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Sunday, Nov. 14, 2010
Mind who you call a 'birdbrain'
Big, black and beady-eyed, jungle crows have more upstairs than you might care to imagine
By ROWAN HOOPER
Eiichi Izawa of Keio University in Tokyo calls them "feathered primates." In Japanese folklore they are the origin of the forest demons known as karasu tengu. Scientists classify them as Corvus macrorhynchos.
The rest of us know them as jungle crows.
Few animals are as ubiquitous in modern Japan as the crow — there are an estimated 20,000 to 30,000 in Tokyo alone. In the Japanese psyche they occupy a niche similar to that filled by tengu demons in feudal times, shifting between being hated and vilified pests and fascinating, resourceful and intelligent animals.
Few people understand this better than Shoei Sugita of Utsunomiya University in Tochigi Prefecture. Sugita has spent his career studying crow behavior and is so well known, even by the public, that he has attracted the nickname "Karasu Hakase" — meaning, "Professor Crow."
Crows tend to come to media attention for their widespread ransacking of garbage bags left in the street for collection or when they attack humans, which sometimes happens in their breeding season between April and May. With a wingspan of over a meter, the animals are certainly fearsome-looking, and will aggressively defend their territory from other birds or anything perceived as a threat.
However, there are also sometimes news reports when discoveries about crow intelligence reveal surprises, such as when it was found that they are smart enough to fashion tools — a behavior once thought to be restricted to apes, and before that something thought unique to humans.
Biologists in New Zealand also reported a few years ago that crows could not only use a long stick to extract a food treat from a box, but if the long stick was out of their reach, they could use a smaller stick to first reach the long one. This is an example of "meta-tool" use — using a tool to manipulate another tool.
In addition, the birds have been documented making a hook from a straight piece of wire in order to retrieve food.
In his latest research, Sugita and his colleagues have now shown that jungle crows can recognize human faces, and can categorize them according to male and female. By testing the birds with different stimuli, the biologists showed that crows use color and facial contours as the basis for differentiating.
Sugita's paper, published in the journal Behavior Processes (DOI reference: 10.1016/j.beproc.2010.10.002), reminds me of reports that crows discriminate between the people they attack. Some women have reported that crows seem to recognize them, and dive-bomb them as they approach garbage bins.
Meanwhile, at Keio University in Tokyo, Eiichi Izawa was involved in creating a 3-D map of the crow brain. While "birdbrain" is a derisory description of someone in English, it turns out it's not justified in the case of crows, whose brains weigh between 10 and 13 grams.
This may not seem much when you think that the bird itself can weigh up to 650 grams, but in the bird world the crow brain accounts for an unusually high proportion of total body weight.
Izawa's atlas of the crow brain shows there is an area called the pallium that corresponds to the part of the brain that we proudly like to think distinguishes mammals: the cortex.
The pallium, which is large and well developed in crows, is where intellectual activity takes place. Thinking, learning and feeling, even, occur there, and it is a key area for integrating information from multiple sources, such as sound and vision.
Crows really do justify their position both in folklore and in the hierarchy of animal intelligence.
Over at the University of Washington, Seattle, researchers showed that a crow will alter its behavior when attempting to steal food from another crow, depending on whether or not the other bird is a relative. The scientists found that the crafty Northwestern crow (Corvus caurinus) uses a passive strategy when it attempts to take food from kin — but becomes aggressive when it tries to steal from an unrelated crow. It's the first time that such a behavior pattern has been observed in any bird species.
Yet crows are undoubted pests. Farmers have the most reason to bemoan these birds, as they eat both seed and mature crops. In 2007, the animals caused an estimated ¥2.6 billion in agricultural losses in Japan; in urban areas, they not only scavenge from garbage bags but can also damage electricity lines and cause power outages.
What's left to be learned about crows?
Like Izawa, Nicky Clayton at Cambridge University in England considers them to be primatelike in the range of behavior and intelligence they show. She told me that rooks — members of the crow family — have been seen picking up discarded cigarette butts and preening their feathers with them. Perhaps the rooks are using the cigarettes as insect repellent.
I mentioned earlier that crows have large brains, but even so, they are only the size of a walnut. So how is it that they are so clever?
Absolute size isn't everything, says Clayton. Look at blue whales, whose brains weigh around 6 kg — compared with the 1.4 kg of a human brain and the relatively miniscule 13 grams of a crow. But blue whales aren't smarter than humans.
What counts is the relative size of the brain. For their body size, the brain size of crows and humans is unusually large, but we don't know why relative brain size and not absolute brain size is the important factor.
Crafty, cunning, perceptive, adaptive; crows can be pests precisely because they are so ingenious. We can try to scare them away, but if there is a resource, crows will figure out a way of getting it. Acknowledging crow intelligence is the best way we have of keeping ahead of them in the urban jungle. Remember that — and next time you see one looking at you, reflect on what's going on in the brain of that "feathered primate."
Follow Rowan Hooper on Twitter at twitter.com/rowhoop. The second volume of Natural Selections columns, translated into Japanese, is published by Shinchosha at ¥1,500. The title is "Hito wa Ima mo Shinka Shiteru (The Evolving Human)."