The Minds and Manners of Wild Animals: A Book of Personal Observations

The gibbons (including the siamang) have tremendous voices, with numerous variations, and they love to use them. My acquaintance with them began in Borneo, in the dense and dark coastal forest that there forms their home. I remember their cries as vividly as if I had heard them again this morning. While feeding, or quietly enjoying the morning sun, the gray gibbon (Hylobates concolor) emits in leisurely succession a low staccato, whistle-like cry, like "Hoot! Hoot! Hoot!" which one can easily counterfeit by whistling. This is varied by another whistle cry of three notes, thus: "Who-ee-hoo! Who-ee-hoo!" also to be duplicated by whistling. In hunting for specimens of that gibbon, for American museums, I could rarely locate a troop save by the tree- top talk of its members. But all this was only childish prattle in comparison with the daily performances of the big white-handed, and the black hoolock gibbons, now and for several years past residing in our Primate House. Every morning, and perhaps a dozen times during the day, those three gibbons go on a vocal rampage and utter prolonged and ear-splitting cries and shrieks that make the welkin ring. The shrieking chorus is usually prolonged until it becomes tiresome to the monkeys. In all our ape and monkey experience we never have known its equal save in the vocal performances of Boma, our big adult male chimpanzee, the husband of Suzette. 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.