Winter Bird Diversity and Community Structure in Relation to Shrub Cover and Invasive Exotic Natal Grass in Two Livestock Ranches in the Chihuahuan Desert, Mexico.

Simple Summary: Grasslands are one of the most threatened terrestrial biomes leading to a loss of grassland biodiversity, including birds. Two important factors contributing to the loss of grasslands and their birds are the expansion of woody vegetation and invasive exotic grasses into native grassland habitats. To be able to protect grassland bird communities, it is essential to know how they are affected by these two threats. In this study, we determined the wintering grassland bird diversity and community structure in two private livestock ranches in the Chihuahuan Desert, Mexico, and related this to vegetation measurements, such as grass cover and height, shrub cover and height, as well as the cover of the invasive exotic natal grass. We found that the amount of bare ground (no vegetation) negatively affected the grassland bird diversity on a local scale. We also found that shrub cover, grass height and natal grass cover affected the grassland bird community composition at the ranch level, indicating that shrub cover and natal grass appeared to negatively affect the presence of grassland specialist bird species in the bird community. The results, therefore, indicated that it is important to halt the invasion of shrubs and natal grass into grasslands because they alter the grassland bird community. Grasslands are one of the most threatened terrestrial biomes leading to a loss of grassland biodiversity, including birds. Here, we studied the wintering grassland bird diversity and community structure in two private livestock ranches in the Chihuahuan Desert, Mexico. We explored how bird communities are related to vegetation structure, including shrub cover and invasive exotic natal grass (Melinis repens), two drivers of grassland bird habitat degradation. We used Hill's numbers to estimate taxonomic species richness and diversity and related these metrics to vegetation covariables using linear models. We employed nonmetric dimensional scaling (NMDS) to explore the importance of vegetation covariates in structuring bird communities. We found that bird species diversity was significantly and negatively related to bare ground cover at a plot level. At the ranch level, shrub cover, grass height and natal grass were important in structuring avian communities, negatively affecting the presence and abundance of grassland specialist bird species. Our results indicated that shrub encroachment and invasive exotic natal grass cover may alter grassland bird communities and should, therefore, be considered in grassland bird conservation management. [ABSTRACT FROM AUTHOR]