That’s one big baby! Bottlenose dolphin adopts pilot whale calf

June 23, 2021
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Most mixed families don’t include babies that will grow four times as big as their parents, but for a bottlenose dolphin mum who has adopted a pilot whale calf in the Bay of Islands, that may just be the case.

The Paihia-based Far Out Ocean Research Collective has documented the female bottlenose dolphin and her unusual offspring twice now, more than five weeks apart.

Researcher Jochen Zaeschmar said bottlenose dolphins had been known to adopt and nurse calves of other species in the past, usually closer-in-size common dolphins.

“It’s quite unusual to adopt a species that’s bigger than them.”

While bottlenose dolphins reached about 300 kilograms, fully grown pilot whales could weigh two tonnes, and grow to 6 metres in length.

Zaeschmar said no-one knew exactly why some dolphins adopted babies of other species, but suspected it was some kind of “misplaced mothering instinct”.

There was also the chance the baby pilot whale was calf-napped.

“She might have lost her own calf, but she also might also have decided she wanted a calf and stolen it.

“There is probably a very upset pilot whale mother out there somewhere.”

Luckily, he said the outcome was usually quite good for the inter-species dolphin families.

“Usually it only goes on for a few weeks. Most times it’ll rejoin its mother – they share the same range, so there’s a good chance it will bump into other pilots.”

There was a case in French Polynesia where a bottlenose dolphin adopted a melon-headed whale calf, and the family stayed together for years. The melon-headed calf even started adopting dolphin behaviour after a while.

Zaeschmar said the two species’ different eating habits might drive them apart after the calf stopped nursing, with pilot whales preferring to hunt for squid late at night.

“We’re really hoping to encounter them again … it’d be quite interesting after winter, when the calf would have really started growing.”

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