Two North American Song Populations of the Marsh Wren Reach Distributional Limits in the Central Great Plains

The Marsh Wren (Cistothorus palustris), like several other North American avian taxa, consists of eastern and western counterparts with distributional limits in the Great Plains. One style of Marsh Wren singer occurs to the east of a northwest-southeast, 100-km-wide "no-wren" corridor centered on O'Neill, Nebraska. These eastern males have relatively simple songs that usually begin with a characteristic nasal buzz followed by a song that consists largely of a series of brief tonal notes. The diversity of sounds is low, both in the number of different songs in a repertoire and in the contrast between different songs within that repertoire. Males to the west of the corridor have much larger repertoires of song types that contain both tonal sounds and harsh, broad-band sounds; the overall variety of sounds is exceptionally high. Some behavioral differences, such as song repertoire size, are genetically based, but others, such as the song structure and tonal quality, are culturally based. Two males singing the eastern style, with no evidence of hybrid singing behaviors, were found among the easternmost western populations, suggesting that little if any interbreeding occurs in the central Great Plains of the United States.