Off the coast of New Zealand, a group of marine biologists has discovered a mother bottlenose dolphin that had adopted a baby pilot whale.

The Kiwi-based Far Out Ocean Research Collective discovered the mammals sailing in the Bay of Islands in Northern New Zealand, and has now documented the pair on two separate occasions five weeks apart.

While it's not unheard of that dolphins adopt other species' babies, it's very rare to record the phenomenon with such a significant difference in species size. Bottlenose dolphins can reach 300 kilograms, which is no small fry—except that pilot whales can grow to two tons and reach six meters in length.

"She might have lost her own calf," researcher Jochen Zaeschmar told local reporters of the dolphin's behavior.

The Independent reported in 2019 that researchers in French Polynesia found a bottlenose dolphin that had adopted a melon-headed whale calf, and that the pair stayed together for three years.

Scientists don't know why exactly this happens, and hypotheses exist that it's misplaced mothering instinct—perhaps accentuated if a dolphin mother has lost her calf and finds a calf who has lost its mother. However the researchers in French Polynesia, pondering in their published paper on the finding, suggested it could be part of the mother's "personality," which is an endearing thought.

Regardless of what brings them together, these cases of adoption only last as long as the weening stage, as whales and dolphins hunting patterns are so different—and at that point the adopted whale makes it off into the world alone.

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