Death in dolphins: do they understand they are mortal?

From New Scientist: Death in dolphins: do they understand they are mortal?
REPORTS of dolphins interacting with dead members of their pod are raising questions about whether cetaceans understand the concept of death. Bottlenose dolphins in western Greece have been seen reacting to death differently depending on whether a pod member has died suddenly or after a longer period of illness, New Scientist has learned.

Interpreting animal behaviour after the death of a companion is fraught with difficulty. Death is rarely observed in the wild, and it is easy to erroneously attribute human emotions to animals. Nevertheless, several species of intelligent, social animals, such as gorillas, chimps and elephants can display particular behaviours when an animal dies - behaviours which some have interpreted as akin to mourning. Taken together with a growing number of reports of cetaceans interacting with dead animals and the discovery that they have specialised neurons linked to empathy and intuition, the Greek study suggests dolphins may have a complex - and even sophisticated - reaction to death.

Joan Gonzalvo of the Tethys Research Institute based in Milan, Italy, has been observing the bottlenose dolphin (Tursiops truncatus) population in the Amvrakikos gulf since 2006. In July 2007, he and his team of Earthwatch Institute volunteers saw a mother interact with her dead newborn calf. She lifted the corpse above the surface, in an apparent attempt to get it to breathe. "This was repeated over and over again, sometimes frantically, during two days of observation," says Gonzalvo. "The mother never separated from her calf." The team heard her calling to it while she touched it with her snout and pectoral fins.

The newborn had a large bruise on its lower jaw, suggesting it may have been killed by another dolphin. "Infanticide has been reported in this species," says Gonzalvo. Aware of the dangers of investing animal behaviour with human emotions, he nonetheless suggests the mother may have been mourning the sudden death: "[She] seemed unable to accept the death."

Release from suffering?
One year later, Gonzalvo came across a pod surrounding a 2 to 3-month-old dolphin that was having difficulty swimming. It bore bleach marks, possibly from exposure to pesticide or heavy-metal pollution. "The group appeared stressed, swimming erratically," he says. "Adults were trying to help the dying animal stay afloat, but it kept sinking." It died about an hour later.

From his previous observation, Gonzalvo expected the mother to stay with the corpse. Instead, it was allowed to sink and the group immediately left the area. "My hypothesis is that the sick animal was kept company and given support, and when it died the group had done their job. In this case they had already assumed death would eventually come - they were prepared." Gonzalvo accepts that his interpretation is speculative and based on limited data. He is gathering examples from other researchers before publishing his observations.

Ingrid Visser of the Orca Research Trust in Tutukaka, New Zealand, has seen bottlenose dolphins and orcas carrying dead infants in what she too interprets as grief. She acknowledges that the activity may simply be misdirected behaviour, and that the animals do not know that the calf is dead. "But we do know that cetaceans have von Economo neurons, which have been associated with grief in humans." As a result, she speculates that the behaviours are a form of grief.

Death rites
Visser has seen similar things at pilot whale strandings. "When one died the others would stop when passing by, as if to acknowledge or confirm that it was dead. If we tried to get them to move past without stopping, they would fight to go back to the dead animal. I do not know if they understand death but they do certainly appear to grieve - based on their behaviours."

Karen McComb of the University of Sussex, UK, who has studied how elephants act when they find elephant bones, says Gonzalvo's observations bring to mind other intelligent, social mammals, but it is impossible to know what is going on in an animal's mind.

"It is fascinating but out of our reach as scientists," she says, adding that any inferences are necessarily speculative. "It's great to accumulate examples though - as more are gathered a clearer picture emerges."