Sounds of senescence: Male swamp sparrows respond less aggressively to the songs of older individuals

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2021-01-01

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Naguib, Marc

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Abstract

Age-related changes in assessment signals occur in a diverse array of animals, including humans. Age-related decline in vocal quality in humans is known to affect perceived attractiveness by potential mates and voters, but whether such changes have functional implications for nonhuman animals is poorly understood. Most studies of age-related change in animal signals focus on increases in signal quality that occur soon after the age of first breeding (“delayed maturation”), but a few have shown that signal quality declines in older individuals after a mid-life peak (“behavioral senescence”). Whether other individuals are able to detect this senescent decline of assessment signals has not previously been tested. Here we use playback experiments to show that wild male swamp sparrows (Melospiza georgiana) respond more aggressively to songs from 2-year-old males as compared with songs from the same males when they are 10 years old. Senescence in signals that, like birdsong, affect reproductive success through intrasexual competition or mate choice may be of evolutionary significance. Lay Summary: Using playback experiments with wild swamp sparrows (Melospiza georgiana), we demonstrate that listeners both detect and respond to age-related declines in vocal quality. Two previous studies have shown that some song characteristics deteriorate with age later in life in songbirds, but to our knowledge this is the first demonstration outside of humans that such deterioration affects receiver response. Discrimination of songs from males of different ages may have evolutionary implications.

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10.1093/BEHECO/ARZ218

Publication Info

Zipple, MN, S Peters, WA Searcy and S Nowicki (2021). Sounds of senescence: Male swamp sparrows respond less aggressively to the songs of older individuals. Behavioral Ecology, 31(2). pp. 533–539. 10.1093/BEHECO/ARZ218 Retrieved from https://hdl.handle.net/10161/26536.

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Scholars@Duke

Nowicki

Stephen Nowicki

Professor of Biology

Our lab studies animal communication, asking both proximate and ultimate questions about how signaling systems function and how they evolve. Most of our work is done with birds, although lab members have studied a variety of other taxa. One major theme that runs through our work is to understand how signal reliability (“honesty”) is maintained in the face of the competing evolutionary interests of signal senders and receivers. We use both laboratory experiments and field-based analyses to test hypotheses about the costs of signal production, which theory suggests are necessary to maintain reliability. For example, we have demonstrated that the reliability of birdsong as a signal of quality in the context of mate choice is maintained by variation in the response of young birds to early developmental stress, which in turn affects brain development and song learning. Another theme that runs through our work concerns how animals themselves perceive signals, in particular the role of categorical perception in communication. Our work here began with birdsong, for example demonstrating context-dependent variation in category boundaries that define the smallest acoustic units of song (“notes”), and identifying categorical responses of neurons in the “song system” of the brain to variation in those notes. More recently, we have begun to study categorical perception in visual signaling, demonstrating for example that the carotenoid-based orange-red coloration commonly used in assessment signaling may be perceived categorically. This finding illustrates the connection between our interests in perception and reliability, given that canonical models of reliability assume continuous perception.


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