Scientists have long thought humpbacks loners. New research shows this isn’t so: Researchers have observed some female whale form friendships that last for years. The behavior has only been observed in lady humpbacks of similar age, with the whales going their separate ways during the breeding season, but reuniting in the open ocean each summer. These bonds can be quite strong: the longest association endured for six years.

The study appears in the journal Behavioral Ecology and Sociobiology, and it also found that the whales with the longest-lasting associations gave birth to the most calves–another animal kingdom example that friendship is beneficial. The whales are probably improving their feeding efficiency, suggests lead author Christian Ramp.

“Staying together for a prolonged period of time requires a constant effort. That means that they feed together, but likely also rest together…. So an individual is adapting its behaviour to another one.” [BBC]

When categorizing fraternal sea animals, scientists used to make a dental distinction: tooth-sporting sperm whales, dolphins, and orcas make friends, but baleen whales like the humpback–those whales that use stringy baleen to strain their food out of the water–were thought less social. Says Ramp:

“I was very surprised by the prolonged duration…. I was expecting stable associations within one season, not beyond. I was particularly surprised by the fact that only females form these bonds, especially females of similar age.” [LiveScience]

Snapping pictures of yearly whale visits to the Gulf of St. Lawrence off Canada’s coast since 1997, scientists including Ramp recorded the familiar groupings. As for where the summering whales meet up and how they recognize their old friends, those things are still mysterious.

Ramp wonders whether whaling has made humpbacks’ social pairings increasingly rare since traveling together might make them easier targets, though he says he would need more research to make this conclusion.

Related content:
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80beats: Primitive Proto-Whales May Have Clambered Ashore to Give Birth
80beats: Is the Whaling Ban Really the Best Way to Save the Whales?
Discoblog: Should Dolphins and Whales Have “Human Rights”?

Image: flickr / NOAA’s National Ocean Service