A baboon emits occasionally, and without any warning, a fearful explosive bark, or roar, that to visitors is as startling as the report of a gun. The commonest expressions are "Wah!" and "Wah'-hoo!", and the visitor who can hear it close at hand without jumping has good nerves.
The big and solemn long-nosed monkey of Borneo (Nasalis larvatus) utters in his native tree-top (overhanging water), a cry like the resonant "honk" of a saxophone. He says plainly, "Kee honk," and all that I could make of its meaning was that it is used as the equivalent of "All's well."
Of all the monkeys that I have ever known, either wild or in captivity, the red howlers of the Orinoco, in Venezuela, have the most remarkable voices, and make the most remarkable use of them. The hyoid cartilage is expanded,—for Nature's own particular reasons,—into a wonderful sound-box, as big as an English walnut, which gives to the adult voice a depth of pitch and a booming resonance that is impossible to describe. The note produced is a prolonged bass roar, in alternately rising and falling cadence, and in reality comprising about three notes. It is the habit of troops of red howlers to indulge in nocturnal concerts, wherein four, five or six old males will pipe up and begin to howl in unison. The great volume of uncanny sound thus produced goes rolling through the still forest, far and wide; and to the white explorer who lies in his grass hammock in pitchy darkness, fighting off the mosquitoes and loneliness, and wondering from whence tomorrow's meals will come, the moral effect is gruesome and depressing.
In captivity the youthful howler habitually growls and grumbles in a way that is highly amusing, and the absurd pitch of the deep bass voice issuing from so small an animal is cause for wonder.
It is natural that we should look closely to the apes and monkeys for language, both by voice and sign. In 1891 there was a flood of talk on "the speech of monkeys," and it was not until about 1904 that the torrent stopped. At first the knowledge that monkeys can and do communicate to a limited extent by vocal sounds was hailed as a "discovery"; but unfortunately for science, nothing has been proved beyond the long-known fact that primates of a given species understand the meaning of the few sounds and cries to which their kind give utterance.
Thus far I have never succeeded in teaching a chimpanzee or orangutan to say even as much as "Oh" or "Ah." Nothing seems to be further from the mind of an orang than the idea of a new vocal utterance as a means to an end.
Our Polly was the most affectionate and demonstrative chimpanzee that I have ever seen, and her reaction to my voice was the best that I have found in our many apes. She knew me well, and when I greeted her in her own language, usually she answered me promptly and vociferously. Often when she had been busy with her physical- culture exercises and Delsartean movements on the horizontal bars or the trapeze in the centre of her big cage, I tested her by quietly joining the crowd of visitors in the centre of the room before her cage, and saying to her: "Polly! Wah! Wah! Wah!"
Nearly every time she would stop short, give instant attention and joyously respond "Wah! Wah! Wah!", repeating the cry a dozen times while she clambered down to the lower front bars to reach me with her hands. When particularly excited she would cry "Who-oo! Who-oo! Who-oo!" with great clearness and vehemence, the two syllables pitched four notes apart. This cry was uttered as a joyous greeting, and also at feeding-time, in expectation of food; but, simple as the task seems to be, I really do not know how to translate its meaning into English. In one case it appears to mean "How do you do?" and in the other it seems to stand for "Hurry up!"
Polly screamed when angry or grieved, just like a naughty child; and her face assumed the extreme of screaming-child expression. She whined plaintively when coaxing, or when only slightly grieved. With these four manifestations her vocal powers seemed to stop short. Many times I opened her mouth widely with my fingers, and tried to surprise her into saying "Ah," but with no result. It seems almost impossible to stamp the vocal-sound idea upon the mind of an orang-utan or chimpanzee. Polly uttered two distinct and clearly cut syllables, and it really seemed as if her vocal organs could have done more if called upon.
The cries of the monkeys, baboons and lemurs are practically nothing more than squeals, shrieks or roars. The baboons (several species, at least) bark or roar most explosively, using the syllable "Wah!" It is only by the most liberal interpretation of terms that such cries can be called language. The majority express only two emotions—dissatisfaction and expectation. Every primate calls for help in the same way that human beings do, by shrill screaming; but none of them ever cry "Oh" or "Ah."