- Toxostoma curvirostre
Identification
This species shows mostly light brown to buffy colors. Eyes are yellow to orange, bill is dark and slightly downcurved, less curved and shorter in juvenile. Throat is often whitish with a dusky malar stripe, lores are sligthly dusky, there is a hint of a light supercilium, and the entire underside is lighter than the upperside.
Differentiation between the Eastern curvirostre group and the Western palmeri group (see section on Taxonomy) relies mainly on more contrastingly patterned breast and abdomen, more visible wing bars, and on stronger white spots at the tips of the tail feathers in the curvirostre group.
Distribution
Curve-billed Thrasher is found in Mexico from just north of the Isthmus to Texas, New Mexico, and Arizona, as well as the driest corners of Oklahoma, Kansas, and Colorado. The separation of the two main groups is supposed to be caused by the Sierra Madre Occidental in Mexico and continue into Arizona, where there is an overlap in the south-east corner.
Taxonomy
This species has traditionally been divided into seven subspecies. A paper by Rojas-Soto (2003; see external links below) argues that this treatment is wrong, and that instead there is a main division into an Eastern group called the curvirostre group and a Western group called the palmeri group. In addition, populations on Tiburon and San Esteban Islands in the Gulf of California should be recognized as either full species or a subspecies. This split of Curve-billed Thrasher has not (at least yet) been recognized by the major world-wide taxonomic authorities, but the recognition of two groups that differ from each other in morphology was also made in Howell and Webb's guide to the birds of Mexico and northern Central America. If the split were to be accepted, one group would become Western Curve-billed Thrasher Toxostoma palmeri and the rest would retain the scientific name Toxostoma curvirostre.
