Gorilla

Species: Gorilla (gorilla gorilla beringei)

Use: Vocalizations

Authors: D. Fossey

Methods: N/A

Publications/Presentations: D. Fossey (1972). Vocalizations of the mountain gorilla (Gorilla gorilla beringei).Animal Behavior, 20, 36:53.

Behaviors: (See also: Fossey, D. (1983). Gorillas in the mist. Boston Houghton Mifflin.)

Roar: Monosyllabic loud outburst of low-pitched harsh sound, lasting from .20 to .65 seconds, beginning and ending abruptly. Individual differences in frequency concentrations. Heard only from silverbacks in situations of stress or threat, and primarily directed at human beings, although occasionally at buffalo herds. Always followed on the part of the emitter, with varying degrees of display, ranging from bluff charges to small forward lunges.

Alarm calls

Scream: Shrill and prolonged emission of extremely loud sound, lasting up to 2.13 seconds and repeated as often as 10 times. Individual differences not denoted. Screams heard from all age and sex classes, but most frequently from silverbacks. Vocalization heard most often during intragroup disputes, though could be directed toward human beings or ravens of alarm rather than threat was motivation for call.

Wraagh: Explosive monosyllabic loud vocal outburst not as deep as a roar nor as shrill as a scream. Began and ended abruptly and lasted between .2 and ,8 seconds. Individual differences in sound, were more harmonically structured than roars. Heard from all adults but most frequently from silverbacks. Usually precipitated by sudden situations of stress- the unexpected arrival of an observer, etc. Most effective in scattering group members and never accompanied by aggressive display behavior.

Question bark: Characteristic compositions of three notes with the first and third lower than middle, as if asking the question ÒWho are you?Ó Sound was short, lasting between .2 and .3 seconds heard more from silverbacks. Usually in situations of mild alarm or curiosity and was common response to discovery of obscured observer, etc.

Cries: Resembling wails of human infants, could build up into shrieks much like human beingsÕ temper tantrums. Emitted between .03 and .05 seconds apart, and could last for nearly 19 seconds. Wails had four distinct frequency concentrations, but shrieks were much less structured. Cries were heard only from infants or young juveniles, frequently when left alone. Cries built up into temper tantrums if stressful situation was prolonged.

Coordination Vocalization

Pig-grunts: Series of short, rough, guttural noises, pig-grunts are usually delivered between .15 and .4 seconds apart in sequences of nine or ten outbursts. Resembling grunting of pigs feeding tended to become louder and louder and more closely spaced if prolonged. Most frequently heard during traveling, when trail disputes and altercations over limited food resources were more apt to occur. Pig-grunts were effective rebuttal vocalizations and disciplinary enforcements between adults and young.

Belch-vocalizations: Deep, prolonged rumbles (naoom, naoom, naoom) rather like throat-clearing utterances. The belch vocalization is one of the most complex because of multiple intergradations and functional variations. Variations heard from all sex and age classes. For expressing contentment and verifying positions; a slightly shortened belch vocalization was often used when mildly disciplining gorilla young or observers.

Chuckles: Raspy expiration of noise verge in intensity depending on degree of play involved. Irregularly spaced spurts of sound varying from .02 to .1 seconds with low frequency concentration. No individual differences.

Intergroup variations

Hootseries preceding chestbeats: Given with or without a terminating chestbeat, consists of prolonged distinct hoo-hoo-hoos. Lowpitched, often undetectable to human ear at beginning, but usually built up into plaintive-sounding and longer hoots toward the end. The lengthier the series, the more fluctuations in harmony and phasing. Frequencies ranged between 1.4 and 1.8 kilocycles per second for as many as eighty-four hoots per second. Silverbacks were most frequent emitters. Depending on distance between groups, would o r would not terminate vocalizations with displays.