Under the Microscope/Prof William Reville:The derogatory term "bird brain" indicates a person of low intelligence. Presumably the term originates in the observation that the average bird's brain is necessarily very small, since the bird's head is small.
There is another phrase, "valuable goods come in small parcels" which actually applies more aptly to birds' brains because many birds are unusually clever. Ravens are a particular case in point. A fascinating article by Bernd Heinrich and Thomas Bugnyar in Scientific American(April 2007) describes research indicating that ravens can use logic to solve problems and that they can distinguish individuals (both ravens and humans) and attribute knowledge to them.
There are many stories about the clever behaviour of ravens, eg making false food caches to mislead raiders, but these stories don't prove that ravens can reason. Ravens are not the only member of the crow family that demonstrate clever behaviour, but, until now, nobody has been able to divine whether this behaviour represents innate programming, trial and error or reasoning.
To reason means to visualise alternatives in the mind, to evaluate them and to choose the correct one. Heinrich and Bugnyar have carried out careful experiments and the simplest and most obvious explanation of the results is that ravens can think logically.
One test of the ravens devised by Heinrich and Bugnyar was to hang food from a perch by a string to see if the birds could retrieve the food. To get the food the raven has to reach down from the perch, grab the string with its beak, pull up on the string, place the loop of pulled-up string on the perch, step on the string firmly enough to hold it, let go of the string, reach down again to grab the string in the beak, and repeat this sequence six or more times in a row to eventually get the treat.
They found that some mature ravens would size up the situation for several minutes and then successfully complete this multi-step operation in about 30 seconds, without any initial trial and error attempts. These animals had not encountered this problem in the wild and therefore had not already figured it out by trial and error. The simplest explanation is they imagined the possibilities and thought out the steps to take.
Success rate on this task correlated with the maturity of the bird. Birds only one to two months past the fledgling stage were unable to solve this problem. One-year-old birds averaged six minutes to solve the problem, and before getting the solution they tried other options such as flying at the food.
The capacity to test actions in the mind and to project the outcomes of these actions is either lacking or present only to a very small extent in most animals. Heinrich and Bugnyar explain why this makes adaptive sense.
Many animals with tiny brains are genetically pre-programmed to carry out very precise behaviours. Each species of bird is programmed to make its own peculiar design of nest - eg all barn swallows build a shelf-nest from mud that hardens when it dries. This behaviour is not learned, it does not depend on thinking and it is completely reliable. Why is all animal behaviour then, including our own, not hardwired and reliable?
The answer is that prewired responses would be a grave hindrance to any animal evolving in a complex and unpredictable environment. Any animal that can recognise its fellow animals as individuals (as ravens can - shown by other experiments conducted by the authors) is living in a complex social environment where the ability to predict the responses of others is very important. The pressure to develop this ability to predict is often cited as the driving force behind the evolution of intelligence. How did the ravens' social environment press for the selection of intelligence?
Ravens do some hunting but mainly live off the food killed by other animals. These other predator animals could also kill the ravens who must actively learn how to protect themselves in the presence of these carnivores. Different precautions are necessary for different carnivores. A single hardwired response would therefore be inappropriate and very dangerous.
Ravens learn the dangerous characteristics of different predators while they are young. Juvenile birds interact with those predators, usually by landing behind them and nipping them. This is a form of play that is hardwired into the ravens' behaviour. In this way they learn the characteristics of different carnivores, eg the wolf, learn how much they can get away with, the distance they must keep to ensure safety, and so on. The play also accustoms the carnivores to the more or less constant presence of the birds. When a wolf, for example, kills a prey, it feeds quickly on the carcass, which doesn't last long. It therefore makes sense for the ravens to feed on the carcass at the same time. They also remove caches of food from the carcass, which they hide by burial and camouflage with debris. These caches are later retrieved.
Certain other types of crow also display superlative mental capacities. For example, the New Caledonian crow makes tools out of leaves to extract grubs from crevices in wood. In a fascinating demonstration of the cleverness of this bird, Oxford University researchers demonstrated how a captive Caledonian Crow bent a straight piece of wire into a hook to retrieve a piece of meat from a tube. This can be viewed on video at news.nationalgeographic.com/news/2002/08 /0808_020808_crow.html