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Status: Population size: 2.3 million Photo by George Jameson.

Curve-billed Thrasher
(Toxostoma curvirostre)

This species was on the 2002 WatchList, but is not on the 2007 WatchList. Please refer to http://web1.audubon.org/science/species/watchlist/techReport.php for information on the 2007 WatchList.

The Curve-billed Thrasher ranges throughout the arid southwestern United States and into northern and central Mexico. A long-term decline in U.S. populations has been documented and is likely to be the result of losses in breeding habitat to development and agriculture, especially in the areas where it is most abundant—the south Texas brushlands and Sonoran Desert of Arizona.

Identification
The Curve-billed Thrasher is about the size of the American Robin but more slender. It has orange eyes, white throat, grayish-brown body, and thick legs. It also has a long, slender, black bill that is curved. The Curve-billed Thrasher makes an all-purpose double whistle, whit-wheet. No other Toxostoma thrasher with an overlapping range makes this sound. In the eastern portion of the range it usually shows a lighter breast that adds contrast to its spots.

Distribution and Population Trends
A bird of the southwestern U.S. and Mexico, the Curve-billed Thrasher’s northern range extends from Arizona’s Sonoran Desert east across New Mexico to the western half of Texas and barely making into the corners of Colorado, Kansas, and the panhandle of Oklahoma. Range extends south through southern Mexico. A number of subspecies have been described but these can be broadly defined as an eastern group (T.c. curvirostre) and a western group (T.c. palmeri). Breeding Bird Survey trend analyses show a significant annual decline of 2.3% per year in the U.S. portion of thw Curve-billed Thrasher’s range from 1966-2001. Preliminary analyses of Christmas Bird Count data show a similar long-tern decline.

Ecology
Eastern populations are most dense in the south Texas brushland habitat. This species forages in open habitat and nests in woodland edges (for example, pinyon and oak) and exposed shrubs (including yucca), and is also found in thickets and thornscrub that abut woodlands. In Mexico, it lives in open and semiopen dry habitats, dotted with shrubs and cacti.

Western populations are most dense in the Sonoran desert. This bird lives in thornscrub, saguaro-palo verde communities, and towns. As long as cholla cactus is around, it will also live in creosote bush and grassland habitats. In the Sonoran desert of Mexico, the Curve-billed Thrasher is found in thornscrub and brushy forest edges.

The Curve-billed Thrasher forages by probing the leaf litter with its long, curved bill and digging holes. It eats mostly seeds and insects, but berries and cacti fruits are acceptable when available. A ground lover, the thrasher flies in a quick and jerky fashion from bush to bush. As long as both members stay in the area, couples appear to mate for life. Breeding usually takes places from May to mid-July. Both members of Curve-billed Thrasher pairs assist with nest construction. Pairs can have two broods in one season. They prefer to put their deep cup nests in Cholla cactus but will settle for a number of spiny shrubs.

Threats
The Curve-billed Thrasher has lost a considerable portion of its south Texas brushland habitat. And the expanding cities of Tucson and Phoenix are causing a rapid loss of habitat in Arizona. Meanwhile, buffel grass, an imported fire resistant grass, has been introduced to vast areas of former thrasher habitat in Sonora, Mexico and parts of the southwest, eliminating these areas as thrasher haunts.

Conservation
Although there has been little conservation work directly focused on the Curve-billed Thrasher, much work has been directed at protecting habitats in some areas where the species occurs. In Arizona, the Sonoran Desert Conservation Plan was developed under the leadership of Pima County with input from a multitude of groups including the Tucson Audubon Society and is likely to be beneficial to Curve-billed Thrasher populations.

In the south Texas portion of the species range there has been extensive work to begun restoring and protecting the remnant forests of the lower Rio Grande Valley of south Texas. The Lower Rio Grande Valley National Wildlife Refuge has been working since 1979 to protect habitat and restore native vegetation. The refuge encompassed more than 90,000 acres in more than 100 separate parcels as of 2002 and is expected to eventually include over 130,000 acres. Texas Parks and Wildlife is developing its World Birding Center in south Texas for launch in 2003 with the goal of engaging both local communities and visitors in state-of-the-art education, restoration and conservation projects, while offering new habitat areas to birdwatchers.

What Can You Do?
Audubon’s Important Bird Areas program is a vital tool for the conservation of Curve-billed Thrashers as well as other species. To learn more about the Important Bird Area programs in states with Curve-billed Thrasher populations, and how you can help, visit: http://www.audubon.org/bird/iba/.

Support local land trusts, government agencies, and other organizations working to preserve Curve-billed Thrasher habitats in you area. Contact your state Important Bird Areas coordinator (http://www.audubon.org/bird/iba/state_coords.html) to find out if there are sites in your area important for Curve-billed Thrasher that need increased protection.

U.S. National Wildlife Refuges like the Lower Rio Grande Valley NWR in south Texas provide essential habitat for Curve-billed Thrashers, and a great number of other species throughout the U.S. and its territories. Unfortunately, the refuge system is often under-funded during the U.S. government’s budgeting process. To learn more about how you can help gain much needed funding for U.S. National Wildlife Refuges, visit: http://www.audubon.org/campaign/refuge_report/

Information on where Curve-billed Thrashers occur and in what numbers is vital to conserving the species. Help in monitoring this and other species by reporting your sightings to eBird. A project of Audubon and the Cornell Lab of Ornithology, eBird is the world’s first comprehensive online bird monitoring program: http://www.audubon.org/bird/ebird/index.html

Volunteers are crucial to the success of programs that monitor the status of populations of Curve-billed Thrashers and other bird species. Audubon’s Christmas Bird Count (CBC) is one of the longest-running citizen-science monitoring programs in the world and has helped to follow changes in the numbers and distribution of Curve-billed Thrashers. To learn more about the CBC and how you can participate, visit: http://www.audubon.org/bird/cbc

CIPAMEX, Audubon’s BirdLife International partner in Mexico, has an Important Bird Areas program that is working to protect habitat for Curve-billed Thrasher and many other species. To learn more about Mexico’s Important Bird Areas program and how you can help visit: http://132.248.79.80/wwwcampus/cipamex/

References
Brewer, D. 2001. Wrens, Dippers, and Thrashers. Yale University Press, New Haven, CT.

Kaufman, K. 1996. Lives of North Americna Birds. Houghton Mifflin Company, Boston, MA.

Tweit, Robert C. 1996 Curved-billed Thrasher (Toxostoma curviostre). In the Birds of North America, No. 235 (A Poole and F. Gills eds.). The Academy of National Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.