Sperm whales blow bubbles to stay still while they sleep upright

Sperm whales sleep head-up, vertically — the only whales to do so. Their natural body oils and lung air make them float upward, so they release bubbles to stay at a steady depth while sleeping. Tagging data off Norway confirmed how this works. The study, from St Andrews and Neuchâtel, appeared in the Journal of Experimental Biology on July 23, 2026.