Natural area managers in regions of the semi-arid west, particularly on the Colorado Plateau, are presently dealing with expanding pinyon (Pinus spp. Engelm.) — juniper (Juniperus spp. Engelm.) woodlands on rangelands. Increased equipment costs associated with ‘chaining’, and dangers associated with prescribed fires, have resulted in more instances where mechanical thinning of woodlands is being used. Our 2005 to 2006 study within Grand Staircase Escalante National Monument, Utah, examined responses of breeding birds to the mechanical reduction of pinyon-juniper woodlands within a randomized 4-block design that incorporated 11 control and nine treatment bird count stations. We surveyed birds within 3.1-ha bird-count stations (n = 20) prior to, and following, pinyon-juniper mechanical reduction treatments. Thinning in April 2006 removed a mean of 92% ( 6.4% SE) of live trees from treatment blocks. The avian guild most greatly influenced by mechanical thinning included pinyon-juniper obligate species. Species eliminated following mechanical thinning were Gray Vireo (Vireo vicinior) and Brown-headed Cowbird (Molothrus ater), while Chipping Sparrow (Spizella passerine) numbers were significantly reduced. Birds in the shrub-nesting guild, including the sagebrush specialist Brewer's Sparrow (Spizella breweri), and habitat generalists such as the Bushtit (Psaltriparius minimus), increased in relative abundance following treatment. We conclude that mechanical thinning within the Intermountain West has the potential for natural area managers to design treatments that can influence numbers of both pinyon-juniper and sagebrush (Artemisia tridentata Nutt.) steppe avian species.