Macrogeographic variation in the song of the Mourning Warbler (Oporornis philadelphia)

Studies of macrogeographic variation in birdsong involve populations incapable of interbreeding because of physical barriers or separation by large distances. Different patterns have emerged from these studies such as (i) little or no variation exists among individuals or populations from the breeding range, (ii) individual variation is greater than among population variation resulting in no geographic structure, (iii) clinal variation, and (iv) macrogeographic variation where all individuals from several populations on the breeding range share a common song type forming a regional dialect or regiolect. I studied macrogeographic variation in song of the Mourning Warbler (Oporornis philadelphia (A. Wilson, 1810)). The observed pattern was similar to the fourth category of geographic variation with regiolects. A Western regiolect extended from northern Alberta to western Ontario. An Eastern regiolect stretched eastward from western Ontario and Wisconsin to the Gaspe Peninsula and New England, then southward through the Appalachians to West Virginia. Nova Scotia and Newfoundland each had unique regiolects. Finally, I compared these results to other species with regiolects and assessed the ability of some deterministic hypotheses to explain song divergence (e.g., role of morphology, physical barriers, island isolation).