Geographic variation in call structure, likelihood, and call-song associations across subspecies boundaries, migratory patterns, and habitat types in the Marsh Wren (Cistothorus palustris)

ABSTRACT Geographic variation in acoustic signals can be important in species divergence, especially the maintenance of prezygotic barriers to gene flow. Furthermore, selective pressures on acoustic signals likely vary both across geographic distances and among vocalizations used in different behavioral contexts. We described the call repertoire of 5 subspecies of Marsh Wren (Cistothorus palustris) in eastern North America and tested for variation in both the acoustic structure and likelihood of production of each call type at 3 functional–ecological levels: subspecies identity, migratory pattern, and habitat type. Three of the 7 described call types exhibited acoustic variation best explained by either migratory pattern or habitat type. These calls were used principally in courtship–territorial patrol contexts, whereas 4 calls that did not exhibit geographic variation were used in agonistic interactions. How often a call is used in a population may be indicative of the behavior or breeding phenology asso...