The winter bird community of river corridors in eastern England in relation to habitat variables

Abstract

Most river corridors have been highly modified and managed but they still support diverse assemblages of birds. To aid conservation it is important to know which river corridor habitats support the greatest diversity and numbers of bird species. All birds were counted on three occasions in winter along 50 one km stretches of lowland rivers in eastern England, and habitat variables were recorded. Atotal of 81 species was recorded. Species richness was greatest on tidal stretches of river, followed by urban/amenity sites, with lowest richness on rural stretches. Mute Swans, Mallards and Moorhens were significantly more numerous at urban/ amenity stretches and were scarce or absent in headwater reaches. Three terrestrial species also occurred in significantly greater numbers in urban/ amenity stretches. No species was significantly more numerous in rural stretches. TWINSPAN analysis separated out tidal and urban/amenity stretches, while bird species were separated into those associated with riparian trees and shrubs, and those of more open stretches, with further groups associated with wider rivers and the tidal stretches. A CANOCO analysis showed river width to be the most significant factor explaining bird distributions, followed by presence of floodbanks, riparian tree cover and amount of thick marginal vegetation. The rivers studied and their immediate floodplains have long been managed and modified from source and this has an overriding influence on habitat quality and on the species richness and numbers of birds utilizing any particular stretch.