Effects of habitat type and degradation on avian species richness in GreatBasin riparian habitats

The overwhelming majority of bird species in the Great Basin region are fou nd in riparian habitats. However, most previous research on the impact of c hange in habitat condition through degradation on these bird communities fa iled to account for the large intersite differences in both habitat type an d extent of degradation. We examined songbird communities in 4 riparian hab itat types (meadows, willow-, birch-, and, aspen-dominated forest stands) d uring summers 1994 (last year of a 7-yr drought) and 1995 (following the 6t h wettest winter recorded) in the Toiyabe Mountain Range of central Nevada. Habitat degradation significantly influenced bird species richness in ripa rian areas, but the impact was dependent upon habitat type. While meadow bi rd communities were affected adversely by habitat degradation, with signifi cant 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 degrada tion may have influenced distribution of American Robins (Turdus migratoriu s) and Yellow Warblers (Dendroica petechia), but habitat type was the best predictor of abundance for House Wrens (Troglodytes aedon), Red-naped. Saps uckers (Sphyrapicus nuchalis), Warbling Vireos (Vireo gilvus), and Brewer's Blackbirds (Euphagus cyanocephalus). Avian species diversity in meadow hab itats may be linked to moisture levels during specific times of the year. D iversity increased during the pre-migratory period of the dry year (1994) w hen compared with that of the breeding season, but was unchanged in the wet year (1995).