First-year sperm whale calves echolocate and perform long, deep dives

Deep-diving sperm whales have a complex social structure and the largest brain of any animal, but very little is known about the ontogeny of their diving, foraging, echolocation, and communication skills. In large-brained terrestrial species, social skills develop earlier than locomotor abilities, but this may not be feasible for sperm whales, which require locomotor skills from birth to breathe, swim, and suckle. Here, we shed new light on the relative development of social and locomotor capabilities of a wild toothed whale. Sound and movement recording tags deployed on three first-year sperm whale calves for a total of 15h revealed that these calves rarely produced codas for communication with adult whales, but likely tracked the ample passive acoustic cues emitted by clicking adults. The calves' diving capabilities were well developed (maximum dive depth: 285, 337, and 662m; maximum dive time: 11, 31, and 44min) and they all produced clicks in a way that is consistent with echolocation. The calf performing the longest and deepest dives additionally emitted two echolocation buzzes, suggesting that it could haveattempted to forage. Thus, sperm whale calves may supplement their milk diet with food caught independently at depth much earlier than previously believed. Contrary to terrestrial mammals, we propose that the maturation of locomotor, diving, and echolocation skills may be favored over investment in developing social communication skills at an early age in sperm whales.Significance statementThe life of deep-diving toothed whales has up until recently been a mystery and the understanding of their behavior has generally been limited to surface observations and captive studies. Fortunately, the rapid development of animal-borne bio-logging devices has markedly improved our knowledge of the behavior of adult whales. The behavior and development of young calves are, however, still largely unknown. Sperm whale calves are challenged by being air-breathing marine mammals, which must learn to hunt prey at great depths. Using Dtags, we here show that sperm whale calves have much more pronounced diving capabilities than previously thought. The onset of independent foraging and foraging effort seems linked to the diving capability of the calf. These results show that young members of this otherwise slowly maturing species of apex predators do learn to dive and may hunt much earlier than previously believed.