Status

 There are two subspecies of Yellow-billed Cuckoo (Coccyzus americanus) recognized in the western hemisphere: C. a. occidentalis and C. a. americanus.  Their range historically extended from southern British Columbia to northern Mexico (Bent 1940).   Currently the only known populations of breeding Western Yellow-billed Cuckoos (Coccyzus americanus occidentalis) are in California, Arizona, and western New Mexico.

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Range and Distribution

Historically, Yellow-billed Cuckoos (Coccyzus americanus occidentalis) were common along river bottoms throughout their range (Gaines and Laymon 1984). Millions of hectares of riparian habitat were available along these waterways, but as human populations spread across the continent, much of this riparian habitat was lost to agriculture, livestock grazing pressure, and use of vegetation for fuel.  Up to perhaps ninety percent of the natural riparian ecosystems in the southwestern United States are currently gone (Ohmart and Anderson 1986).   In some states, such as California and Arizona, this loss may exceed 95% (Warner 1979), with muchof the remaining riparian areas endangered by human activities (Franzreb 1987; Almand and Krohn 1978) such as grazing pressure, lowered water tables, and pesticide use (Gaines 1974, Rosenberg et al. 1991).

With the loss of habitat, the overall range of the Yellow-billed Cuckoo contracted, and the last birds were sighted in British Columbia in 1920, in Washington in the 1930's, in Oregon in the 1940's, and in California north of the Sacramento Valley in the 1950's.   A recent survey of birds at Petrified Forest National Park in northeastern Arizona (Banks, van Riper and Rosenstock 2003) demonstrated that the Yellow-billed cuckoos no longer breed in that park.  A baseline inventory from 1975 to 1979 in the Lower Colorado Valley, compared to a study in 1986 showed a decline in populations numbers of 93% (Rosenberg et al. 1991).  Other documentation of declines are substantiated by Gaines and Layman 1984 and Laymon and Halterman (1987.  A number of other  avian species have also been impacted by this loss of riparian habitat, such as Bell's Vireo (Vireo bellii) and Willow Flycatcher (Empidonax trailii), which have both been extirpated from large segments of their historical ranges (Goldwasser et al. 1980).

According to most geneticists, 50 individuals is considered to be the minimum viable vertebrate population able to withstand such effects as demographic and environmental pressures, natural disasters and genetic stochasticity (Shaffer 1981).  In 1977 it was estimated that only a total of 205-214 pairs were extant, with more than half of these along the lower Colorado River and 35-60 pairs along the Sacramento River (Gains and Laymon 1984).  In 1985 the U. S. Fish and Wildlife Service proposed a management plan for the Yellow-billed Cuckoo in order to maintain a viable population "distributed throughout its historical breeding range" (USFWS 1985), and in 1987 the California Department of Fish and Game upgraded the status of the subspecies from rare to endangered. The USGS and Arizona Game and Fish has investigated the current populations in Arizona and these results will be published at this web site and as reports become available.  Visit our Data Pages to see the latest survey results, either in tabular or geospatial form.