Breeding bird responses to juniper woodland expansion

In recent times, pinyon (Pinus spp.)-juniper (Juniperus spp,) woodlands hav e expanded into large portions of the Southwest historically occupied by gr assland vegetation. From 1997-1998, we studied responses of breeding birds to one-seed juniper (J. monosperma) woodland expansion at 2 grassland study areas in northern Arizona, We sampled breeding birds in 3 successional sta ges along a grassland-woodland gradient: un-invaded grassland, grassland un dergoing early stages of juniper establishment, and developing woodland, Sp ecies composition varied greatly among successional stages and was most dif ferent between endpoints of the gradient, Ground-nesting grassland species predominated in uninvaded grassland but declined dramatically as tree densi ty increased. Tree- and cavity-nesting species increased with tree density and were most abundant in developing woodland. Restoration of juniper-invad ed grasslands will benefit grassland-obligate birds and other wildlife.