Invasion by a native grass: implications of increased dominance of Heteropogon contortus (Tanglehead) for grassland birds

Heteropogon contortus (tanglehead) is a native grass that has recently spread and become dominant on clay loam soils of southern Texas, leading some land managers to suggest this plant has become invasive. We sought to quantify effects of H. contortus dominance on plant and grassland bird communities in summer and winter 2011-2012 and to determine if responses are similar between seasons. Presence and cover of most species of plants decreased with increased dominance of H. contortus, but structure was taller, denser, and more homogenous than areas with minimal to no H. contortus. Presence and density of Scissor-tailed Flycatcher and presence of Brown-headed Cowbird decreased with H. contortus, whereas presence or density of Mourning Dove, Cassin’s Sparrow, Lark Sparrow, and Eastern Meadowlark increased in summer. Responses of wintering grassland birds generally were negative, with a few species increasing in presence or density. Based on changes we observed in the plant community, H. contortus could be considered an invasive species. Further, we advocate a holistic approach to studying the effects of invasive plants on avifauna because birds have different habitat requirements within each season, resulting in season-specific responses