The habitat ecology of masked bobwhites (Colinus virginianus ridgwayi) is poorly understood, which hampers recovery efforts for this endangered bird. During 1994-96, we analyzed the habitat ecology of masked bobwhites in Sonora, Mexico, and Arizona, and compared these findings with the habitat ecology of Texas bobwhites (C. v. texanus) in southern Texas. Mean values for the quantity of low screening cover (<50 cm aboveground), operative temperature (??C), and exposure to aerial predators were relatively constant across regions (CV <14.2%), indicating these variables are important in adaptive habitat-use decisions by bobwhites. Bobwhites exhibited preference in all regions for higher canopy coverage of woody vegetation, lower exposure to aerial predators, and lower operative temperatures in comparison with randomly available conditions. The major habitat deficiencies for masked bobwhites were lack of woody and herbaceous cover, which led to high exposure to aerial predators in Sonora and Arizona. High operative temperatures at quail level were associated with the loss of ???24% of potential habitat space-time in Texas, Sonora, and Arizona. Management to improve habitat for masked bobwhites includes any practice that increases canopy coverage of woody vegetation, and height and coverage of herbaceous vegetation.