Adoption is quite a rare phenomenon among the mammalian kingdom. In most documented cases of adoption in the wild it almost exclusively involves individuals of the same species. Until recently, the only scientifically acknowledged case of wild mammalian interspecies adoption was way back in 2006, where wild capuchin monkeys (Cebus libidinosus) adopted an infant marmoset (Callithrix jacchus).
This social accommodating behavior has once again recently been seen in mammals, not among primates but with cetaceans or toothed-whales. Led by Pamela Carzon of the Groupe d’Étude des Mammifères Marins (GEMM) de Polynésie, a study recently published in Ethology describes a unique instance of a cross‐genus adoption within a small community of common bottlenose dolphins (Tursiops truncatus) at the Rangiroa Atoll in French Polynesia. A foster female bottlenose adopted a young melon‐headed whale (Peponocephala electra) calf whilst she was already mothering her presumed biological offspring. The behaviour lasted over a period of three years and was especially surprising as bottlenose dolphins typically only care for a single calf at a time.
Bottlenose mom with her bottlenose offspring and adopted melon-headed calf (Pamela Carzon/Groupe d’Étude des Mammifères Marins (GEMM))
The study describes how this interesting relationship began when the male melon‐headed whale calf was around one-month old and presumably ended once weaned in April 2018. Oddly, Carzon and colleagues note the mother’s attachment to the bottlenose’s biological offspring was outlasted by her adopted melon-headed son. This seems to contradict our understanding of fitness as the adopted calf often competed for mom’s attention.
The authors hypothesize that the primiparous (bearing young for the first time) foster mother’s inexperience and personality may have been key factors resulting in this unexpected and non‐adaptive behavior. From observations they also suggest the very persistent male melon‐headed whale calf would frequently initiate and maintain a close association with the adult female bottlenose dolphin and this may have played a major role in the successful adoption. Amazingly, not only did this adopted calf develop a close relationship with his foster mom, but was also integrated into the family unit, and was observed exhibiting typcial bottlenose dolphin behaviours of jumping, surfing and socializing with other young male dolphins.
To learn more about the fascinating and rare relationship please see the full text at:
Carzon, P., Delfour, F., Dudzinski, K., Oremus, M., & Clua, É. (2019) Cross‐genus adoptions in delphinids: One example with taxonomic discussion. Ethology. 129: 669-676
