Changes in the Reproductive Condition of Female Gelada Baboons Following the Takeover of One-Male Units


Primate Research Institute, Kyoto University, Inuyama City, Aichi, 484 Japan.

Abstract and Summary

Takeover of a social unit is known to affect the reproductive condition of the females of some primate species as a result of infanticide. Gelada females, however, come into oestrus even though infanticide does not occur. Although females with very young infants do not undergo a change in reproductive state, pregnant females will usually abort their foetuses even though these may be nearly full term.

Following the takeover of a one-male unit, most gelada females show their acceptance of the intruding male quite soon after his initial approach by presenting to him, after which he mounts them. Bond formation between the new male and the females goes through a series of behavioural stages that culminate in copulation. In contrast to other species, infanticide by the new male was not observed. The former harem male remains in the unit as a follower, though without sexual access to the females. The order in which the females come into oestrus is not significantly correlated to their dominance ranks. Females with infants of 6–24 months old come back into oestrus much sooner than expected after a takeover; females with younger infants seldom come back into oestrus. Five abortions were observed following the takeover of 3 units; the females in question subsequently came back into oestrus and mated with the new male. It is suggested that females probably balance the cost of wasting the investment in an offspring against the risks of failing to bond with the new male.