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The control of singing in varied thrushes Whitney, Carl Linn

Abstract

Male varied thrushes (Zoothera naevius) have repertoires of three to seven different songs. A typical song is a pure tone, about two seconds long and modulated in amplitude; it can be described quantitatively by its dominant frequency (Hz) and period of modulation. Reduced to these two dimensions, the songs within repertoires are more dissimilar to each other than would be expected if they were drawn at random from all the songs in the population. This pattern is consistent with a theory that explains the adaptive significance of song and song repertoires. According to the theory, song helps territorial males to repel other males and to attract and stimulate females, and repertoires enhance these effects by reducing the rate at which other birds habituate. This being so, it is to the advantage of males to have repertoires of dissimilar songs, since other birds will generalize less between the songs and will therefore habituate at a slower rate. The relationship between generalization and similarity of songs forms the basis of a theory of how singing is controlled by the brain of a varied thrush. The theory assumes that a control center feeds motivational impulses to units in charge of the different songs. When the motivational state of a unit reaches a threshold, the unit produces a song and then inhibits itself, dropping abruptly to a lower motivational state. At the same time, it inhibits each of the other units an amount that is directly proportional to the similarity of the songs produced by the two units. Some random variability in inhibition is not explained by this relationship. k simulation model based on this theory accounts for the following patterns found in sequences of songs produced by varied thrushes: 1) Once a song has been sung, it is not usually repeated immediately. 2) Songs are not sung with equal frequency. 3) The most common song in a repertoire is more likely than any other to be repeated immediately. 4) There is a negative correlation between the lengths of successive recurrence intervals (where a recurrence interval is defined as one plus the number of other songs between successive repetitions of a given song). 5) The two most dissimilar songs in a repertoire are more likely to be sung in succession than would be expected if they occurred independently of each other. 6) When several of the songs in a repertoire are dropped and replaced by others, the ones that remain occur in different relative frequencies. 7) Two very similar songs in a repertoire can occur with quite different frequencies. 8) Intervals between successive songs are variable but are usually at least several seconds long. 9) The average lengths of the intervals following different songs are positively correlated with the relative frequencies of the songs. 10) The absolute variability of the intervals between successive songs is positively correlated with the rate of singing. The theory can be elaborated to account for patterns of singing in other species.

Item Metadata

Title
The control of singing in varied thrushes
Creator
Whitney, Carl Linn
Publisher
University of British Columbia
Date Issued
1979
Description
Male varied thrushes (Zoothera naevius) have repertoires of three to seven different songs. A typical song is a pure tone, about two seconds long and modulated in amplitude; it can be described quantitatively by its dominant frequency (Hz) and period of modulation. Reduced to these two dimensions, the songs within repertoires are more dissimilar to each other than would be expected if they were drawn at random from all the songs in the population. This pattern is consistent with a theory that explains the adaptive significance of song and song repertoires. According to the theory, song helps territorial males to repel other males and to attract and stimulate females, and repertoires enhance these effects by reducing the rate at which other birds habituate. This being so, it is to the advantage of males to have repertoires of dissimilar songs, since other birds will generalize less between the songs and will therefore habituate at a slower rate. The relationship between generalization and similarity of songs forms the basis of a theory of how singing is controlled by the brain of a varied thrush. The theory assumes that a control center feeds motivational impulses to units in charge of the different songs. When the motivational state of a unit reaches a threshold, the unit produces a song and then inhibits itself, dropping abruptly to a lower motivational state. At the same time, it inhibits each of the other units an amount that is directly proportional to the similarity of the songs produced by the two units. Some random variability in inhibition is not explained by this relationship. k simulation model based on this theory accounts for the following patterns found in sequences of songs produced by varied thrushes: 1) Once a song has been sung, it is not usually repeated immediately. 2) Songs are not sung with equal frequency. 3) The most common song in a repertoire is more likely than any other to be repeated immediately. 4) There is a negative correlation between the lengths of successive recurrence intervals (where a recurrence interval is defined as one plus the number of other songs between successive repetitions of a given song). 5) The two most dissimilar songs in a repertoire are more likely to be sung in succession than would be expected if they occurred independently of each other. 6) When several of the songs in a repertoire are dropped and replaced by others, the ones that remain occur in different relative frequencies. 7) Two very similar songs in a repertoire can occur with quite different frequencies. 8) Intervals between successive songs are variable but are usually at least several seconds long. 9) The average lengths of the intervals following different songs are positively correlated with the relative frequencies of the songs. 10) The absolute variability of the intervals between successive songs is positively correlated with the rate of singing. The theory can be elaborated to account for patterns of singing in other species.
Genre
Thesis/Dissertation
Type
Text
Language
eng
Date Available
2010-03-18
Provider
Vancouver : University of British Columbia Library
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
DOI
10.14288/1.0094779
URI
http://hdl.handle.net/2429/22063
Degree
Doctor of Philosophy - PhD
Program
Zoology
Affiliation
Science, Faculty of; Zoology, Department of
Degree Grantor
University of British Columbia
Campus
UBCV
Scholarly Level
Graduate
Aggregated Source Repository
DSpace

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For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.