Image Source: I09.
Animals, birds and insects all show strange behaviour when one of their number dies. Researchers debate whether this is an auto-reponse based on their sensitivity to chemicals produced by creatures' bodies after death; or whether this behaviour, in the case of some highly intelligent species, indicates a level of rudimentary consciousness. I09 complements my earlier post, "Do Animals Sense Death?" with a report on recent research that Scrub Jays gather together they lose a member of their flock:
The BBC observes that whole disciplines of research are devoted to whether animals and birds display comprehension or distress when one of their number dies. Of course, awareness of death has long commonly been considered to be the hallmark of human consciousness. The language of death is the language (we think) of our knowledge of our own souls.Researchers at UC Davis have observed this funereal behavior in western scrub jays. When one bird spots a dead jay on the ground, it stops what it was doing and starts sending out loud alarm calls. The calls bring in jays from all over, who gather around the body and continue sending out the alarm calls so that as many jays as possible show up near the dead body.
Of course, it's unlikely that these alarm calls are the western scrub jay equivalent of a eulogy. Instead, the researchers are pretty sure that the dead body functions as a warning that predators are nearby, and the jays treat this information seriously enough to gather their entire population around the site of the death. The sight of death had a profound enough effect on the jays that they stopped foraging for the rest of the day, although exactly why this behavior change occurred is difficult to say. It's tempting to say they were too grief-stricken to eat, but we simply don't have enough information to make that assumption.
To better understand what drove the reactions of the jays to the dead bird, the UC Davis researchers presented them with various objects, including recently dead jays, stuffed jays, colored pieces of woods, and stuffed great horn owls (their main predator). A BBC news story charts the birds' reactions:
When the birds were fooled into thinking a predator had arrived, by being exposed to a mounted owl, they also gathered together and made a series of alarm calls. They also swooped down at the supposed predator, to scare it off. But the jays never swooped at the body of a dead bird. The birds also occasionally mobbed the stuffed jays; a behaviour they are known to do in the wild when they attack competitors or sick birds. The fact that the jays didn't react to the wooden objects shows that it is not the novelty of a dead bird appearing that triggers the reaction. The results show that "without witnessing the struggle and manner of death", the researchers write, the jays see the presence of a dead bird as information to be publicly shared, just as they do the presence of a predator.
That same BBC report noted that a mother giraffe exhibited distress and quite unusually lingered around the body of her dead calf, although she did not display this mourning behaviour as long as African elephants do. Similar behaviour has previously - albeit rarely - been reported among giraffes, where a mother stood guard over her dead calf, and the tower also circled the body of the dead baby. One researcher pegs varying responses to death among giraffes along a 'gradient of loss.'
Gauging an emotion like grief, and measuring displays that seem to suggest a non-human comprehension of death and loss of a loved one, is an extremely difficult thing to do. Where and how does the researcher separate genuine consciousness from anthropomorphization?
It is possible that animals, birds and insects all respond to a 'stench of death,' a combination of fatty acids exuded upon death. A death recognition system based on this scent likely evolved 400 million years ago; it helps many species avoid a dead fellow creature, thereby effectively dodging predators and preventing the spread of disease:
E. O. Wilson (born 1929) is the world's leading specialist on ants. You can read more on his research on ants and necrophoric behaviour here and here.When animals die, their corpses exude a particular "stench of death" which repels their living relatives, scientists have discovered.
Corpses of animals as distantly related as insects and crustaceans all produce the same stench, caused by a blend of simple fatty acids. The smell helps living animals avoid others that have succumbed to disease or places where predators lurk. This "death recognition system" likely evolved over 400 million years ago. The discovery was made by a team of researchers based at McMaster University, near Hamilton, Ontario, Canada, and is published in the journal Evolutionary Biology.
Led by Professor David Rollo, the team stumbled upon the phenomenon while studying live cockroaches. "We were examining the aggregation behaviour of cockroaches," says Prof Rollo.
When a cockroach finds a good place to shelter, it gives off pheromones that attract more of its kind. In a bid to identify the exact chemicals involved, Prof Rollo's team extracted body juices from dead cockroaches to see what effect they had.
Take out the dead
"We were astonished to find that nearly 100% of cockroaches avoid shelters treated with whole body extracts. Something in the extract was overriding any attractive chemicals," says Prof Rollo.
"We initiated extensive work to figure out what could be so important to make all these insects go away."
After eliminating a host of other possibilities, such as cockroaches producing alarm signals, they considered the idea that a specific chemical is released by the insects upon death.
"A search of the literature turned up a very old article by famous sociologist and ecologist E. O. Wilson," says Prof Rollo.
By smelling their dead, cockroaches may be able to avoid predators
"Wilson found that ants removed the dead from their nest and dumped them in a cemetery. Moreover, he identified the active signal as oleic acid."
"The famous story goes that Wilson found that a drop of oleic acid on a perfectly healthy ant resulted in her being carried kicking and screaming to the cemetery."