Breeding and wintering bird occurence in Texas rangelands with special reference to woody plant encroachment

Abstract

Within the past 150 years, rangeland vegetation in Texas has undergone a large-scale conversion from grasslands and savannas to shrublands and woodlands. Concurrently, grassland bird species have shown more declining trends than any other avian species group in North America. However, in Texas, many bird species and an endangered species utilize the encroaching woody plants. I studied breeding and wintering species within 2 watersheds on the Edwards Plateau. Breeding birds were surveyed with 498 point counts and wintering birds with 280 line transects across the range of vegetation conditions within the watersheds during 2001 and 2002. Grassland-associated species had a negative association with juniper in both watersheds, but associations with mesquite differed by species. Birds within the shrubland and woodland-associated guilds also had mixed associations with juniper and mesquite that were species specific. The bird assemblages, encroaching woody species, and vegetation characteristics of the 2 watersheds were different. Therefore, management recommendations need to be addressed at the watershed level.