Thresholds in forest bird communities along woody vegetation gradients in the South American Dry Chaco

1. Worldwide, tropical savannas and dry forests are under increasing pressure from land use. The environmental impacts of agricultural expansion into these ecosystems have received much attention, yet subtler changes in natural vegetation remain severely understudied.
2. We explored how bird communities vary along gradients of woody vegetation in the South American Dry Chaco by combining high-resolution, satellite-based tree, shrub, and total woody cover with field data on the frequency of 82 bird species surveyed in 167 plots. We identified change points along woody cover gradients where the relative frequency of individual bird species dropped most strongly. Based on this, we identified forest indicator species and assessed evidence for community-level thresholds.
3. Most forest birds (71%) had clear change points in their frequencies along vegetation gradients, starting as high as 38% total woody cover. Many (41%) forest species declined drastically at woody cover levels of less th...