The western yellow-billed cuckoo, once common along the streams and rivers of the American West, is now a candidate for protection under the Endangered Species Act. Most of the remaining breeding pairs are found in Arizona, California, and New Mexico. Research to understand the cuckoos' habitat needs by U.S. Geological Survey (USGS) and Northern Arizona University scientists has shown that cuckoos in Arizona prefer breeding habitat dominated by native tree species, especially cottonwood-willow habitat bordered by mesquite bosque habitat. This research also revealed that the size of habitat patches matters - breeding cuckoos were found only in large, continuous areas of riparian habitat. These findings and the development of spatially explicit habitat models by USGS scientists will help resource managers conserve and manage riparian habitats needed to ensure the survival of the western yellow-billed cuckoo.