Date of Award:

1988

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Advisor/Chair:

Keith L. Dixon

Abstract

I recorded the songs and studied the reproductive behavior of a population of marked House Wrens (Troglodytes aedon) to identify patterns of singing and correlate them with behavioral contexts and stages of the breeding cycle. I found that House Wren singing could be organized into three hierarchical regimes: routine patterns of daily singing, context-specific patterns of singing and long-term fluctuations in singing rate throughout the breeding cycle. During routine daily singing, predictable structural changes occurred. Songs were clustered in discrete groups called bouts. The songs within a bout were more similar in structure than songs from different bouts. Although I found no distinctive combination of notes associated with any particular context, three context-specific patterns of singing were identified. These included male:male, courtship and within-pair singing. Songs delivered in these contexts differed from songs sung in the absence of close listeners by virtue of increased length and complexity of the introductory portion of the song. Through playback experimentation, I found that introductory notes evoke a stronger response from listeners than other notes. These notes have rapid attenuation characteristics and transmit well only for short distances. Use of songs that emphasize these notes would be consistent with providing the appropriate "privacy" of communication between individuals in contexts where "public" broadcast may unnecessarily attract rivals.

Long-term fluctuations in singing rate correlated with the various stages of the breeding cycle in a predictable fashion. The highest rate of singing occurred during the establishment of a territory, following which singing rate declined through the end of the egg-laying period. During the late egg-laying period, many birds entered a brief silent period. In the incubation period, singing levels rose to moderate levels, then dropped off again after the young hatched. Over the course of the nesting cycle, the proportion of short songs increased.

I propose the "Neighborhood Watch Hypothesis" as a possible explanation of the evolutionary advantage of large, variable repertoires. This hypothesis asserts that the large repertoire and long-term pattern of singing by established residents facilitate their recognition and expulsion of intruders who pose a threat to eggs and young.

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