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Wild Dolphin Adopts Whale Calf In A World-First Case

In 2014, scientists noticed a bottlenose dolphin swimming with a calf that looked extremely strange -- eventually they realised the baby was a melon-headed whale, an entirely different species.

The dolphin mother had been swimming off the coast of French Polynesia in a group of 30 dolphins that researchers had been observing since 2009 as part of a long-term study.

She had already had one natural calf and the orphaned melon-headed whale (a male) was swimming alongside them in a trio, which was unusual enough in itself as dolphins normally care for only one calf at a time.

Melon-headed whales are actually a smaller species than bottlenose dolphins, growing to about three metres-long, while the dolphins can reach up to four metres.

Bottlenose dolphins. Source: Getty images.

The whale not only swam alongside the mother and her calf, competing with the dolphin's natural baby for attention, it began to behave like a dolphin in the wider family unit.

The young whale would regularly socialise with the juvenile dolphins and even learned to join in on their favourite recreational activity: leaping and surfing into waves.

In the journal article published describing the dolphin mother's behaviour, the researchers suggest that her personality and relative inexperience as a parent probably contributed to this strange situation.

READ MORE: Whale Dolphin Hybrid Discovered Off The Coast Of Hawaii

The successful integration of the whale calf into the wider social group also likely helped.

The mother made an enormous commitment to caring for the whale calf and they were spotted together for nearly three years.

Melon-headed whales. Source: Getty Images.

Their relationship continued long after her biological calf vanished for unknown reasons at one and a half years-old  and they only parted around the time the whale would have weaned.

Adoption is not unheard-of for related members of the same species, interspecies adoption is extremely rare.

The  only other documented case of this was a 2006 case of a group of wild capuchin monkeys who were found caring for a baby marmoset.

Adoption is considered a primarily human behaviour and cases such as these change the scientific understanding of the practice.

Melon-headed whales have been found to have other extremely unusual interactions with dolphins -- last year a baby 'wolphin' was discovered off the coast of Hawaii, the offspring of a male rough-tooth dolphin and a female melon-headed whale.