A humpback supergroup off the west coast of South Africa. Jean Tresfon/PLOSone

Over the past few years, humpback whales—normally solitary creatures—have been amassing in huge “super-groups,” surprised scientists report in a recently published article in PLOSone. At dozens of different times, crowds numbering from 20 to 200 whales have been spotted congregating off of the west coast of South Africa.

“It’s quite unusual to see them in such large groups,” whale researcher Gísli Vikingsson told New Scientist. South Africa is also much further north than the whales usually venture in the summer—normally, they’re way down south in the Antarctic.

If humpbacks usually like their privacy, why are they clubbing up like this? As New Scientist reports, experts are unsure—but they have a few ideas. Unlike many species, humpbacks have been doing pretty well over the past few decades, recovering from a severe whaling-age population dip. It might be that their increasing numbers are changing the availability of their prey. It could also be that they used to always have big parties like this, and now they finally can again.

A humpback says hey. Robbie Shade/CC BY 2.0

The question of what they do when they get together is slightly easier to answer. While a human super-group brings together various talented musicians from different bands, a whale super-group is more for feeding, the researchers explain. They can tell the whales are chowing down because of “repetitive and consecutive diving behaviors… and the pungent, ‘fishy’ smell of whale blows,” they write.

But some harmonizing is likely involved, too—these are whales, after all. I’m naming three of them Crosby, Krills and Splash.

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