Photo taken by Joss Perez

Overwinter Habitat Use of Baird’s and Grasshopper Sparrows in the Marfa Grasslands, Texas

Alex Chavez-Trevino, Mieke Titulaer, Carlos Gonzalez, Louis A. Harveson, and Maureen Correll (Bird Conservancy of the Rockies)

Grassland-obligate bird species (GOBS) are specialized birds that live in pristine grasslands of North America. Most of these species breed in the Northern Great Plains and spend the winter in the Chihuahuan Desert. Unfortunately, these bird species are declining dramatically. Around 54% of all grassland birds have vanished only in the past 50 years. They are considered the fastest declining group of birds in North America. These declines are attributed to many causes, but habitat degradation is one of the main reasons for grassland bird decline. The decrease of grass cover and the increase of shrubs cover due to anthropogenic activities such as unsustainable grazin, fire suppression and extraction of burrowing mammals limit the survival of grassland-obligated bird species. Habitat restoration may help mitigate habitat change by bringing back the grasslands and the birds that rely on this habitat.

My project evaluates the early effect of a chemical treatment for shrub removal in a private property in West Texas. We used a paired treatment-control design to conduct bird surveys during winters in shrub invaded areas before and after the treatment, and control areas containing open pristine grassland. My study sites are located in the Marfa and Marathon grasslands in the Trans-Pecos area of Texas. My objectives are to 1) compare bird populations between the two habitat types, and 2) start a long-term bird monitoring program to evaluate changes in bird populations on restored sites.

During the winters of 2019 and 2020, we performed at least 54 (875 yard) line transects per site from the first of January to the end of February. We have conducted over 500 line transects, surveyed 240 miles of line transects and detected over 20,000 birds from 66 different species. Early results show a greater density of grassland obligate sparrows such as Baird’s sparrows, Horned Larks and Easter Medaowlarks in the grassland control sites. Interestingly, we found a reduction of about 60% on Black-throated sparrows and 30% of Eastern Meadowlarks in the treated sites after the spray. In the long term, we expect an increase of grassland bird abundance in the restored sites once the treated shrubs are completely removed from the plots.

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