PHENOTYPIC VARIATION IS CLINAL IN THE YELLOW-THROATED WARBLER

Subspecies are assumed to have unique evolutionary histories, but molecular data sometimes contradict subspecies designations based on morphology. A recent genetic survey of the Yellow-throated Warbler (Dendroica dominica) found that none of its three continental subspecies qualified as evolutionarily significant units. I performed a range-wide morphological assessment of the continental Yellow-throated Warbler subspecies in an effort to quantify their differences and examine if and how subspecific differences related to geography. Results indicated much overlap in the morphological characters most important in diagnosing Yellow-throated Warbler subspecies (bill length and the proportion of yellow in the lores), and discriminant function analysis failed to correctly assign most individuals, especially those collected near a subspecies border. There was a strong west-to-east clinal change in bill length and the proportion of yellow in the lores and no evidence of discrete morphological groups. I recommend eliminating the subspecies D. d. albilora and D. d. stoddardi because they cannot be reliably diagnosed by morphology or mtDNA.