Woody plant encroachment reduces density of most grassland specialists in a desert grassland but has limited influence on nest survival.

This article investigates the effects of woody plant encroachment (WPE) by Prosopis (mesquite) on breeding bird communities in desert grasslands of southeastern Arizona, USA. Surveying 140 plots with 0–37% woody cover from 2013 to 2015, the study found that densities of obligate grassland specialist birds declined substantially—by up to 75%—as woody cover increased, particularly when tree cover exceeded 15%, while facultative grassland species and non-grassland species increased or peaked at intermediate woody cover levels. Nest placement differed among groups, with obligate species nesting farther from woody plants, but WPE had limited and inconsistent effects on nest survival, affecting only Grasshopper Sparrow (Ammodramus savannarum) negatively and Mourning Dove (Zenaida macroura) positively at certain spatial scales. The findings suggest that early-stage WPE (woody cover <10% and shrubs <2 m tall) has significant negative impacts on grassland obligates, indicating that conservation and restoration efforts should prioritize controlling woody plants before they mature and become more difficult to manage.