Interspecies adoption is extremely rare for wild animals. Only one case of a wild mammals adopting an infant from a different species was ever documented (a group of capucins adopting a marmoset) before scientists from the Groupe d’Etude des Mammifères Marins (GEMM) confirmed that a dolphin mom adopted a melon-headed whale calf in the coastal waters of French Polynesia. This is the first ever documented case of interspecies adoption for marine mammals.

The study, published in Ethnology, details how the bottlenose dolphin mom cared for a young melon-headed whale from 2014 to 2018. This is an even stranger phenomenon considering the dolphin already had a biological baby, and dolphins usually only care for one calf at a time.

The study claims that the whale competed actively for the mother’s attention, rarely leaving her side. Although he didn’t socialize with the dolphin community as much as his adoptive sister, he did start to exhibit bottlenose behaviors, like surfing and jumping.

Although female bottlenose are sometimes known to kidnap the calves of other species, that is likely not the case here, since the mother already had her own biological offspring.

According to Pamela Carzon, one of the leading scientists involved in the study, “It is very difficult to explain such behavior, especially since we have no information on how the melon-headed whale newborn was separated from his natural mother.”

The biological female calf disappeared at about one-and-a-half-year-old for unknown reasons, but the adopted melon-headed calf stayed for several years by her side before being weaned and later expulsed from the dolphin group “in a rather brutal fashion,” explained GEMM.