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

Abstract

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.