The lower Gila River Valley of southwestern New Mexico contains some of the finest riparian habitat and most diverse wildlife associations in the entire lower Colorado River drainage (Zimmerman 1970, 1975; Hubbard 1971; Johnson et al. 1974). Over two-thirds of New Mexico’s total of 449 bird species are known from the valley (Zimmerman 1975; Hubbard 1977).
In addition, the New Mexico portion of the Gila River Valley contains the greatest diversity of raptors in the lower Colorado River drainage, as well as the largest number of endangered, threatened, and peripheral bird species(Johnson et al. 1974).