In a mysterious change to their normal behaviour, humpback whales are forming massive groups of up to 200 animals. Humpbacks aren't normally considered to be terribly social. They are mostly found alone, in pairs, or sometimes in small groups that disband quickly. But research crews have spotted strange new social behaviour on three separate cruises in 2011, 2014 and 2015, as well as a handful of public observations from aircraft. These super-groups of up to 200 were spotted feeding intensively off the south-western coast of South Africa, thousands of kilometres further north from their typical feeding grounds in the polar waters of the Antarctic. "It's quite unusual to see them in such large groups," says Gísli Vikingsson, head of whale research at the Marine and Freshwater Research Institute in Iceland. Humpbacks mostly spend the summer in the polar regions of the Antarctic where the whales chow down on krill and build up fat stores. And winters are spent in the warmer waters of