Relationships among Birds, Willows, and Native Ungulates in and around Northern Yellowstone National Park

A threshold of tolerance for browsing exists among bird species in Yellowstone's riparian zones, beyond which both bird density and species richness decline significantly. This study, conducted across eight willow stands with varying levels of elk and moose browsing (ranging from 3.5% to 100% severely browsed willows), found that only two sites supported all five focal bird species (Common Yellowthroat, Lincoln's Sparrow, Warbling Vireo, Wilson's Warbler, and Yellow Warbler). The Lincoln's Sparrow was the only species present in all stands. Using data from 1989–1990, researchers measured bird densities and habitat structure variables, revealing that browsing intensity, shrub height heterogeneity, foliage density, and landscape factors (e.g., hydrology, adjacent community type) collectively shape bird assemblages. While browsing directly affects bird communities, predictive models incorporating broader ecological variables could improve accuracy.

Jackson, S. G. (1992). Relationships among Birds, Willows, and Native Ungulates in and around Northern Yellowstone National Park. Utah State University. https://doi.org/10.26076/2CC5-07AF