Note: Gould (1995, p. 466) says, "surveys of European and North American zoo gibbons in the early 1980s found that over 4% were definitely hybrids, and the real total would undoubtedly be considerably higher."
Hylobates agilis [Agile Gibbon]
See also: Hylobates albibarbus × H. muelleri.
× Hylobates hoolock (♂) [Western Hoolock Gibbon] CHR. DRS. Ashley Montagu (1950, p. 151) says the male parent (of unknown provenance) was "described as Hylobates lar pileatus", but the traits of the "animal appear to resemble more closely Hylobates hoolock than any other gibbon." However, Groves (1972, p. 42) insists that the cross in question was H. agilis × H. pileatus. The hybrid resembled a dark H. muelleri.
×Hylobates lar (♀) [White-handed Gibbon] CAENHR(northwestern peninsular Malaysia). Hybridization has been reported at the headwaters of the Muda River (see map in Geissmann 1995). However, Groves says human activities (logging and the creation of an artificial lake) have now "completely disrupted" the hybrid zone, so hybridization may be less common now than formerly. Brockelman and Gittins 1984; Gittins 1978, 1984; Groves 1993; Chiarelli 1961; International Zoo Yearbook 1966 (p. 391), 1972 (p. 320); Steiner 1949†.
× Hylobates muelleri [Müller’s Bornean Gibbon] CHR. DRS. International Zoo Yearbook 1984/1985 (p. 524), 1986 (p. 480), 1989 (p. 320), 1991 (p. 344). Picture
. × Hylobates pileatus (♂) [Pileated Gibbon] CHR. DRS. HPF(♀♀). Newman and Symmes 1982 (p. 269, citing Marshal and Brokelman) say a female hybrid reached the age of 35 and that her song combined elements of H. agilis and other hylobatids (not including H. pileatus). At least nine hybrids were produced at the Zurich Zoo. See: Hylobates agilis × H. hoolock. Groves 1972 (p. 43); International Zoo Yearbook 1962 (p. 225). Internet Citations: DEMO.
Hylobates albibarbus [White-bearded Bornean Gibbon]
× Hylobates muelleri (♂) [Müller’s Bornean Gibbon] ENHR(Indonesia, central Kalimantan). HPF(vh). The wide hybrid zone is in the vicinity of Muarajuloi (0˚12´S 114˚3´E), between the Busang and Murung rivers (headwaters of the Barito). Contact probably occurs as far west as the upper Kapuas River. The known portion of the zone covers several thousand square kilometers. Within it the gibbon population is relatively sparse (2.9 groups/sq. km.), a reflection perhaps of lower viability/fertility in hybrids. Within this zone, pure parental types are rare or non-existent. Hybrid calls are variably intermediate between those of the parents. These taxa were recently split. Albibarbus is sometimes treated as a Bornean race of H. agilis. Bodmer et al. 1991; Chivers and Burton 1991; Geissmann 1995 (pp. 150-151); Groves 1993; Maples and Haraway 1982; Marshall and Sugardjito 1986; Marshall et al. 1986; Mather 1992, 1999; McConkey and Chivers 2004; Short 2004.
Hylobates concolor [Black Crested Gibbon]
× Hylobates leucogenys (♀) [Northern White-cheeked Gibbon] CANHR. CON: northern Vietnam and adjacent China. Geissmann (1989, p, 462) says hybrids, especially male and immature animals, closely resemble H. leucogenys, and that for this natural hybrids "may not be reliably distinguishable from pure H. leucogenys on the basis of fur coloration,"Brandon-Jones et al. (2004, p. 152) say that H. leucogenys splits the range of H. concolor. Geissmann 1989, 1995a†; Groves 1972 (p. 61).
× Hylobates pileatus [Pileated Gibbon] CHR(Brookfield, Chicago)?? CON: Laos? A male hybrid was reported. Wolkin and Myers (1980, p. 205, citing Beck) say the report of this hybrid "was not confirmed." International Zoo Yearbook 1970 (p. 257).
Hylobates gabriellae [Buff-cheeked Gibbon]
× Hylobates leucogenys [Northern White-cheeked Gibbon] CANHR. DRS. These gibbons are sometimes lumped. The IUCN (Internet Citations: NOMSI) says the Southern White-cheeked Gibbon (Nomascus siki) "may not be a genuine species, but rather, a natural hybrid of N.[omascus] leucogenys and N. gabriellae." Nomascus leucogenys and Nomascus gabriellae are synonyms of Duff and Lawson’s (2004) Hylobates gabriellae and Hylobates leucogenys. International Zoo Yearbook 1983 (p. 317).
× Hylobates siki [Southern White-cheeked Gibbon] NHR. CON: southern Laos, southern Vietnam (~16˚N). Groves (1993, p. 111) says the frequency of hybridization is unknown. See: Hylobates gabriellae × H. leucogenys. Delacour 1951; Geissmann 1995b (p. 478); Groves 1972 (p. 60), 1993. Internet Citations: GIBB†, NOMSI.
Note: Two populations (hoolock, leuconedys), treated as races of Hylobates hoolock,
Hylobates hainanus [Hainan Gibbon]
× Hylobates leucogenys [Northern White-cheeked Gibbon] CHR. DRS. Twycross Zoo had a male hybrid in 1987. International Zoo Yearbook 1989 (p. 320).
Hylobates hoolock [Western Hoolock Gibbon]
See also: Hylobates agilis.
× Hylobates lar [White-handed Gibbon] CHR. CON: Myanmar (Salween River) International Zoo Yearbook 1974 (p. 373), 1977 (p. 307).
× Hylobates leuconedys [Eastern Hoolock Gibbon] NHR. CON: Myanmar. Groves (1972, p. 67) reported finding hybrids on the upper Chindwin River at Dalu (26˚26´N 96˚08´E). In this locale, according to the IUCN (Internet Citations: HOOLO), "there is a hybrid zone or cline between the two species (since they are almost certainly not reproductively isolated)." An introduced population of also occurs in Arunachal Pradesh, northeast India, within the Hylobates leuconedys range of H. hoolock (Das et al. 2006).
Note: Two populations (carpenteri, entelloides), treated as races of Hylobates lar, have a 70-km-wide hybrid zone in southeastern Thailand at the head of the Malay Peninsula. It extends northwest to southeast through the forests west of Bangkok from about from ~15˚18´N, 99˚33´E to ~14˚1´N, 100˚22´E. Groves 1993; Fooden 1969a, 1971; Groves 1970b, 1972 (Fig. 22 and pp. 75-76).
Hylobates lar [White-handed Gibbon]
See also: Hylobates agilis; H. hoolock.
× Hylobates moloch (♂) [Silvery Gibbon] CHR. DRS. HPF(♀♀). International Zoo Yearbook 1967 (p. 306), 1968 (p. 295), 1973 (p. 325), 1977 (p. 307), 1986 (p. 480), 1989 (p. 320).
× Hylobates muelleri (♀) [Müller’s Bornean Gibbon] ???COMPLETE ENTRY Marler and Tenaza (1977) say a male and a female hybrid, when adult, formed a mated pair. The song of the female combined elements of the both parents, while the male’s resembled that of H. lar. Geissmann 1984, 1993, 2000; Tenaza 1985.
× Hylobates pileatus (↔) [Pileated Gibbon] CAENHR(Thailand). HPF(♀♀). CON: Headwaters of Takhong River, about 120 km northeast of Bangkok (Khao Yai N.P.). See the separate article "White-handed Gibbon × Pileated Gibbon."
Hylobates leucogenys [Northern White-cheeked Gibbon] See: Hylobates concolor; H. gabriellae; H. hainanus.
Hylobates leuconedys [Eastern Hoolock Gibbon] See: Hylobates hoolock.
Hylobates moloch [Silvery Gibbon] See: Hylobates lar.
× Hylobates muelleri [Müller’s Bornean Gibbon] CHR. HPF. DRS. International Zoo Yearbook 1986 (p. 480), 1987 (p. 408), 1991 (p. 344).
Note: There are wide hybrid zones between the three populations (abbotti, funereus, muelleri) treated as races of H. muelleri (Marshall and Sugardjito 1986). Hill (1960) says that the zone between two of these populations (abbotti and funereus)is in Sarawak. He says (p. 30) that "specimens very close to abbotti can be found in the extreme south-west [of Sarawak] and typical funereus in the north-east but over most of the area Hylobates muelleri is represented by forms intermediate between these two races." Internet Citations: GIBB.
Hylobates muelleri [Müller’s Bornean Gibbon]
See also: Hylobates albibarbus; H. lar; H. moloch.
× Hylobates syndactylus (♀) [Siamang] CHR. DRS. These hybrids are known either as "gibbangs" or as "siabons." Two female hybrids were born to a single pair (both parents were wild born). In summarizing the features of one of these hybrids, Wolkin and Myers say (p. 216) that she was a mosaic of gibbon and siamang traits: "The hybrid had the black pelage of the siamang. The hair pattern of her head was similar to that of a siamang, whereas the pattern on her arm was clearly the same as the unusual patterns on a gibbon’s arm. Elements in her facial structure included the large eyes of a gibbon as well as the long, thin nose of a siamang…the siabon displayed the lengthy II-III digit webbing, but not the highly visible throat sac of the siamang." The chest was deep, the shoulders and hips wide, like a siamang, but the wrists, hands, ankles, and feet, slender, as in gibbon. Arms and legs were also proportionately shorter, as in a siamang, but the intra-membral index (arm-to-leg length ratio) was that of a gibbon. Kortlandt 1981; Myers and Shafer 1979; Pellicciari et al. 1988; Rumbaugh et al. 1976; Shaffer and Myers 1977; Wolkin and Myers 1980.
Hylobates pileatus [Pileated Gibbon] See: Hylobates concolor; H. lar.
Hylobates siki [Southern White-cheeked Gibbon] See: Hylobates gabriellae; Hylobates gabriellae × H. leucogenys.
Hylobates syndactylus [Siamang] See: Hylobates muelleri.
Nomascus siki [Southern White-cheeked Gibbon] See: Hylobates siki.
By the same author: Handbook of Avian Hybrids of the World, Oxford University Press (2006).
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