Female big free-tailed bats Nyctinomops macrotis have been captured over water in northern Arizona in high elevation (> 2,400 m) forests and low elevation (1,500 m) desert scrub vegetation. We hypothesized that roost sites were in vertical walls of cliffs that were up to 25 km away from capture sites given the flight capability of these bats. During summer 2005 we captured eight females over ponds and attached radio transmitters to locate day roosts. We also identified locations used during nightly movements from 1 to 6 nights of radio tracking. We found three day roosts for seven bats; average distance (± SE) from a capture site to a roost was 12.1 ± 3.0 km. Roosts were small maternity colonies used by ≥ four N. macrotis in cracks or crevices in upper portions of vertical cliffs and faced south or southeast. Average dimensions for ponds where we found N. macrotis were 24 × 46 m, larger than the average pond size (14 × 19 m) where we did not capture this species. We identified 73 night locations for five N. macrotis and for one individual with 32 night locations calculated a 95% activity area (minimum convex polygon method) of 29,590 ha. Straight line distance between successive locations averaged 5.1 ± 0.8 km. Maximum distance detected from roost averaged 25.3 ± 4.9 km. We conservatively estimated a maximum flight speed of 61 km per hour. Most locations were in desert scrub vegetation but three bats moved to higher elevations, using pinyon-juniper (Pinus edulis-Juniperus spp.) woodland and ponderosa pine (Pinus ponderosa) forest. The maternity roosts we located for N. macrotis were remote, difficult to access, and within protected areas (national parks) in northern Arizona; however, foraging areas and ponds used for drinking are managed by different public or private agencies. These features are not as well protected and could be critically important in this arid environment.