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Sperm whales adopt deformed bottlenose dolphin

In 2011, behavioral ecologists Alexander Wilson and Jens Krause of the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin found a mixed-species group of sperm whales, including several whale calves and an adult male bottlenose dolphin. They located this unusual group approximately 15 to 20 kilometers off the island of Pico in the Azores.

For more than a week, Wilson and Krause observed the dolphin while it nuzzled and rubbed members of the mixed-species group. They noted that the sperm whales seemed to be okay with the attention from the deformed dolphin.

“It really looked like they had accepted the dolphin for whatever reason,” said Wilson, according to the journal Science. “They were being very sociable.”

According to an article appearing in the journal Science, the adult male bottlenose dolphin had a rare spinal curvature that formed its back half into an “S” shape. The behavioral ecologists contend that the deformity could be the key to understanding its attachment to the sperm whale group. While the researchers ruled out the need to use the whales for protection because of the lack of predators in the region, they believe that the deformity could have made the dolphin an outsider among its own kind, perhaps also preventing it from swimming at the same speed as the other dolphins.

“Sometimes some individuals can be picked on,” says Wilson. “It might be that this individual didn’t fit in, so to speak, with its original group.”

Researchers aren’t exactly sure why the sperm whales seemed to accept the bottlenose dolphin into their pack. Wilson said that there is no clear benefit for the sperm whales to allow the dolphin to swim among them.

Mónica Almeida e Silva of the University of the Azores in Portugal said she is having trouble finding an explanation for the sperm whales’ behavior because bottlenose dolphins have been known to chase and harass whales and their offspring.

This isn’t the first case of a larger animal adopting a smaller animal. According to ABC News, an elderly western lowland gorilla at the Erie Zoo in Pennsylvania named Samantha adopted a Dutch rabbit named Panda. Samantha had been living alone in her enclosure for seven years after her male companion passed away in 2005. Panda was slowly introduced to Samantha’s cage and eventually the large gorilla started sharing food with her tiny rabbit friend.

Why would sperm whales accept a dolphin into their group? Share your ideas in the comments section.

Photo credit: Alexander Wilson and Aquatic Mammals.