More than six species of the marine mammals have been observed clinging to the body of a deceased conspecific, probably a podmate or relative, and kept vigil over a dead companion.
A study by researchers from University of Milano-Bicocca describes observations of adults carrying dead calves and juveniles in 7 toothed cetaceans (odontocetes). The observation was based on 14 events from 3 oceans. The seven species studied were Indo-Pacific bottlenose dolphins, killer whales, Australian humpback dolphins, sperm whales, Risso’s dolphins, short-finned pilot whales, and spinner dolphins.
All species showed the same gesture toward a deceased companion. Although they can’t determine for sure the cause behind this behaviour, study co-author Melissa Reggente told National Geographic that the only possible explanation for such behavior is "grief."
Mourning a dead companion is a time intensive and costly action, which takes away from animals finding food, mating, and creating interactions with other live animals – so it doesn’t make much sense from an evolutionary perspective. Which is why the researchers concluded that they’re likely to be genuinely grieving.
The study also identified several ways whales mourn for their dead ones. For example, some touch their dead companions using their fins, while some circle around their dead as if guarding them so other species would not feed on their dead body.
Whales are highly sociable species. Studies showed that they form actual friendships, even lifelong bonds with their companions. Some researchers have observed that whales, even after years of migrating and breeding, return to meet their companions each year. The study corroborate that adults mourning their dead young is a common and globally widespread behavior in long-lived and highly sociable and cohesive species of mammals.
Animal researchers have traditionally been apprehensive about attributing human emotions to other animals for fear of being anthropomorphic. But observations of animal behavior over the last few decades have made the attribution of deep emotion to some animals difficult to deny.