A bstract We describe a novel behavior, termed “tail‐up,” observed in humpback whales ( Megaptera novaeangliae ) on wintering grounds on Abrolhos Bank, Brazil. The behavior involves the whale positioned vertically in the water column with its tail in the air. With the exception of calves, tail‐up was observed in all social classes, and its frequency increased through the end of the season. Tail‐ups were recorded in 144 (5.8%)...