An Overdose of Coolness

Chelsea Wald explains yet another cool mammalian surprise:

Photo by Alexander D. M. WilsonSperm 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 ….

…. 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. 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 dolphin itself was easy enough to recognize for its unusual spinal curvature. While low predation rates in the Azores suggest the interspecies partnership is not for protection, it is possible that the dolphin’s spinal issue caused it some trouble with its own species. “Sometimes some individuals can be picked on,” explained Wilson, suggesting some alienation within its own social group. While the dolphin can keep up with sperm whales, and may eventually play a role in the group’s behavior, the question remains as to what the whales get from the relationship. Cetacean ecologist Mónica Almeida e Silva called the relationship “puzzling”, and behavioral biologist Luke Rendell suggested it’s too early to read deeply into this seemingly unique example of cross-species socialization.

And caution is wise, as there is always a risk of overdosing on this kind of coolness.