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Key Words
Food sharing * Hylobates lar * Gibbon * Parental care
Introduction
Food sharing has been reported for only a few genera of primates, with rather few observations concerning wild animals [for a review, see 1]. It is well documented in the Callitrichidae where adult and non-adult group members help carry the infants [2] and in monogamous cebids [3]. In Leontopithecus rosalia and Callithrix flaviceps food possessors gave `food calls' which solicited immature group members to take the food [4, 5]. Food transfer is also common in chimpanzees (Pan troglodytes) where mothers share food with their offspring, particularly when it is difficult for the young to obtain and manipulate the foods independently [6, 7]. Male chimpanzees share food with each other [8], with females [1] and with infants; they are more likely to engage in the latter than are unrelated females [9].
In captive gibbons, food sharing is not infrequent [10-14] but has been observed only rarely in the wild [15, 16]. Furthermore, gibbons apparently rarely share food voluntarily [11, 16] although two cases of this were reported for captive siamangs by Orgeldinger [14].
Seven incidents of food transfer are documented in this paper, during a 14-month study of three wild groups of Hylobates lar in Khao Yai National Park, Thailand, and possible explanations for the conspicuous difference in frequency with which it occurs in captivity and in the wild are discussed.
Study Site and Methods
The gibbon study area of Khao Yai National Park (14 deg.5-15' N, 101 deg.05-50' E) lies within an extensive block of primary seasonal evergreen forest; it is described further in Raemaekers et al. [17]. Three neighbouring family groups of lar gibbons (referred to as A, B and C) are fully habituated to human observers.
At the time of the study, groups A and C each contained 2 adults and 3 male offspring. These were classified as subadult (both about 8 years), juvenile (both about 5 years) and older infants (both about 2 years). Group B contained an adult female and 2 adult males. The younger of these adult males was a subadult in group C who immigrated to group B in early 1994 [W.Y. Brockelman, pers. commun., 1994]. In addition, group B contained a subadult female (about...