Long-distance dependencies in birdsong syntax.
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2022-01
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Songbird syntax is generally thought to be simple, in particular lacking long-distance dependencies in which one element affects choice of another occurring considerably later in the sequence. Here, we test for long-distance dependencies in the sequences of songs produced by song sparrows (Melospiza melodia). Song sparrows sing with eventual variety, repeating each song type in a consecutive series termed a 'bout'. We show that in switching between song types, song sparrows follow a 'cycling rule', cycling through their repertoires in close to the minimum possible number of bouts. Song sparrows do not cycle in a set order but rather vary the order of song types from cycle to cycle. Cycling in a variable order strongly implies long-distance dependencies, in which choice of the next type depends on the song types sung over the past cycle, in the range of 9-10 bouts. Song sparrows also follow a 'bout length rule', whereby the number of repetitions of a song type in a bout is positively associated with the length of the interval until that type recurs. This rule requires even longer distance dependencies that cross one another; such dependencies are characteristic of more complex levels of syntax than previously attributed to non-human animals.
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Searcy, William A, Jill Soha, Susan Peters and Stephen Nowicki (2022). Long-distance dependencies in birdsong syntax. Proceedings. Biological sciences, 289(1967). p. 20212473. 10.1098/rspb.2021.2473 Retrieved from https://hdl.handle.net/10161/26533.
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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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