Due to significant population declines during the 20th century, the Western Yellow-billed Cuckoo is considered an imperiled species west of the Continental Divide and is a candidate for listing under the Endangered Species Act (Listing Category 3). The Colorado Division of Wildlife’s Comprehensive Wildlife Conservation Strategy lists it as a Species in Greatest Need of Conservation (Tier 1).

In the 1950s and 1960s cuckoos were found breeding annually in western Colorado near Grand Junction (Righter et al. 2004). They were regularly detected as recently as the early 1980s along the Uncompahgre and Gunnison Rivers near Delta (Rich Levad, pers. comm.); however, during the Colorado Breeding Bird Atlas (1987-1994), breeding was confirmed in only one location on the Western Slope – on the Yampa River in Routt County (Colorado Bird Atlas Partnership 1998). Since 2003 only two locations in the Western Yellow-billed Cuckoo’s range have been consistently occupied. One is along the Conejos River in the San Luis Valley of south-central Colorado (Banks and Lucero 2004) where breeding is suspected but has not been confirmed. The other location is along the North Fork of the Gunnison River in west-central Colorado where breeding was confirmed in 2008.

Since 2008 Rocky Mountain Bird Observatory, with funding from the Bureau of Land Management, Colorado Division of Wildlife, and U.S. Fish and Wildlife Service, has conducted surveys to determine areas occupied by Western Yellow-billed Cuckoos in western Colorado.

This project employs site-occupancy surveys using call-playback methodology in which a recording of a Yellow-billed Cuckoo call is played at each survey station to lure cuckoos closer to the observer so that they can be seen and to encourage a vocal response (following Halterman 1991). Surveys have been conducted between June 15 and August 15 following a protocol developed by the Western Yellow-billed Cuckoo Working Group.

In 2008 RMBO surveys detected cuckoos at six locations in the North Fork valley (Delta County) and at three other locations in western Colorado (in Moffat and Montrose counties). There were also incidental sightings of cuckoos in four locations in the North Fork valley. An exciting find during the 2008 surveys was a cuckoo nest with two nestlings in the North Fork valley near Hotchkiss on July 21. Prior to this observation, Yellow-billed Cuckoos had not been confirmed breeding in western Colorado since 1998. One nestling was again seen after fledging from the nest.

In 2009 and 2010, surveys of western Colorado riparian areas yielded no detections of Yellow-billed Cuckoos. However, incidental detections continue to be recorded along the Conejos and North Fork of the Gunnison rivers at what seem to be the last two strongholds for the species. RMBO’s surveys demonstrate that the species is rare in western Colorado and perhaps on the brink of being extirpated as a breeder. RMBO will continue searching for Yellow-billed Cuckoos in western Colorado and may expand surveys into western Wyoming in 2011.