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January 23, 2013

Sperm Whales Adopt Malformed Dolphin Into Their Group


Herman Melville’s Moby Dick may paint a picture of the sperm whale as a terrifying, ferocious creature that destroys ships and attacks the sailors on them, but modern research shows that sperm whales are compassionate and social creatures, dangerous only to the fish and squid that the giant whale feasts on for dinner, or to the orca whales that prey on sperm whale calves. A heartwarming and unusual recent discovery does even more to distinguish the sperm whale from its deadly reputation, as a group of sperm whales were observed “adopting” a bottlenose dolphin with a spinal malformation.

Behavioral ecologists Alexander Wilson and Jens Krause discovered this unique phenomenon when they set out to observe sperm whales off the island of Pico in the Azores in 2011. Upon arriving there, they discovered a whale group of adult sperm whales, several whale calves, and an adult male bottlenose dolphin. Over the next eight days, the pair observed the dolphin with the whales six more times, socializing and even nuzzling and rubbing members of the group. At times, the sperm whales seemed merely to tolerate the dolphin’s affection, while at others, they reciprocated. “It really looked like they had accepted the dolphin for whatever reason,” Wilson reports to ScienceNOW. “They were being very sociable.”

This gregarious dolphin was easily recognizable by its spinal malformation, a rare spinal curvature that gave the dolphin’s back half an “S” shape. This malformation did not seem to affect the dolphin’s overall health, but  was likely the reason that the dolphin joined up with the sperm whales in the first place. In the highly social and clique-based world of dolphins, such a disfigurement could have given the dolphin low social status, or may have prevented the dolphin from fitting in and keeping up with its peers. “Sometimes some individuals can be picked on,” Wilson says. “It might be that this individual didn’t fit in, so to speak, with its original group.” The deformed dolphin could perhaps better keep up with the sperm whales, which swim more slowly, and could stay by their side at all times, as sperm whales always assign a “babysitter” to remain at the surface with the calves while the other adults dive deep to feed.

While there are several likely possibilities for the dolphin’s advantage in the match, the whales’ reason for the adoption is less clear — there is no obvious advantage that the whales could gain by adding the dolphin to their group. Sperm whales have never been seen being affectionate to other species, and, further, scientists say that bottlenose dolphins and sperm whales often do not get along, as the dolphins have been known to chase and harass the whales and their calves.

It may be impossible to explain the reasoning for this unique match, and we should be careful not to “overread” the whales’ motivation as pity for the dolphin, says behavioral biologist Luke Rendell of the University of St. Andrews in the United Kingdom. Is it compassion, some kind of mutual protection, or simply a desire for social contact between the two species? An occurrence like this is too rare and too brief to understand in full. As Rendell explains, the whales might simply enjoy the dolphin’s attentions, or “they could just be thinking, ‘Wow, this is a kind of weird calf.’ “