Hylobates muelleri

Short phrases consisting of simple hoots and more complex hoots, short trills, and occasional short quavering notes in males. Quavering notes are much less pronounced and shorter than in H. lar. Particularly prominent in this species are short phrases beginning with two or three wa-notes, each slightly lower in frequency than the preceding one. Short phrases of females almost exclusively with simple hoots. Some males were heard to produce relatively soft, squealing sounds between their short phrases, similar to males of H. agilis. Female great call with an acceleration-type climax, like H. moloch, but with much faster, bubbling note production (the single notes of the trill are not perceived as such by human ear), and without becoming slower at the end of the great call. Male optionally produces coda, sometimes accompanied by female. Male solo song bouts.

a. male short phrases (Doué-la-Fontaine Zoo, France, 25 May 1988; and Banham Zoo, 14 Oct. 1988)
b. great call sequnce consisting of female great call with male contribution (here accompanied by female short phrase) (Paignton Zoo, United Kingdom, 22 Oct. 1988)