We measured and compared the dimensions, height, and orientation of Gila Woodpecker (Melanerpes uropygialis) and Northern Flicker (Colaptes auratus) nest cavities, and compared saguaros used for nest sites to the saguaros available for both species. Gila Woodpecker nest cavities had smaller entrances, were shallower in the vertical plane of the saguaro, and were deeper in the horizontal plane of the saguaro than Northern Flicker nest cavities. These data can be used to determine whether secondary cavity-nesting species are using Gila Woodpecker cavities, Northern Flicker cavities, or both. The mean height of nest cavities did not differ between species, and the orientation of nest cavities was random for both species. Although saguaro selection differed between the species, both selected the largest saguaros for nest sites. No nests of either species were found in saguaros <5 m tall. The continued existence of the saguaro cavity-nesting community is dependent upon the survival of large saguaros and adequate saguaro reproduction, despite human development of their desert habitat.
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