Factors affecting avian species richness and density in riparian areas

Riparian areas are an important part of conservation efforts directed toward minimizing the effects of habitat loss on birds because riparian areas host a large number of bird species. We compared species richness and densities of breeding songbirds among 3 narrow (55-95 m) and 3 wide (400-530 m) forested-riparian areas with adjacent grassland-shrub buffer strips and 3 narrow and 3 wide forested-riparian areas without adjacent grassland-shrub buffer strips, in northeastern Missouri, USA. More bird species occurred in wide than in narrow forested-riparian areas (mean difference = 8.58, 95% CI = 4.82-12.35). Wide forested-riparian areas with and without adjacent buffer strips had similar numbers of species (mean difference = 0.50, 95% CI = -2.77-3.77). Narrow forested-riparian areas with adjacent buffer strips had more species than narrow forested-riparian areas without adjacent buffer strips (mean difference = 9.67, 95% CI = 5.43-13.90). A mixed model with a fixed effect of width had the most support for predicting density of ovenbird (Seiurus aurocapillus), Acadian flycatcher (Empidonax virescens), Kentucky warbler (Oporornis formosus), gray catbird (Dumetella carolinensis), common yellowthroat (Geothlypis trichas), northern cardinal (Cardinalis cardinalis), and indigo bunting (Passerina cyanea). The null model had the most support for wood thrush (Hylocichla mustelina), Louisiana waterthrush (Seiurus motacilla), and field sparrow (Spizella pusilla). Wide forested-riparian areas provided breeding habitat for more bird species than narrow forested-riparian areas, especially forest area-sensitive species. The addition of grassland-shrub buffer strips adjacent to forested-riparian areas increased species richness in those areas and provided habitat for gray catbird, common yellowthroat, northern cardinal, field sparrow, and indigo bunting.