Anyone who has watched crows, jays, ravens and other members of the corvid family will know they're anything but "birdbrained."
For instance, jays will sit on ant nests, allowing the angry insects to douse them with formic acid, a natural pesticide which helps rid the birds of parasites. Urban-living carrion crows have learned to use road traffic for cracking tough nuts. They do this at traffic light crossings, waiting patiently with human pedestrians for a red light before retrieving their prize.
Yet corvids may be even cleverer than we think. A new study suggests their cognitive abilities are a match for primates such as chimpanzees and gorillas. Furthermore, crows may provide clues to understanding human intelligence.
Published tomorrow in the journal Science, the study is co-authored by Nathan Emery and Nicola Clayton, from the departments of animal behavior and experimental psychology at Cambridge University, England.
They say that, while having very different brain structures, both crows and primates use a combination of mental tools, including imagination and the anticipation of possible future events, to solve similar problems. They base their argument on existing studies.
Emery and Clayton write, "These studies have found that some corvids are not only superior in intelligence to birds of other avian species (perhaps with the exception of some parrots), but also rival many nonhuman primates."
Increasingly, scientists agree that it isn't physical need that makes animal smart, but social necessity. Group living tends to be a complicated business, so for individuals to prosper they need to understand exactly what's going on. So highly social creatures like dolphins, chimps, and humans tend to be large-brained and intelligent.
The study notes that crows are also social and have unusually large brains for their size. "It is relatively the same size as the chimpanzee brain," the authors said.
They say that crows and apes both think about their social and physical surroundings in complex ways, using tool use as an example.
Like apes, many birds employ tools to gather food, but it isn't clear whether chimps or crows appreciate how these tools work. It may be that they simply discover their usefulness by accident. However, studies of New Caledonian crows, from the South Pacific, suggest otherwise.
New Caledonian crows manufacture two very different types of tool for finding prey. Hooks crafted from twigs are used to poke grubs from holes in trees, while they also cut up stiff leaves with their beaks, carefully sculpting them into sharp instruments for probing leaf detritus for insects and other invertebrates.
A New Caledonian crow in captivity learned how to bend a piece of straight wire into a hook to probe for food.
Such sophisticated tool manufacture and use is unique in non-human wild animals, according to Jackie Chappell, a UK-based zoologist who has studied the birds.
Emery and Clayton compare the crow's handiwork to minor human technological innovations. And because different New Caledonian crow populations make these tools to slightly different designs, some scientists take this as evidence of some form of culture, as has been suggested in chimpanzees.
Other corvids may use memories of past experiences to plan ahead.
In the case of Western scrub jays, a previous study by Emery and Clayton suggests jays with past experience of pilfering food caches collected by other jays can then use this knowledge to protect their own caches.
Lab experiments showed that if a habitual thief was observed while burying its own cache, it would later go back and move it when no other bird was looking. Meanwhile, "innocent" jays did not exhibit the same cunning.
The researchers also argue that such behavior suggests Western scrub jays are able to second guess another's intentions, or, to put it another way, get into another bird's mind. In which case, this could be evidence for imagination.
Emery and Clayton write, "Western scrub jays may present a case for imagination because the jays needed to have remembered the previous relevant social context, used their own experience of having been a thief to predict the behavior of a pilferer, and determined the safest course of action to protect the caches from pilferage."
Studies to assess similar cognitive abilities in apes have been inconclusive, according to John Pearce, professor of psychology at Cardiff University in Wales.
"[The Western scrub jay study] is some of the best evidence going that one animal can understand what another is thinking," he added.
Pearce believes we can gain insights into the basic mechanisms of human intelligence through the study of animals. He says language is generally considered to be one of the major divisions between human and animal intelligence, which makes Western scrub jays especially noteworthy.
He said, "What's so interesting is that while Western scrub jays may not have language, the research shows they've got many of the intellectual abilities that humans have. This suggests that many of our intellectual abilities which we think we need language for perhaps we don't in fact need language for. That then makes us try to understand these abilities in a different way."
If we're as smart as we think we are, perhaps we need to keep an even closer eye on those clever old crows.