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Hylobates agilis (and H. albibarbis) |
Short phrases consisting of simple hoots, more complex hoots ("whoo-aa") and bi-phasic hoots are uttered by males and females. Bi-phasic hoots consist of notes alternatingly produced during exhalation and inhalation ("whoo-aa"). Some males were heard to produce relatively soft, squealing sounds between their short phrases, similar to males of H. muelleri. Female great call consisting of long notes of modulated frequency. A first, often very weak climax in frequency is reached at the beginning of the great-call; a second, more pronounced climax of higher frequency notes occurs near the end of the great call. Male produces coda. Male solo song bouts and duet song bouts.
No clear vocal differences are known to occur between the agile gibbon (Hylobates agilis) and the white-bearded gibbon (H. albibarbis).
a. Male short phrases (Twycross Zoo, United Kingdom, 2 Oct. 1988; and Guangzhou Zoo, China, 7 Sept. 1990)
b. Great-call sequnce consisting of female great-call with male contribution (Asson Zoo, France, 31 May 1988)