Extra-pair Copulations in a Monogamous Gibbon (Hylobates lar)

This study, conducted in a rainforest in Thailand, presents the first evidence for extra-pair copulations in white-handed gibbons - Asian apes that live in monogamous groups. The ratio of in-pair copulations versus extra-pair copulations as observed among three free-ranging, well-habituated groups was 88 versus 12 % and involved one adult paired female and three adult paired males. Extra-pair copulations may be explained as an effort to breed with a partner of superior quality to the current mate and/or may be part of a strategy to forestall infanticide.