Sperm Whales Adopt Deformed Dolphin_Featured_, Animals, Pets, Wildlife Wednesday, January 23rd, 2013
(ScienceMag.org) Sperm whales are fierce squid hunters, but they also have a softer side. In a serendipitous sighting in the North Atlantic, researchers have discovered a group of the cetaceans that seem to have taken in an adult bottlenose dolphin with a spinal malformation, at least temporarily. It may be that both species simply liked the social contact.
Creatures form “friendly” connections with members of other species throughout the animal kingdom. These often short-lived relationships can offer increased protection from predators and more effective foraging. Some particularly unusual alliances illustrate that they can also satisfy a social craving. For example, the signing gorilla Koko had a pet cat named All Ball; in a Kenyan nature park, a hippopotamus, Owen, grew close to a giant tortoise, Mzee.
Among ocean-dwelling mammals, dolphins are perhaps the most gregarious. They’ve been spotted traveling, foraging, and playing with a wide variety of other animals, including many whales. On the other hand, as far as the authors of the forthcoming paper in Aquatic Mammals know, sperm whales had never been reported cozying up to another species. Specialized deep-water hunters who travel great distances, the whales are more timid than dolphins and harder for people to observe.
Indeed, behavioral ecologists Alexander Wilson and Jens Krause of the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin did not expect to find a mixed-species group when they set out to observe sperm whales (Physeter macrocephalus) some 15 to 20 kilometers off the island of Pico in the Azores in 2011. But when they got there, they found not only a group that included several whale calves, but also an adult male bottlenose dolphin ( Tursiops truncatus). Over the next 8 days, they observed the dolphin six more times while it nuzzled and rubbed members of the group (see slideshow). The sperm whales seemed to at least tolerate it; at times, they reciprocated. “It really looked like they had accepted the dolphin for whatever reason,” says Wilson, who was snorkeling nearby. “They were being very sociable.”
The researchers could be sure that the bottlenose dolphin was the same one each time because it had a rare spinal curvature that gave its back half an “S” shape. Although the dolphin seemed otherwise healthy, that probable birth defect could be the key to understanding its attachment to the sperm whale group. Very few predators stalk the Azorean waters, so they doubt that it needed the whales for protection. But they speculate that the malformation could have put the animal at a disadvantage among its own kind. Perhaps it couldn’t keep up with the other dolphins or had a low social status…
Image: Alexander D. M. Wilson/Aquatic Mammals