Status Report for the Yellow-billed Cuckoo (May 2017)

The western Yellow-billed Cuckoo (Coccyzus americanus) was designated as a distinct population segment by the U.S. Fish and Wildlife Service in 2013 and was classified as a threatened species under the federal Endangered Species Act in 2014. The population, which is migratory and overwinters in South America, formerly nested across much of the western United States, southern British Columbia, and northwestern Mexico. In the western U.S., nesting is strongly associated with large (usually exceeding 40 ha in size), wide (over 100 m) patches of low to mid-elevation riparian habitat dominated by cottonwoods, willows, and a mix of other species. Historically, Washington birds also nested in brushy habitats and fir forests. Most western birds arrive at their breeding range from early to mid-June and depart from late August to mid-September. Unlike most Old World cuckoos, Yellow-billed Cuckoos usually rear their own broods and rarely parasitize the nests of other birds. One brood is produced in most years, but two or even three broods may be reared in years with abundant prey resources. Diet consists mostly of large insects, especially caterpillars.

The population size and breeding range of western Yellow-billed Cuckoos have greatly declined during the past century, with only 680 to 1,025 breeding pairs estimated to remain. Historical records suggest that the species once nested in at least six areas of western Washington: (1) the vicinity of Bellingham and Marietta in Whatcom County; (2) the Mount Vernon area in Skagit County; (3) the area around Lake Washington and Seattle in King County; (4) the Tacoma area in Pierce County; (5) the vicinity of Grays Harbor in Grays Harbor County; and (6) the lower Columbia River in the vicinity of Vancouver and Ridgefield in Clark County. With the exception of the lower Columbia River, abundance in each of these areas was probably small. Breeding in the state was last fully confirmed in 1923, but likely continued until at least the early 1940s.

Just 20 sightings of Yellow-billed Cuckoos have been documented in Washington since the 1950s, with 19 occurring from 1974 to 2016 at an average rate of one sighting every 2.3 years. Sixteen of the 20 records occurred in eastern Washington. All or nearly all of the birds recorded since the 1950s were very likely non-breeding vagrants or migrants, indicating that cuckoos are now functionally extirpated in the state. Nevertheless, due to a lack of surveys for the species and the presence of small areas of habitat in Washington, the possibility exists that this species may occasionally breed in the state and that these rare breeders are yet to be discovered.

The greatest threat to western Yellow-billed Cuckoos, including those that bred in Washington, has been the loss or degradation of riparian habitats caused by dam construction, flood control practices, commercial and residential development, changes in farming and ranching practices, and nonnative plant invasions. Agricultural pesticide use, which may affect prey abundance as well as the birds' health, is a potential additional threat.

For these reasons and because the western DPS of the species is federally classified as threatened under the Endangered Species Act, it is recommended that the Yellow-billed Cuckoo be listed as a state endangered species in Washington.