We studied the effects of cutting Ashe juniper (Juniperus ashei Bucholz) woodlands on populations of small mammals at Friedrich Wilderness Park, north of San Antonio, Texas. Three patches of juniper ranging from 1.8 ha to 2.4 ha were cut to provide habitat for endangered black-capped vireos (Vireo atricapillus Woodhouse). We trapped small mammals along transects placed in the treated patches and in untreated areas of the park from October 1995 to May 1996 and again from October 1996 to March 1997. Three species of small mammals were trapped, but Peromyscus pectoralis Osgood (white-ankled mouse) was the most common species captured. Peromyscus pectoralis was more abundant in the treated patches in which the juniper had been removed. Trapping success in the three treated areas was consistently higher (average of 12%) than in the untreated Ashe juniper woodlands (average of 3%). Mice that colonized treated patches survived longer than mice in control areas. Each year the number of P. pectoralis increased during the winter and spring, with juveniles accounting for up to 32% of captures. The management of habitat for an endangered species, such as the black-capped vireo, enhanced the biodiversity of small mammals in this study.