Species limits and recent population history in the Curve-billed Thrasher

We surveyed 1,115 base pairs of mitochondrial DNA sequence from three gene regions in 66 Curve-billed Thrashers (Toxostoma curvirostre) taken from thr oughout their range. We found that populations sorted unambiguously into th ree groups. Two of these groups, the Curvirostre and Palmeri groups, have b een known for many years because of their distinctive phenotypic characteri stics, and their status was recently confirmed with an intensive morphometr ic analysis. The third (southern) group consists of populations in Puebla a nd Oaxaca, Mexico. The strong morphological and mtDNA distinctiveness of th e Curvirostre and Palmeri groups suggests that they warrant species status. We recommend that more specimens of the southern group be obtained prior t o formal taxonomic recognition of this form. Coalescence analyses suggest t hat the Curvirostre group has undergone a recent population increase, where as the Palmeri group seems to have been more stable in its Sonoran Desert r ange.