White-handed Gibbon × Pileated Gibbon

Hylobates lar × Hylobates pileatus

Mammalian Hybrids



Hylobates lar
White-handed gibbon (H. lar) Image: Wikimedia, BirdPhotos.com

Hylobates pileatus
Pileated gibbon (H. pileatus) Image: Su Neko, Wikimedia

Extensive hybridization between these two gibbons occurs on the headwaters of Takhong River, about 120 km northeast of Bangkok, Thailand in Khao Yai National Park. This reversible cross was also formerly very common in zoos (modern zoos now typically avoid keeping animals in the same cage if they are considered likely to hybridize). The hybrids are light in color at birth, but darken with age. Female hybrids have produced offspring.

Among 61 gibbon groups in the contact zone, at least 18 contained hybrids Backcross hybrids are not, however. easily recognizable. Brockelman and Gittins say an index of morphological traits shifted from 90% lar to 90% pileatus over a distance of nine kilometers. Brockelman (1978, p. 317) suggests that human activities have reduced contact between lar and pileatus (and thus hybridization) through disruption of much of a preexisting contact zone:

South of Khao Yai Park lie rice fields which extend to the Gulf (of Thailand), and we will never know what separated the species in this region; perhaps it was the Bang Pakong River which drains into the northeastern corner of the Gulf. Possibly there was a broad zone of interspecific contact in the upper reaches of the river (see also Brockelman and Gittins, 1984, p. 504).

Giessmann (1991, p. 361) suggests that this original contact zone was probably about 120 km long. In another paper, the same author analyzed the songs of these hybrids. There he states (Geissmann 1984, p. 232) that the features characterizing their song

generally also occur in other hylobatids (not necessarily the parental species). It is almost exclusively the combination of these features which seems to be new in the hybrid song. The song characteristics of both hybrids show influences from H. pileatus as well as from H. lar, and some characteristics are intermediate to those of each parental species.

In certain characteristics, the song of male hybrids resembles that of H. agilis. But it also contains three-part motifs not present in either parent’s song, and that, thus, cannot be explained by simple combination of their song characteristics. In addition, Giessmann says the “great-call” of female hybrids is remarkably similar to H. moloch’s.

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By the same author: Handbook of Avian Hybrids of the World, Oxford University Press (2006).

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