Date of Award:

5-1975

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Emily C. Oaks

Committee

Emily C. Oaks

Committee

Keith L. Dixon

Committee

Allen W. Stokes

Abstract

Adult members of the species Microtus richardsoni were used to study the importance of acoustic communication in these voles. Tests were run with single individuals and nonbreeding pairs of voles to obtain recordings and sonagraphs of sounds emitted during exploration of a new cage, agonistic encounters, encounters with a potential predator and in response to miscellaneous aversive stimuli. Of the four groups of tests conducted, sounds were used by M. richardsoni during the last three. The results of this study showed that the water vole emitted ten different call types or sounds. These sounds were separated by similarity into Group I, Group II, tooth-chatter and miscellaneous sound types. Group I calls included the squeal, squawk, grind and complex. These calls were similar in intensity and in having harmonics extending into the ultrasonic range. The squeal consisted of a fundamental frequency plus several distinct, harmonically-related overtones. The squawk resembled the squeal, but the harmonics in the higher frequencies of the former call were obscured by noise. The complex was found to be a combination of two or all three of the other calls. The Group II call types emitted by the water vole were the voiced and voiceless whimpers. These two calls were similar in that each was emitted at low intensity and neither call had harmonics extending into the ultrasonic range. The voiceless whimper was different from the voiced whimper in that its harmonics were obscured by noise. The squawk, grind, complex, voiced whimper and voiceless whimper are inferred to be modifications of the squeal. The primary function of these six call types is postulated to indicate the degree of submissiveness of the vocalizing vole. Modification of the calls is probably related to the motivational state of the animal emitting the call. A secondary effect of the calls might be to inhibit further aggression by the opponent. A seventh sound emitted by the water vole was the tooth-chatter. This sound, also used by many other rodents, was used to communicate threat. The miscellaneous sounds emitted by these voles included the ultrasonic chirp, the peep and the "whooping" call. These calls were not emitted frequently enough to postulate their function. This study showed that sound is used mainly by Microtus richardsoni during agonistic situations and may be adaptive in inhibiting aggression. The use of the physical characteristics of sounds in determining taxonomic relationships is postulated.

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