtails and sandpipers disappear during late summer and early autumn (migrants), they are replaced by two new species over the wintertime, grey heron and goosanders, both of which are piscivorous. Moreover, the winter community is species poor, but this is normal for similar rivers in the region. The density of the species seems normal, but probably above average for dippers. The results from this study, showing a viable riverine bird community, should be viewed against the fact that the food situation (benthic insects) has probably improved from pre- to post-regulation conditions in the river ecosystem.