Do female bonobos (Pan paniscus) disperse at the onset of puberty? Hormonal and behavioral changes related to their dispersal timing

Natal dispersal is a milestone in an animal's life history, but its timing in developmental trajectories may differ between species. Although the two Pan species exhibit a similar pattern of female-biased dispersal, female bonobos (P. paniscus) leave their natal groups at an earlier age than female chimpanzees (P. troglodytes). As a preliminary step to explore the dispersal strategies of female bonobos, this study aimed to determine the relations of sexual swelling development, behavioral and hormonal activation, and first ovulation relative to dispersal timing. We measured levels of urinary estrone conjugates (E1C) and pregnanediol glucuronide (PdG) from 14 nulliparous females in wild bonobo groups at Wamba in the Democratic Republic of the Congo, and recorded their copulations with mature males. When close to dispersal, female bonobos exhibited swelling of the sexual skin (labia minora and perianal region) that did not reach the mature stage. Urinary E1C levels and copulation rates increased slightly before dispersal and greatly increased after dispersal. Ovulatory or gestatory signs implied by daily hormone profiles were not detected until one to two years after dispersal. Our findings indicate that female bonobos disperse at an early pubertal stage before ovulatory cycling is established. This earlier dispersal than sexual maturation could allow female bonobos to postpone reproduction-related energy costs until they become familiar with their new group or gain more time finding the group more suitable for successful reproduction in the future before actually settling. Further demographic and genetic data from dispersal to reproduction will help clarify their dispersal strategies.