Syntactic rules predict song type matching in a songbird
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2023-01-01
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Abstract: Song type matching has been hypothesized to be a graded signal of aggression; however, it is often the case that variation in matching behavior is unrelated to variation in aggressiveness. An alternative view is that whether an individual matches a song is determined mainly by syntactic rules governing how songs are sequenced. In song sparrows (Melospiza melodia), two such rules are the cycling rule, which directs that a bird cycles through its song types in close to the minimum number of bouts, and the bout length rule, which directs that a long bout of a song type is followed by a long interval before that song type is sung again. The effect of these rules on matching is confirmed here for a population of eastern song sparrows. Territorial males were challenged at the end of a recording session with playback of one of their own song types. Logistic regression showed that the probability of matching the playback song type increased with the length of the interval since the subject had last sung that song type, as predicted by the cycling rule. The probability of matching decreased as prior bout length increased, as predicted by the bout length rule. In a multivariate logistic regression, interval length and prior bout length were both associated with matching and together correctly predicted matching in 81.3% of cases. The results support the syntactic constraints hypothesis, which proposes that matching is a non-signaling by-product of internal rules governing the ordering of song type sequences. Significance statement: Vocal matching has attracted widespread interest in large part because it seems an effective method of directing an aggressive message at a particular recipient. Here, we show that in an eastern population of song sparrows, decisions on whether to match another bird are largely determined by internal rules of syntax governing how a singer sequences its song types, rather than by variation in aggressiveness or other individual traits. These results support the view that vocal matching is an incidental byproduct of internal mechanisms controlling the ordering of vocalization types and so is not a signal at all. This hypothesis may be broadly applicable to vocal matching in other species.
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Searcy, WA, LM Chronister and S Nowicki (2023). Syntactic rules predict song type matching in a songbird. Behavioral Ecology and Sociobiology, 77(1). 10.1007/s00265-022-03286-3 Retrieved from https://hdl.handle.net/10161/26527.
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Stephen Nowicki
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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