Researchers from the Far Out Ocean Research Collective were surprised earlier this month to spot a female bottlenose dolphin swimming off the shore of Paihia, New Zealand, with a pilot whale calf in tow. Far from lost, the young whale appeared to be interacting with the female bottlenose like mother and baby, indicating that the little one has been adopted. Apparently, the unusual cross-species interaction has precedent.
“Bottlenose dolphins are known to adopt or 'acquire' calves of other species,” wrote researcher with the collective Jochen Zaeschmar in an email to IFLScience. “There are several records from around the species' range. However, adopted calves are usually of species that are the same size or smaller than bottlenose dolphins such as common dolphins. Apparently, there was at least one other case of a pilot whale calf adoption in the Strait of Gibraltar. It was still a surprise to us, though."
Tissue-clutching-stuff it may seem, Zaeschmar says such calf acquisitions aren’t necessarily the altruistic acts they appear to be. Bottlenose dolphins have been known to steal calves, though arguably without malice aforethought as it’s likely the result of misplaced maternal instinct. In a Facebook post, the collective reported that the adoptive mother had been spotted in a mixed group of false killer and pilot whales, which could well be where she picked up the wee calf.
Fortunately, such species mixing is not uncommon in the waters off New Zealand so it’s possible the calf could get picked up by its birth parents or others of the same species in the coming months. Adoptions like these, Zaeschmar explained, usually don’t stretch beyond a few months – and given the pilot whale will get very big compared to a dolphin calf, it will eventually need more milk than its bottlenose mother can provide.
“The two are highly likely to associate with pilot whales again and maybe the calf can be reunited with its own species, if not its birth mother,” wrote Zaeschmar. “Pilot whales rear their calves communally, which means that even females without their own calves may lactate.”
An awkward accidental kidnapping, maybe, but pilot whales and bottlenose dolphins are said to get on well, with the collective not yet having observed any interspecies aggression between the two groups, who are together in 50 percent of the pilot whale encounters they have observed.
As the odds are in favor of the young whale’s return to its native species, the collective doesn’t need to monitor the situation. Zaeschmar says they’re hoping to spot the pair again, but given bottlenose dolphins move further offshore in winter they might not make an appearance until next spring. The adoptive mother is well-known to the collective, who have been recording encounters with the dolphin since 2005.
Though New Zealand does see mass-strandings of pilot whales, the species currently appear to be doing well in the region. Their biggest threats largely hinge on pollution and the climate crisis, which could push out their main food source of squid. “The best thing people can do to help pilot whales and other cetaceans is to be mindful of their consumer habits that may have detrimental effects on marine life and its environment,” said Zaeschmar. “Be informed about the impacts of your actions and adjust your lifestyle choices accordingly.”