Parents and Offspring

Parent-Offspring Bonds

The mother and infant gibbons have a very strong bond, which is likely the result of the infant’s high dependence on the mother for the first year or two (Islam and Feeroz 1992). After clinging to the mother’s chest for the first year, the infant gradually spends time moving on its own (Islam and Feeroz 1992). The female and older offspring are involved in grooming the infant, while the male rarely takes part (Islam and Feeroz 1992). Infants have a much weaker bond with their fathers and take more time to warm up to them (Islam and Feeroz 1992). The male’s primary parental investment is his defense of the territory (Raemaekers and Raemaekers 1985). Leighton (1986) notes that in performing the dangerous and energetically costly task of defending the territory, the male enhances his reproductive success as a result of his mate’s decreased efforts in taking care of the infant and the territory. Siamang fathers, however, invest much more in their offspring than males of other gibbon species, often carrying and playing with the infants in addition to defense (Leighton 1986).

Click here for images of a newborn gibbon and mother.

Photograph courtesy of S.P. Flannery <http://members.tripod.com/cacajao/index.html>

Helping Behavior

Subadults may be allowed to stay in the natal territory a few years after reaching maturity if they serve as helpers in the territory (Brockelman et al. 1998). These subadult helpers perform roles such as grooming, playing with younger siblings, and aiding in territorial defense (Brockelman et al. 1998). These behaviors benefit the younger offspring, helping them develop physically and socially as a result of play and grooming and benefit the parents in that less time and energy must be devoted to territorial defense and playing with younger offspring (Brockelman et al. 1998).

Subadult helping appears as though it might be altruistic, but it is ultimately a selfish behavior. Subadult helpers can gain experience raising young, which will increase their reproductive success later. They can also stay in the natal territory where they are safe while looking for possible solitary individuals of the opposite sex nearby (Reichard and Sommer 1997). By helping their younger siblings become healthier and stronger, helpers also increase their own indirect fitness.

The most important benefit to the subadult helper is the possibility of parental aid in gaining a territory (Tilson 1981). Parents will often either escort the subadult into an available territory, help intimidate others in a nearby territory by numbers, or take over part of neighboring territory and give it to the subadult (Tilson 1981). Having a territory increases the chance of a subadult finding a mate and becoming reproductively successful (Tilson 1981). Thus, helping a subadult is a part of the gibbon’s parental care strategy because in helping the subadult achieve reproductive success, the parents also maximize their own reproductive success (Tilson 1981).