Effects of recreational activity and livestock grazing on habitat use by breeding birds in cottonwood forests along the South Fork Snake River

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More than any other habitat in western North America, arid-land woodlands are centers of high diversity and abundance of birds. Because these habitats are fragmented and limited in distribution, western riparian birds might be particularly vulnerable to human-caused disturbances. During a four-year study, the author examined the influences of land-use practices in relation to cottonwood forest-patch dynamics on bird community and vegetative characteristics in southeastern Idaho. Patterns in bird community characteristics of 34 species, relative abundances of individual species and nest guilds, and vegetation structure were compared among three land uses (areas managed for livestock grazing [grazed], areas managed as campgrounds [recreation], and areas not managed for grazing or recreation but for riparian and wildlife habitat values [unmanaged]) and three patch-size classes (small [<1–3 ha], medium [>3–10 ha], and large [>10–204 ha]). Overall species richness, diversity, evenness, and turnover remained fairly constant among all land uses. On average, species numbers and relative abundance appeared to be most reduced by recreational activities except in large patches managed for recreation. Few differences existed between grazed and unmanaged sites in overall mean number of species or mean number of individuals observed per survey visit. However, distribution and abundance of individual species, and species grouped by nest layer and nest type, varied significantly among land-use activities and patch sizes. Vegetation structural characteristics within the ground, shrub, and canopy layers were positively correlated with abundance of birds nesting in those layers. Ground-nesting species (veery and fox sparrow) were most susceptible to disturbances created by livestock grazing and were also most sensitive to fragmentation of riparian habitats. Canopy nesters, including cavity-nesting species, responded positively in grazed habitats, while shrub-nesting species tended to decrease with grazing and recreational activities. Significant results of Poisson regression, for 17 of 30 species analyzed, suggested differential effects of land use, patch size, and/or the interaction between the two effects. Relative abundances of 11 species decreased with either grazing or recreation, whereas six species increased with these same activities. Five species (gray catbird, veery, yellow warbler, black-headed grosbeak, and American goldfinch) were unaffected by patch size in unmanaged areas but showed significant area effects (increases in probability of occurrence with cottonwood forest area) in grazed and/or recreation sites. Results of this study suggest that conservation of large patches is particularly important where riparian forests are managed for grazing and recreation. Apparently, some species need larger patches of breeding habitat in areas with these disturbances. In addition to evaluating the effects of local land-use practices on habitat relationships of breeding birds, the author examined the importance of landscape patterns to habitat use by birds. Among three spatial scales (landscape, macrohabitat, and microhabitat), landscape features were the most important and frequent predictors of distribution and abundance for most birds species and for predicting high species richness of native avifauna. Thus, surrounding landscape features should be a primary consideration for managing riparian habitats and selecting riparian reserve areas.

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ANIMAL EF: BIRDS, ELECTRONIC FILE - ZOOLOGY