Distribution, abundance, and habitat association of riparian-obligate and -associated birds in the Oregon Coast Range

We studied the abundance, distribution, and habitat associations of the aquatic-foraging riparian-associated vertebrate community along four stream basins transecting managed forests in the Oregon Coast Range, 1992-1994. The riparian-associated community we observed consisted primarily of birds with few observations of mammals. Belted kingfishers (Ceryle alcyon), American dippers (Cinclus mexicanus), great blue herons (Ardea herodias), and mallards (Anasplatyrhynchos) comprised >85% of these observations, but we observed only one group (≥1 individual observed together) from this community for each kilometer of stream surveyed. Bird abundances among years were not different (all P > 0.05). Species distribution was affected by stream order, stream basin, and season in each species, but to varying degrees. Belted kingfishers, common mergansers (Mergus merganser), great blue herons, green herons (Butorides striatus), and mallards were more abundant in larger, 6(th)-order streams than in smaller, 4(th)-order streams (P < 0.05). Dippers used step channel units disproportionally more and riffles disproportionately less than expected (P < 0.5). Similarly, kingfishers used fewer riffles and more pool channel units than was expected (P < 0.5). Key habitat components that were predictive of use were species specific. Most notably, the presence of a forested riparian area, streamside trees, and valley walls that constrain the stream were important predictors of use by the three most abundant species; dippers, kingfishers, and great blue herons. Monitoring programs to assess populations of these species in mountainous habitat must be sensitive to the potential effects of stream order, basin, and season and encompass a large spatial and temporal extent.