Dielentheis, T.F.; Zaiss, E. & Geissmann, T., 1991: Infant care in a family of siamangs (Hylobates syndactylus) with twin offspring at Berlin Zoo. Zoo Biology 10: 309-317.

Infant care in a family of siamangs (Hylobates syndactylus) with twin offspring at Berlin Zoo

Thomas F. Dielentheis¹, Elke Zaiss¹ & T. Geissmann^2
1Division of Human Biology, Freie Universität Berlin, West Germany
²Anthropological Institute, University Zürich-Irchel, Switzerland

Key words: Paternal care; helping behavior; multiple offspring; gibbon.

Abstract: Infant-carrying in a family group of siamangs with twin offspring was observed during a 2-week period. The twins were about 11 months old at the time of the study. One or both twins were usually carried by their father, but hardly ever by their mother. A considerable amount of infant-carrying was also contributed by the twins' juvenile brother. Helping behavior (defned as the care of offspring by individuals who are not their parents) is not normally known to occur in siamangs or other hylobatids. We suggest that the presence of multiple offspring may have facilitated the occurrence of infant-carrying exhibited by a non-parental family member. This finding may point to one of the mechanisms influencing the occurrence of helping behavior in general.