Comparative Habitat Use of Wintering American Kestrels and Loggerhead Shrikes Along South Texas Roadways

Falco sparverius (American Kestrel) and Lanius ludovicianus (Loggerhead Shrike) have undergone major population declines, which may be partially due to habitat changes on their wintering grounds. The objectives of this study were to compare quantitative habitat metrics and landcover data at sites used by American Kestrels and Loggerhead Shrikes during the winter. We conducted this study by observing individuals of both species along private and public roads across 8 counties in South Texas and recording GPS coordinates and various habitat characteristics at each location. We calculated woody canopy cover by digitizing all woody cover within 100 m of the sighting locations and at random points, and obtained landcover data from the National Land Cover Database (NLCD) for 2001 and 2011. Female American Kestrels were associated with shorter herbaceous height (median = 7.4 cm) than male American Kestrels (16.4 cm) or Loggerhead Shrikes (13.6 cm). Woody canopy cover was lower around sites used by female American Kestrels (q(0)(.9) = 1.9%), compared to sites used by male American Kestrels (q(0.9) = 17.8%), Loggerhead Shrikes (q(0)(.9) = 21.3%), or at random points (q(0)(.9) = 51.6%). Although cultivated crops were the most common cover type within 100-m radius buffers of each species group, this cover type was more abundant (73.2% +/- 1.5) in sites used by female American Kestrels than sites used by male American Kestrels (47.7% +/- 4.1) or Loggerhead Shrikes (41.1% +/- 2.7). In contrast, sites used by female American Kestrel had lower amounts of pasture/hay, grassland/herbaceous, and shrub/scrub types compared to those used by male American Kestrels or Loggerhead Shrikes. Two of the most important cover classes for American Kestrels and Loggerhead Shrikes, cultivated crops and pasture/hay, still comprised 26.0% (481,882 ha) and 22.3% (413,396 ha) of these 8 South Texas counties in 2011, but had decreased by 0.77% and 0.84% since 2001. Medium- and high-intensity development has increased, for a total of 3360 ha (15.49% change), over the same timeframe. Slowing the loss of these favorable open-cover habitat types should be a priority for the conservation of American Kestrels and Loggerhead Shrikes in South Texas.