Infanticide reduces the reproductive success of both parents, but it can increase the reproductive success of the infanticidal male if three conditions are met: there is a low probability that the infanticidal male sired the infant, the mother resumes reproduction sooner if the infant is killed, and the mother is likely to mate with the infanticidal male (Hrdy 1977 Smuts and Smuts 1993).įemale primates have developed several strategies to avoid infanticide, such as forming permanent associations with males that provide protection against other males, remaining with the father until weaning the infant, residing in a multi-male group, mating with multiple males to create paternity confusion, or joining a better protector male using secondary dispersal (Palombit 2015). in rodents, ungulates, carnivores, pinnipeds and primates (van Schaik 2000a). One clear example of sexual conflict suffered by reproductive females is infanticide by males (Lukas and Huchard 2014), which has been observed in a wide range of mammals, e.g. Social mammals exhibit a range of intersexual conflicts and compromises (Clutton-Brock 2007). These observations highlight the behavioural plasticity shown by female gorillas in response to sexual coercion by males. To our knowledge, these observations are the first to show that wild female western lowland gorillas can transfer voluntarily while pregnant without incurring infanticide by a new silverback. The females gave birth 5–6 months (gestation period 8.5 months) after their last transfer. The gorillas were observed from 1995 to 2015 at the Mbeli Bai research site in northern Republic of the Congo. We report here on three adult females that transferred voluntarily while pregnant multiple times between two groups yet their offspring were not killed by the new group’s silverback. In the few known cases of female gorillas transferring when pregnant (mainly after group disintegration), their offspring were killed. If females are pregnant or have unweaned offspring when the only male in the group dies, their offspring are vulnerable to infanticide by the new silverback that they join (via involuntary dispersal). By doing so they leave a weaker silverback near the end of his tenure and join a stronger silverback at an earlier stage of his own tenure, thereby mitigating the risk of infanticide if the former dies. Female gorillas have developed the rare strategy of secondary dispersal in which they transfer between reproductive groups during the limited time period between weaning an infant and conceiving the next one (voluntary dispersal). However, while Nadiri periodically touched her baby just after giving birth, she never picked up her newborn the first day,” says Ramirez.In many social species, after the alpha male has been replaced or the group disintegrates, a female’s infant is at risk of infanticide by a male. “We had worked with Nadiri to prepare for this moment and were optimistic this time around that Nadiri would pick up her baby and show maternal care. The new mom’s maternal instincts eventually engaged and Yola was reunited with her mom and the other members of her family. Therefore, Yola spent the first several months of her life under round-the-clock care by gorilla keepers and veterinary staff while having daily interactions with her mom. Because Nadiri was partially human-raised as an infant and had no experience as a mom, she did not know what to do when she gave birth. In 2015, Nadiri gave birth to her first offspring, Yola, who was sired by Vip. The newborn is the second baby for 24-year-old Nadiri and the first between her and dad, 21-year-old Kwame. By doing short introduction sessions frequently throughout each day, we hope her maternal instinct will soon kick in.” She is staying close and has picked up her baby for short periods over the weekend, but has not shown any interest in nursing her. “We will continue to introduce Nadiri to her baby. Nadiri has visual, auditory and olfactory contact with her baby. “We will continue to provide hands-on care while keeping the baby in close proximity to Nadiri 24/7 and attempting to reintroduce her to mom,” says Martin Ramirez, mammal curator at Woodland Park Zoo. The first 72 hours of life are the most critical for a newborn gorilla. Staff are nourishing the baby by bottle feeding her human infant formula, keeping her warm and providing her with short visits with her mother the baby is doing well. Shortly after birth, zoo gorilla and veterinary staff had to step in and place the baby under round-the-clock care in the gorilla building because Nadiri had not picked up her baby to nurse or keep her warm enough the first day.
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