Ravens Know if They're Being Spied On
The finding suggests the birds are able to understand what might be going on in the mind of another individual.
Ravens can imagine being spied upon by a hidden competitor, showing a capacity for abstraction once thought to be exclusively human, according to a study released Tuesday.
In a clever set of experiments, scientists showed that the famously intelligent birds take extra care to hide food if they suspect their movements are being monitored by another raven, even when the second bird is not really there.
The findings, published in the journal Nature Communications, suggest that ravens - without recourse to direct observation - are able to understand what might be going on in the mind of another individual.
"This shows that traits that we consider ‘uniquely human' may be found in animals too," said lead author Thomas Bugnyar, a professor at the University of Vienna and a leading expert on social cognition in animals.
Over a six-month period scientists studied 10 ravens that had been raised in captivity.
The birds were placed in adjoining rooms divided by a window, that was initially left uncovered so one raven could watch while the other was given food to hide.
Researchers then covered the window, but left a peephole in it that the birds were taught they could see and be seen through.
Once this basic training was in place, the scientists played a recording of raven sounds while a bird was in the process of storing its food.
Only when the peephole was open, however, did the raven take extra care to hide its goodies. If the peephole remained closed, the bird - even when raven noises were audible - somehow concluded that it could not be spied upon.
Previous research, mainly with chimpanzees, has shown that non-human animals can understand what others are seeing.
But it was assumed that they did so by monitoring an individual's head or eye movements, what scientists call "gaze cues."
"It was still an open question whether any non-human animal can attribute the concept of ‘seeing' without relying on behavioural cues," the study noted.
Even without those cues, however, the ravens showed that they understood they were perhaps being watched, and changed their behaviour accordingly.
"This strongly suggests that ravens make generalisations based on their experience, and do not merely interpret and respond to behavioural cues from other birds," said Bugnyar.
Scientists determined that the caching bird thought it was being observed when it hurried to hide its food, or when it later - once the coast was clear - returned to improve the food's hiding place.
Young ravens are known to form and break alliances, demonstrating "social flexibility." As adults, they typically defend territory and live in long-term monogamous relationships.
Some animals are safeguarded against stomach upset, finds new research that shows not all species suffer from problems like indigestion as we do. In fact, these species eat some of the world's most unpalatable edibles, such as poop, vomit and road kill. Turkey vultures "seem to have a natural physical defense against letting things through their system," Lars Hansen, a professor in the Department of Environmental Science at Aarhus University, told Discovery News. Hansen is the co-author of a new paper on vultures that is published in the latest issue of Nature Communications. The researchers are also studying other animals with incredibly tough digestive systems. At least three major things allow turkey vultures to eat food, such as rotting road kill, which other animals would pass up. The first is that conditions in their stomachs are highly acidic, to the point that, as Hansen said, "even the DNA of prey animals disappeared on passage through the digestive system." Turkey vultures also have a "probiotic garden" that either wards off pathogens or occupies the biochemical niche for them, thus preventing bad compounds from taking hold. These vultures also have strong immune systems that help to ward off health dangers, like botulism toxins.
To survive in harsh food-poor environments, polar bears feast on almost anything meaty. Like turkey vultures, they have special bacteria in their gut that is actually related to harmful bacteria, helping to ward off digestion problems.
Lions are facultative scavengers, explained Michael Roggenbuck, co-author of the paper. This means that lions kill prey as well as scavenge carcasses from already dead animals. It's not hard to imagine that our ancient human ancestors may have done the same, not wanting to refuse meat for the taking.
Crows are not know for food choosiness. Roggenbuck explained they are obligate scavengers -- animals that mainly consume the decaying flesh of dead animals (carrion). "It is very interesting that the majority of obligate scavengers are birds," he said. "One hypothesis is that this is due to the fact that birds can reach larger areas with an increase in available carcasses, compared to the terrestrial predators that are locally limited."
Beetles, and especially dung beetles, are also obligate scavengers. There is little doubt that a creature existing on excrement has a proverbial iron gut. Turkey vultures were also seen pulling flesh from the nether regions of dead prey, ingesting waste material along with everything else. Dogs can do the same. Roggenbuck said that canines are facultative scavengers. As such, they receive an honorable mention on this list.
While sleek, leopards also resort to scavenging carcasses. Because of this repeated behavior, they too have evolved digestive tracts that can tolerate meat that would sicken and repulse humans. Hansen said, "I think that the fact that most animals don't touch the carcasses makes them an attractive food source that can be harvested without having to spend energy fighting against many others."
Jackals fall into the same category as dogs, as facultative scavengers. While jackals might choose a fresh kill over old flesh for dinner, they still go after the latter and don't seem to be bothered by it.
Ravens and other consumers of carrion are like nature's cleanup crew. By eating things that others cannot tolerate, they help to clean their environments, thereby helping to protect others within the ecosystem. Many studies have shown how ravens are highly intelligent. Their choice of meals, however unappetizing to us, is strategic, with many such birds growing in numbers in suburban and urban areas now.
Syenas are on the long list of facultative scavengers, Roggenbuck said. Hyenas have ultra tough guts to handle eating nearly anything edible that comes in their path. Coyotes fall into this category too.
Hansen and his team have literally have pulled brown rats, which also have the unfortunate name "sewer rats," out of city sewers in order to examine the microbial communities living in the scrappy rats' guts. Such rats somehow tolerate incredible filth. By gaining a better understanding of animals' cast iron stomachs researchers hope to find new treatments for colon and stomach cancers in humans, as well as other diseases and illnesses affecting our digestive tract.