Home Range and Movement Patterns of Wintering Baird’s and Grasshopper Sparrows in the Marfa Grasslands, Texas

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

Grassland specialist bird species rely on pristine grassland habitats to reproduce in, access for resources, and find shelter. These species are also one of the most imperiled groups of birds in North America, having experienced steep and consistent declines over the past half-century. Since 1970, over 50% of all grassland bird species have been lost. The degradation and loss of grasslands across the continent have been cited as a primary factor contributing to this significant decline. Notable drivers of habitat degradation include agriculture expansion, urbanization, livestock overgrazing, energy development, fire suppression, woody plant encroachment, and non-native plant species invasion.

The Baird’s sparrow (Centronyx bairdii) and grasshopper sparrow (Ammodramus savannarum) are two grassland specialist species in North America that have declined approximately 2% and 2.5% per year, respectfully, between 1966 and 2015. Previous research has demonstrated that both species select areas with low shrub cover and dense grass during the breeding season. However, the ecology of Baird’s and grasshopper sparrows under changing environmental conditions on the wintering grounds remains relatively unknown. Radio telemetry is one method commonly employed by avian biologists to identify environmental factors that influence the survival rates of birds during their annual life cycles.

Therefore, to better understand the ecological requirements of wintering Baird’s and grasshopper sparrows in the Trans-Pecos, Texas, individuals of these species were captured and fitted with radio transmitters during the winters of 2016-2019 in the Marfa Grasslands. The objectives of this project are to 1) use the data collected by the radio transmitters to identify and define winter home ranges for Baird’s and grasshopper sparrows, and 2) assess winter movement and dispersal patterns of these sparrow species. This information will help us understand how Baird’s and grasshopper sparrows utilize available habitat and respond to changing environmental conditions in the desert grasslands of the Trans-Pecos.

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