Use of a new standardized habitat survey for assessing the habitat preferences and distribution of upland river birds

Assessments of the habitat requirements of river birds are central to understanding their distribution and abundance. Here, we make an initial appraisal of the suitability for this purpose of a new standardized method of river habitat survey (RHS) developed by the Environment Agency (EA). We carried out RHS and recorded the presence of five common birds along 74 upland Welsh streams. RHS provided significant and meaningful correlates with bird distribution: Dippers Cinclus cinclus and Grey Wagtails Motacilla cinerea showed a significant preference for sites with tree-related features, while Common Sandpiper Actitis hypoleucos preferred streams with few trees but with more rough pasture and riparian wetlands. Dippers also showed a significant preference for streams with bridges and walls, often used as nesting or roosting sites. Mallards Anas platyrhynchos and Goosanders Mergus merganser both preferred sites with smoother flows, finer substrates and more emergent vegetation. For all species, multiple discriminant analysis (MDA) on RHS data predicted presence with a success rate of 50-81%. The distribution of Grey Wagtails and Dippers was best predicted by RHS variables from the channel, flow, bank and riparian zone; Common Sandpiper and Goosander distribution was predicted best by channel and flow characters, and that of Mallard by channel features alone. In three species (Dipper, Goosander and Mallard) stream chemistry (pH) improved predictive ability. We conclude that RHS, although designed initially for more general purposes, is a potentially important tool for describing and predicting river bird distribution. Future developments should include assessments of which RHS data best predict bird distribution across a wider array of river types and species. Incorporating other important influences on distribution, such as water chemistry, should both enhance predictive ability and allow further development to the role of river birds as ecological indicators.