The western subspecies of Yellow-billed Cuckoo Coccyzus americanus occidentalis has undergone severe population declines over the last two decades. Numerous petitions have warranted its listing under the Endangered Species Act; however, the question of whether the western subspecies is genetically separated from the eastern C. a. americanus form is controversial. Previous research found small, but significant divergence in a single mitochondrial gene based on a limited number of samples. In this study, I analyze 949 base pairs of the same mitochondrial cytochrome b gene from additional samples in both the western and eastern subspecies to reassess the evolutionary distinctiveness of the western taxa. Unlike the previous study, I did not find any fixed genetic differences, but only found slight, insignificant genetic differentiation between the subspecies. The separation into distinct subspecies of the eastern and western Yellow-billed Cuckoo might be more recent than can be captured by a single mitochondrial gene; alternatively high levels of gene flow might prevent complete segregation. Interestingly, I found a substantial amount of haplotype variation within the western samples, which may indicate genetic differences between western sampling locations. Future studies incorporating next generation sequencing are recommended to resolve the taxonomic status of Yellow-billed Cuckoo.
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Vol. 101 • No. 2