In 2014, scientists noticed a bottlenose mother was caring for a peculiar-looking male calf as well as her biological calf.
As they studied the trio, which were swimming in coastal waters off French Polynesia, they identified the orphan as a melon-headed whale, an entirely different species.
“We were really excited to be able to witness such a rare phenomenon,” Pamela Carzon, the study’s lead author and scientific leader of the Groupe d’Etude des Mammiferes Marins de Polynesie, told National Geographic.
“At the time we were really, really astonished.”
As Ms Carzon observed the dolphin family, they found the whale rarely left his adopted mother’s side.
Such a trio is rarely seen in the wild, as dolphin mothers typically care for only one infant at a time.
The whale also competed with its adopted sibling for attention and began to behave like the dolphins.
He would regularly socialise with other young dolphins and join them in surfing and leaping into waves.
In the study, published in the journal Ethology, the authors suggested the foster mother’s “inexperience and personality” may have contributed to the adoption.
They also said the adoptee’s “persistence in initiating and maintaining an association” with the adoptive mother “could have played a major role in the adoption’s ultimate success”.
The melon-headed whale and bottlenose dolphin mother stayed together for almost three years.
They stuck together after the mother’s biological calf vanished for unknown reasons at around one-and-a-half years old.
The adopted calf disappeared around the time he would have weaned.
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