Effects of Habitat Type and Degradation on Avian Species Richness in Great Basin Riparian Habitats

The overwhelming majority of bird species in the Great Basin region are found in riparian habitats. However, most previous research on the impact of change in habitat condition through degradation on these bird communities failed to account for the large intersite differences in both habitat type and extent of degradation. We examined songbird communities in 4 riparian habitat types (meadows, willow-, birch-, and aspen-dominated forest stands) during summers 1994 (last year of a 7-yr drought) and 1995 (following the 6th wettest winter recorded) in the Toiyabe Mountain Range of central Nevada. Habitat degradation significantly influenced bird species richness in riparian areas, but the impact was dependent upon habitat type. While meadow bird communities were affected adversely by habitat degradation, with significant drops in species richness on degraded sites, bird species richness in forested riparian habitats was consistently greater on degraded sites. Data for the 6 most common species seen during our study indicated that degradation may have influenced distribution of American Robins (Turdus migratorius) and Yellow Warblers (Dendroica petechia), but habitat type was the best predictor of abundance for House Wrens (Troglodytes aedon), Red-naped Sapsuckers (Sphyrapicus nuchalis), Warbling Vireos (Vireo gilvus), and Brewer\u27s Blackbirds (Euphagus cyanocephalus). Avian species diversity in meadow habitats may be linked to moisture levels during specific times of the year. Diversity increased during the pre-migratory period of the dry year (1994) when compared with that of the breeding season, but was unchanged in the wet year (1995)