Behaviour 2019
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Males, but not females, respond to vocal senescence in swamp sparrow song
Stephen Nowicki1, Matthew N. Zipple1, William A. Searcy2, Susan Peters1. 1Duke University, Durham, NC, United States; 2University of Miami, Miami, FL, United States

Age-related changes in assessment signals occur in many animals, including humans. A longitudinal study of age-related changes in swamp sparrow (Melospiza georgiana) song revealed that males exhibit delayed maturation of song, as has been described for several species, followed by behavioral senescence, a less well-studied phenomenon. We used territorial playbacks to ask if male receivers perceive and respond differently to song changes associated with this behavioral senescence, comparing responses to songs recorded from 2-year-old males to responses to songs recorded from those same males when they were 10 years old. Territorial males gave stronger aggressive responses to songs of 2-year-old males as compared to songs of 10-year olds, consistent with the interpretation that senescent males are deemed less threatening rivals. We then used copulation solicitation assays to ask the same question of females. Contrary to our prediction, females did not discriminate between peak-aged and senescent males, responding equally to both. We suggest that this difference between male and female response may be the result of the two sexes attending to different song characteristics