How Sperm Whales Sleep

A team led by Luke Rendell at the University of St Andrew’s, UK, were monitoring calls and behaviour in sperm whales (Physeter macrocephalus) off the northern Chile coast when they accidentally drifted into the middle of a pod of whales hanging vertically in the water, their noses poking out of the surface. At least two of the whales were facing the boat, but not a single animal responded.

β€œIt was actually pretty scary. The boat had drifted into the group with its engine off [while] I was below decks making acoustic recordings,” says Rendell. β€œOnce I saw the situation I decided the best thing to do was to try and sail our way out of the group rather than turn the engine on and have them all react.”

The researchers was almost successful, but unfortunately they nudged one of the whales on the way out. β€œWe had no idea how they would react; each of the animals probably weighed up to twice as much as our boat, and could have sunk us. If they had decided to take action collectively β€” sperm whales do engage in communal defence [against] killer whales β€” then we could have been in real trouble,” Rendell says. Fortunately for everyone on board, after an initial jolt of activity the whales timidly moved away, and within fifteen minutes were bobbing peacefully at the surface again.