Reproductive intervals in captive female western lowland gorillas with a comparison to wild mountain gorillas

A wide disparity between parturition and the resumption of sexual behavior in two captive female western lowland gorillas prompted an investigation of interbirth intervals (IBIs) in captive western lowland gorillas that had reared their infants. To determine reproductive intervals, a questionnaire was sent to 30 institutions (19 in North America and 11 in Europe) that maintained captive females who had previously reared or were currently rearing their offspring. Information compiled relates to the length of reproductive intervals, including lactational anestrus, estrous behavior to conception and from parturition to conception, and IBIs. These data are compared with studies published on wild mountain gorillas. The median IBI for 16 mothers still rearing infants when their next conception occurred was 4 years (range 2.33-6.42 years, N = 16). Twenty-one percent of the 52 mothers in this study are no longer reproducing. The mean time without reproduction since separation from their last offspring was 5.43 years. This study indicates that the length of IBIs, lactational anestrus, and intervals from parturition, separation, and estrous behavior to conception compare closely with findings for wild populations. Incompatibility between partners may be a factor limiting further reproduction in some captive mothers in this study.