Social correlates of reproductive success in the Gibbon colony on Ko Klet Kaeo, Thailand

Abstract

The free-ranging colony of gibbons established on an island in the Gulf of Thailand by the SEATO Medical Research Laboratory in 1966-1967 was terminated in 1970. Out of the 20 gibbons originally introduced, four adults of each sex remained until near the end of the project. The four females each gave birth to one infant. In all cases the young were conceived five or more months after pairbonds and ranges had stabilized into a more natural-like pattern, with fairly regular morning inter-group vocal sessions and territorial boundaries between groups containing the most feral individuals.The maximum effective breeding density on the 60-acre island was found to be about four or five pairs. The chances of reproductive success appear to be maximized in a free-ranging colony containing several pairs by maintaining a one-to-one sex ratio and allowing enough space so that natural patterns of social behavior may be expressed. The amount of area required per group may vary with the individual gibbons and the environment, but we found it to be about ten acres.The SEATO Medical Research Laboratory in Bangkok, in collaboration with the Delta Regional Primate Research Center, Covington, Louisiana, established a colony of free-ranging gibbons (HyZobates Zar) on

A glut of gibbons in Sarawak – is rehabilitation the answer?

“…Aggressive behaviour towards other gibbons and humans was common, as was a tendency by some animals to walk along paths rather than remaining arboreal. Home ranges did not cover the full extent of the island (Berkson et al, 1971;Brockelman et al, 1973).…”

Family Formation Strategies of Kloss’s Gibbons

“…Another possible way in which new gibbon groups may form is for a subadult offspring to replace its like-sexed parent upon death or senility [Carpenter, 1940] or for a transient subadult to replace an aged or injured adult in an existing family group [Brockelman et al, 1973;. During this study a subadult male replaced his father, missing after a hunting party of aborigines had camped overnight near this group's sleeping tree.…”

“…Brockelman et al [1973] suggest that the establishment and maintenance of a territory play a major role in the subsequent reproductive success of paired gibbons. But, because of the long period of waiting required before young adults can find sufficient space, replacement of an adult may be a more expedient strategy.…”

Territory and Monogamy Among Kloss&rsquo; Gibbons (<i>Hylobates klossi</i><i>i</i>) in Siberut Island, Indonesia

“…Some white-handed gibbon families living in isolated patches of forest and others introduced onto a small island reproduce in home ranges only 4-6 ha in area [Berkson et al, 1971;Brockelman et al, 1973Brockelman et al, ,1974, which is com parable to H.klossii territories (table I). The large territories of whitehanded gibbons and siamangs (table I) might be artifacts of the human dis turbance described above.…”

“…172,214,220,224-226;Ellefson, 1974;Chivers, 1971;Brockelman et al, 1973Brockelman et al, ,1974D elacour, 1933]. Intrasexual territorial aggression may be the proximal basis of monogamy in all gibbons.…”