Rm. Seyfarth et al., THE ACOUSTIC FEATURES OF GORILLA DOUBLE GRUNTS AND THEIR RELATION TO BEHAVIOR, American journal of primatology, 33(1), 1994, pp. 31-50
Mountain gorillas (Gorilla gorilla beringei) give double-grunts to one
another in a variety of situations, when feeding, resting, moving, or
engaged in other kinds of social behavior. Some double-grunts elicit
double-grunts in reply whereas others do not. Double-grunts are indivi
dually distinctive, and high-ranking animals give double-grunts at hig
her rates than others. There was no evidence, however, that the probab
ility of eliciting a reply depended upon either the animals' behavior
at the time a call was given or the social relationship between caller
and respondent. The probability of eliciting a reply could be predict
ed from a double-grunt's acoustic features. Gorillas apparently produc
e at least two acoustically different subtypes of double-grunts, each
of which conveys different information. Double-grunts with a low secon
d formant (typically < 1600 Hz) are given by animals after a period of
silence and frequently elicit vocal replies. Double-grunts with a hig
h second formant (typically > 1600 Hz) are given by animals within 5 s
of a call from another individual and rarely elicit replies. (C) 1994
Wiley-Liss, Inc.