Effect of Hydrologic, Geomorphic, and Vegetative Conditions on Avian Communities in The Middle Rio Grande of New Mexico

Abstract

We evaluated relationships among hydrogeomorphology, vegetation structure and composition, and avian communities among three subreaches of the San Acacia Reach of the Middle Rio Grande (MRG) River of New Mexico. The subreaches varied in degradation, with Subreach 1 being severely entrenched and hydrologically disconnected, Subreach 2 being the least impacted, and Subreach 3 being intermediately disturbed. Avian point count and habitat surveys were conducted to determine avian community structure and abundance, geomorphic feature, surface flooding, and vegetation structure and composition. Ground-nesting birds and low shrub-nesting birds were insensitive to hydrogeomorphic changes as they do not rely on native understory but can use exotic understory or woody debris. In contrast, canopy-nesting birds required native overstory; therefore, they were sensitive to hydrogeomorphic changes as native overstory species require surface floods to germinate and establish. Additionally, native overstory did not vary as expected as the moderately impacted subreach, Subreach 3, had more native overstory (x¯ = 30.04%, SE = ±4.57) than the least disturbed subreach, Subreach 2 (x¯ = 11.20%, SE = ±1.96). These findings were a result of temporal asynchrony between hydrogeomorphic conditions and overstory composition. No subreach is unaltered and all have been affected by the hydrologic and geomorphic changes on the MRG.