Using Vegetation Guilds to Predict Bird Habitat Characteristics in Riparian Areas

Within arid regions riparian forests support high bird diversity compared to surrounding uplands. In these same regions, water demands for agriculture, urbanization, and recreation have altered the structure and composition of riparian forests and degraded bird habitat. Along rivers, plants with similar responses to flood disturbance and water availability can be grouped into functional guilds using traits. The use of plant guilds can mechanistically link bird distributions to traits such as canopy height, specific leaf area, and growth form. We demonstrate that bird species richness, abundance, and diversity are related to the heterogeneity of vegetation structure and plant guilds along a perennial river in the southwestern U.S. High-quality habitat can be explained by canopy cover, foliage height diversity, and foliage cover in the understory. The tall tree guild (dominated by Salix gooddingii) was the strongest predictor of bird habitat followed by drought tolerant shrubs (dominated by Prosopis velutina) demonstrating that riparian shrublands should be considered for conservation alongside gallery forests. Projected changes in flow regimes may result in homogenization of riparian vegetation and reduce habitat quality for migratory and breeding land birds. Practitioners can use developed methods to group vegetation by guilds to focus bird conservation efforts in arid ecosystems.