Do animals mourn their dead?

Examples of grief-like behavior abound in the animal world. Crows, which form lifelong pair bonds, flock to the bodies of their deceased, diving and swooping and emitting a call that summons other birds.

There are accounts of chimps and other primates refusing to put down the bodies of dead babies and holding onto them for days, even after decomposition has begun. In one case in Guinea, a mother carried her baby for 68 days. Scientists have observed bonobos pounding the chests of their dead, elephants lingering by the bodies of deceased herdmates, and cats and dogs refusing food when a fellow pet dies.

Other mammals also appear to grieve the loss of loved ones. Whales are known to carry around deceased calves after they die. One orca whale mother — known as Tahlequah — took this to the extreme, carrying her dead calf for 17 days across 1,000 miles near Puget Sound. When the calf first died, a resident of San Juan Island spotted six other female orcas mourning with the mother. "As the light dimmed, I was able to watch them continue what seemed to be a ritual or ceremony," the resident told the Center for Whale Research. "They stayed directly centered in the moonbeam, even as it moved. The lighting was too dim to see if the baby was still being kept afloat. It was both sad and special to witness this behavior."

Such behavior looks a lot like mourning, but science often tells us there’s an evolutionary or adaptive purpose behind such actions.

Animals, like humans, are social creatures. They form relationships with one another and at some point death brings those relationships to an end. "They're bonded like us," Barbara King, author of “How Animals Grieve,” told Time magazine. "We're all socially attuned, and in many ways our brains are even wired similarly. Why wouldn't animals mourn?"

The evidence is mounting

Brain studies seem to strengthen the case for animal grief. Human mourning is facilitated by the frontal cortex, the nucleus accumbens and the amygdala, and we share that basic anatomy with many other animals. Some researchers think that if animals do grieve, the mechanisms at work may be the evolutionary precursors of our own mourning process.

There’s even some scientific proof that animals may grieve. Primate researcher Anne Engh collected fecal samples from a group of baboons in Botswana after they witnessed a predator kill one of their own. She tested the samples for increased levels of glucocorticoid (GC) stress markers and found that it was elevated for up to a month after the attack. It was highest in the baboons that had close family or social ties to the victim.

But despite such evidence — as well as the personal accounts shared by biologists, zookeepers and pet owners — even advocates of animal-grief theory are wary about drawing any conclusions just yet.

King points out that the crows could be mourning their dead, but they could just as well be investigating the corpse to learn what killed it. While some primates do carry their dead babies for long periods of time, these same animals have also been observed mating, which doesn’t fit with the human idea of grief.

For now, it’s too soon to tell if animals really are mourning or if we’re simply anthropomorphizing and labeling their behavior as grief.

Editor's note: This article has been updated since it was originally published in April 2013.