Impacts Of Woody Plant Removal On Wintering Grassland Bird Communities And Habitat Characteristics in the Trans-Pecos, Texas

Emily Card, Mieke Titulaer, Carlos E. Gonzalez, and Louis A. Harveson

Grasslands are one of the world’s most imperiled ecosystems, having declined up to 98% in some areas of North America since the settlement of Euro-Americans. Consequently, populations of grassland birds have declined consistently and at higher rates than any other group of birds on the continent. More than 700 million grassland birds that breed in North America have been lost since 1970 (i.e., a 53% decline). This significant decline over the past half-century is primarily attributed to the loss of suitable habitat, both on the breeding and wintering grounds. Notable drivers of habitat degradation include agriculture expansion, urbanization, livestock overgrazing, energy development, desertification, and non-native species invasion.

Approximately 90% of migratory grassland bird species that breed on North America’s Great Plains spend the winter in the Chihuahuan Desert, making this region imperative for suitable habitat. However, the encroachment of woody plants into grasslands in this region degrades and changes suitable habitat into desert shrublands, contributing to the decline of grassland bird species. Woody plant invasion is caused by various factors, including overgrazing by livestock, periodic droughts, fire management, and changes in soil properties.

To evaluate how grassland birds respond to habitat restoration efforts, we will conduct bird and vegetation surveys on a private ranch in the Marfa grasslands. In the summer of 2019 this ranch was treated with an aerial herbicide spray, making it a suitable site for this study. We will collect data during the winters of 2021 and 2022, expanding on survey data previously collected in 2019 and 2020. The objectives of this project are to 1) estimate grassland bird abundance in grassland plots, herbicide-treated plots, and untreated shrubland plots, and 2) assess how treatment for woody plant removal influences habitat characteristics and the structure of wintering bird communities. Results of this study will help us understand if using herbicide to remove woody plants is an effective way to restore grassland ecosystems and threatened grassland bird groups in the Chihuahuan Desert.

Funding sources: National Fish and Wildlife Foundation and the Borderlands Research Institute.