Thursday, June 5, 2014

Curve-billed (Plateau) Thrasher

Next up at the Edinburg, Texas, bird feeder on 21 February 2014, was a Curve-billed Thrasher. This species probes in the ground litter for insects and seeds. It also consumes berries and cactus fruit. Curve-billed Thrashers are tolerant of a range of habitats and seems to coexist with people. Just how this thrasher will survive the extreme development of the Texas brush country, however, remains to be seen (Tweit 1996).

Curved-billed Thrashers in the Arizona Sonoran Desert and northwestern Mexico may be a different species from those in the Chihuahuan Desert, Texas, and central Mexico. The two populations do not overlap and their mitochondrial DNA differs. Among other field marks, eastern birds have light breasts, which make their spotting more distinct. Western birds have grayer breasts, with resultant less distinct spots. Western birds also have less distinct wing-bars. Compare this Texas bird with one I took in 2012 in southern Arizona. For the time being, the two populations are considered to be subspecies. But the question of splitting Curve-billed Thrasher into an eastern Plateau Thrasher and a western Palmer's Thrasher is currently on the agenda of the American Ornithologists' Union's checklist committee.

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