U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3091

2009

In cooperation with Northern Arizona University

Understanding the Habitat Needs of the Declining 

Western Yellow-Billed Cuckoo

yellow-billed cuckoo, U.S. Geological Survey 

(USGS) and Northern Arizona University 

scientists have been studying this bird along 

the lower Colorado River in Arizona and 

California. Although the lower Colorado 

River represents some of the best remaining cuckoo habitat in that region, a previous 

study estimated that cuckoo populations there 

declined by 93% between 1976 and 1986. By 

1998, USGS scientist were unable to locate 

any yellow-billed cuckoo pairs in the parts of 

California west of the Colorado River that had 

been occupied in 1976 and 1977.

The decline of the western yellow-billed 

cuckoo coincides with the growth of human 

populations in the West and the loss of riparian habitat (habitat near a waterway) resulting 

from increased development, agriculture, and 

dam building. In Arizona, it has been estimated that during the past 300 years riparian 

ecosystems have declined from approximately 5% of the State’s landmass to 1%.

In 2001, as the result of habitat loss, the 

U.S. Fish and Wildlife Service found that the 

western yellow-billed cuckoo (that is, populations west of the crest of the Rocky Mountains) represents a distinct population segment 

and warrants protection under the Endangered 

Species Act. It was determined that the western yellow-billed cuckoo should be listed as 

“threatened,” but this action was precluded 

by other higher priority listing actions. As of 

2009, the western yellow-billed cuckoo is still 

a candidate for listing under the act.

Research Findings

In 1998 and 1999, USGS scientists 

worked with the Arizona Game and Fish 

Department to locate cuckoo populations 

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.

The western yellow-billed cuckoo 

(Coccyzus americanus occidentalis) is a shy 

neotropical migrant bird; its loud “ka, ka, ka, 

ka, ka, kow, kow, kow” call is often the only 

evidence that this reclusive bird is present. 

Traveling from their winter homes in South 

America, the birds arrive in the Western 

United States to breed from early June to late 

August in vegetated areas along rivers and 

streams. Once common between the Rocky 

Mountains and the Pacific Ocean and from 

lower British Columbia, Canada, south to 

northern Mexico, western cuckoos have now 

disappeared from the Pacific Northwest and 

Canada, and only a few pairs still breed in 

Utah, Idaho, Colorado, and Nevada. Most 

breeding occurs in isolated areas along rivers 

in Arizona, California, and New Mexico.

Because relatively little is known about 

the life history and habitat needs of the western 

An adult western yellow-billed cuckoo (Coccyzus americanus occidentalis), a candidate for 

protection under the Endangered Species Act. U.S. Geological Survey scientists have undertaken 

research to understand the bird’s specific habitat needs. (Photograph © Bob Steele/VIREO.)
For more information contact:

U.S. Geological Survey

Southwest Biological Science Center

Colorado Plateau Research Station

Flagstaff, Arizona 

928-523-7764 or 

mjjohnson@usgs.gov

This Fact Sheet and any updates to it are available

online at http://pubs.usgs.gov/fs/2009/3091/

throughout Arizona. Cuckoos were found 

primarily along the Agua Fria, San Pedro, and 

Verde Rivers, Cienega and Sonoita Creeks, 

and the Bill Williams River, a tributary to the 

lower Colorado River. Additional surveys done 

from 2005 to 2007 indicated that 85% of the 

cuckoos detected in the lower Colorado River 

Basin were found at Bill Williams National 

Wildlife Refuge, Arizona (Johnson and others, 

2008), where the highest quality cuckoo habitat 

in the region still exists.

The breeding cuckoos found along the 

Bill Williams River were nesting in riparian 

habitat dominated by native tree species, particularly cottonwoods and willows; cuckoos did 

not breed in small, isolated patches or in areas 

dominated by exotic vegetation such as tamarisk. In addition to patch size, the vegetation 

that surrounds a patch may influence whether 

cuckoos use a site. Additional research conducted in central Arizona showed that cuckoos 

were most often found in cottonwood-willow 

habitat bordered by mesquite bosque habitats 

(Holmes and others, 2008).

Scientists also found that sites occupied 

by cuckoos generally had taller trees, thicker 

cover in the upper and middle layers of the 

canopy, and sparser shrub layers than unoccupied sites. Unoccupied sites consistently 

had very little canopy and higher densities 

of small trees, mostly nonnative tamarisk. 

Cuckoos may prefer riparian areas that are 

dominated by native species with a multistoried structure and high, dense canopies for 

nesting and an open understory for foraging.

Scientists have hypothesized that the 

cuckoo is restricted to moist river bottoms to 

meet humidity levels required for successful 

breeding. To examine this idea, scientists measured microclimate variables—temperature and 

relative humidity—along the lower Colorado 

River at occupied and unoccupied sites. Sites 

occupied by cuckoos were consistently cooler 

during the day and more humid during both 

day and night than unoccupied sites.

Changing environmental factors also 

affect cuckoo habitat—sometimes rapidly. 

In 2006, surveys conducted in Lake Mead 

National Recreation Area, Arizona and 

Nevada, detected many pairs of breeding 

cuckoos in the area where the Colorado River 

flows into the lake, an area known as the Lake 

Mead delta. A year later, in 2007, scientists 

detected no cuckoos in the delta. Many of the 

native trees where cuckoos bred in 2006 had 

died or were dying in 2007. The native tree 

die off occurred during an ongoing drought, 

which dropped the water level of Lake Mead 

by approximately 15 feet from 2006 to 2007. 

Dead trees, or snags, increased from 14 to 

46% of the delta’s entire woody vegetation 

from 2006 to 2007.

Identifying High-Quality 

Cuckoo Habitat

As the changes at Lake Mead highlight, 

riparian ecosystems are dynamic and can 

change rapidly. USGS scientists are developing spatially explicit habitat models to examine 

how landscape-scale habitat variables affect 

cuckoo distribution. Spatially explicit habitat 

suitability models provide powerful tools for 

identifying habitat requirements of target species at multiple spatial scales. Such models not 

only help resource managers understand the 

ecology of a target species like the cuckoo, but 

also provide managers with site-specific information in the form of geographic information 

system (GIS) habitat maps. These models can 

identify the relative importance of individual 

variables (or combination of variables) in 

influencing the distribution of a species.

Understanding the habitat needs of 

the shy western yellow-billed cuckoo is an 

important step toward conserving this species. 

This USGS research demonstrates the key role 

that large, continuous areas of native riparian 

trees play in the cuckoo’s selection of breeding 

habitat. These findings and the development 

of spatially explicit habitat models can help 

resource managers to conserve, manage, and 

restore the riparian habitats needed to ensure 

the survival of the disappearing western 

yellow-billed cuckoo.

Matthew J. Johnson

References

Holmes, J.A., Johnson, M.J., and Calvo, C., 

2008, Yellow billed cuckoo distribution, 

habitat use and breeding ecology in the Verde 

Watershed of Arizona, 2003–2004; final 

report: Phoenix, Ariz., Arizona Game and 

Fish Heritage Program, 174 p.

Johnson, M.J., Durst, S.L., Calvo, C.M., 

Stewart, L., Sogge, M.K., Bland, G., and 

Arundel, T., 2008, Yellow-billed cuckoo distribution, abundance, and habitat use along 

the lower Colorado River and its tributaries, 

2007 annual report: U.S. Geological Survey 

Open-File Report 2008–1177, 268 p.

Habitat used by breeding 

western yellow-billed 

cuckoos along the Bill 

Williams River in Arizona. 

The birds nest almost 

exclusively near water in 

large, continuous patches 

of native woodlands with 

cottonwoods and willows. 

(USGS photograph by 

Matthew J. Johnson.)

Historical and current distributions of the 

western yellow-billed cuckoo.

Historical range

Current populations

P

acific Ocean

CA

NV

UT

AZ

OR ID

NM

WY

MT

CO

TX

WA

0 300 MI N

0 300 KM