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A dolphin has been spotted caring for a whale calf. It's the first known case of a wild bottlenose dolphin adopting a calf from another species.

Scientists observed the dolphin caring for the young melon-headed whale over a period of more than three years in coastal waters off French Polynesia in the South Pacific Ocean.

The whale calf is a completely different species to the dolphin which adopted it.

The dolphin already had its own baby, when it adopted the orphan whale.

According to Pamela Carzon, lead scientist from the Marine Mammal Study Group, said dolphins usually only have one calf at any one time so it is very rare for them to take on another.

It's also very unusual for wild mammals to adopt, especially when it's a different species.

Carzon and her team filmed and photographed the family from land and on boats as part of a long-term study of a community of around 30 bottlenose dolphins.

The melon-headed calf rarely left the dolphin mum's side and the three were frequently seen swimming together.

After a while, the whale calf started fitting in with his adopted family.

"The melon-headed whale was behaving exactly the same way as bottlenose dolphins," says Carzan writing in the biology magazine, Ethology.