Date of Award:

5-1-1980

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

Keith L. Dixon

Committee

Keith L. Dixon

Committee

E. C. Oaks

Committee

B. Gilbert

Committee

I. Palmblad

Committee

J. Gessaman

Abstract

Although song in passerines typically is limited to males, there are many reports of singing by females. This study was undertaken to ascertain the incidence and possible functions of such singing in the Black-headed Grosbeak, Pheucticus melanocephalus. The singing of grosbeaks is expressed in a series of syllables lying between about 1.5 and 4.0 kHz. The number of syllables in the repertoires of the birds studied ranged from 14 to 37 in males and 4 to 28 in females. Within the most extensively studied population, an average of one-third of any male's syllables also were sung by another male. However, males from other populations shared very few syllables with the above males. About one-tenth of any female grosbeak's syllables were sung by other females in the population. In addition, males and females shared very few syllables. The songs of male and female grosbeaks also differed in the average number of syllables per song, average duration of songs, average intersyllable duration, and predictability of syllable sequences. Male and female grosbeaks also differed in the seasonal timing of their singing. Singing by males peaked during the period of territory acquisition; whereas, females generally did not begin singing until just prior to the fledging of their young. Responses by territorial males to the playback of the songs of non-neighboring males were significantly stronger than those to neighbors' songs when played at the territorial boundary, as well as in the center of the territory. In contrast, females showed no significant responses to the songs of either neighboring or non-neighboring males. Further, neither males nor females showed any significant responses to the songs of non-neighboring females. And, whereas females responded significantly to the songs of their mates, the responses of territorial males to their mates were not significant. The results of the present study suggest that whereas the singing of male grosbeaks is utilized in the acquisition and maintenance of territory, singing by females has no significance in territorial behavior. Further, playback experiments indicate that singing by females plays no role in the maintenance of the pair bond. It is suggested, however, that the singing of female grosbeaks is utilized in maintaining the cohesiveness of family groups after the young fledge. Among older fledglings contact with parents usually results from these birds flying to the parents in response to parental song. However, younger fledglings, as well as birds which have left the nest prematurely, maintain contact in the following manner: an adult with food, but unaware of the location of its young, will begin singing. Such singing elicits begging from the young and enables a parent to locate its young. The responses of females to the playback of the begging calls of their young appear to verify the existence of such a system. Upon hearing the playback, females showed a significant approach response as well as significant increases in the number of flights and "chip" calls. Such responses would enable a parent to quickly locate a young grosbeak. On the other hand, once playback ended females showed significant increases in singing rates. Under natural conditions this would elicit calling by young grosbeaks and allow a parent to locate its offspring.

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