Project Spotlight: Baird’s and Grasshopper Sparrows in the Marfa Grasslands

Borderlands Research Institute

A Baird’s sparrow perches atop a mesquite in the Marfa Grasslands of West Texas. Baird’s sparrows spend their winters here in the Chihuahuan Desert and are one of the grassland-obligate species whose populations are in steep decline.

The grassland ecosystem is one of the most threatened ecosystems globally, with only 20% of its historical range left in the world. Because of this, grassland birds have lost approximately 70-80% of their total population since 1966. As key indicators of grassland health and integrity, these birds are ecologically significant and merit further study.

Although habitat alteration on their wintering range has been acknowledged as a potential cause affecting winter survival and driving population declines, this key area remains poorly explored. With partners from Texas Parks and Wildlife Department, Bird Conservancy of the Rockies, and the Dixon Water Foundation, BRI has been studying two grassland-obligate bird species, Baird’s sparrow and grasshopper sparrow, to better understand their ecological requirements during the winter. Using mist nets, we captured birds each winter from 2016-2019, placed radio transmitters on them to track them daily, and documented vegetation composition throughout the study site to evaluate habitat conditions.

Preliminary results indicate that both species select for areas with low shrub cover and dense, tall grass, on which they depend for food and cover. We are also finding that Baird’s sparrow habitat requirements are more restricted; in addition to selecting for grass density and height, this species appears to be more negatively affected by the presence of tall shrubs, forbs, and tumbleweed compared to grasshopper sparrow. Such information on habitat requirements is key to better managing the winter habitat for the conservation of these and other declining grassland bird species.