Who Cares? Between-group variation in alloparental caregiving in sperm whales

Although the details of the various systems of allocare in primates, rodents, and carnivores have been well described, little is known about the existence of alloparental care in cetaceans. It is believed that the matrilineal social organization of the sperm whale functions to provide vigilant allomothers for calves at the surface while mothers make deep dives for food. Sperm whale females do have a system of allocare, but details are unknown. This study aimed to elucidate sperm whale allocare, in particular: who escorts whose calf and whether or not calves suckle from nonparent females. Using photo identification and behavioral calf follows, we examined patterns of adult-infant interactions for 23 sperm whale calves in the Sargasso and Caribbean Seas. Although multiple individuals of both sexes escorted the calves, the system of escorting differed between the 2 sites. For all calves studied in the Caribbean, we found that 1 female provided most of the allocare but did not nurse the calf, whereas in the Sargasso, multiple females provided care for, and nursed, the young. We discuss differences between populations that may have resulted in the observed differences in these 2 systems of allocare and how these findings fit with current hypotheses on the roles of kin selection and reciprocal altruism in cooperative care in mammals.