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Hoolock hoolock and H. leuconedys

Short phrases of bi-phasic hoots ("ow-wa"), simple hoots, high pitched eeks, and low pitched growls. Bi-phasic hoots consist of notes alternatingly produced during exhalation and inhalation, as in Hylobates agilis (contra Haimoff, 1984). Short phrases are produced by either sex. Apparently no sex-specific notes in song repertoire of this species. Female great call with an acceleration-type climax, like H. moloch, of moderate speed, usually becoming slower near end. Great call notes mainly bi-phasic. Male usually begins vocalising halfway through the great call. Mated pairs typically produce duet song bouts only.

No vocal differences are known to occur between the western hoolock (Hoolock hoolock) and the eastern hoolock (H. leuconedys).

a. male short phrases (Kunming Inst. Zool., China, Oct. 1988, rec: Lan Daoying)
b. great call sequnce consisting of female great call with overlapping male contributions (Kunming Zoo, China, 27 July 1990)

Hoolock hoolock and H. leuconedys sound examples:
Press to start sound Group song, Kunming Zoo, China, 27 Juli 1990.
Although most of the singing is provided by the subadult male "Jian-Jian" and the adult female "Gui-Gui" (singing in adjacent cages), several other immature hoolocks also contributed to the song bout.
Press to start sound Group song, Kunming Zoo, China, 27 Juli 1990.
Same recording as above, later in the song bout.
Press to start sound Solo song, solitary adult male, Kunming Institute of Zoology, China, Oct. 1988 (rec. Lan Daoying).
Press to start sound Alarm calls, family group, forest fragment 3.5 km north of Lawachara National Park, Sylhet division, NE Bangladesh, 19 May 2009 (rec. Alice Brindle). The adult pair and juvenile offspring (4-5 year old) are calling. A chicken is calling in the foreground.