OG剑桥雅思官方指南Test8Section4听力原文与答案 New Caledonian crows and the use of tools
OG Test8 Section4听力原文
I’m going to talk today about research into a particular species of bird, the New Caledonian crow, whose natural habitat is small islands in the Pacific Ocean. And it seems that these Crows are exceptionally resourceful.
Using sticks or other tools to find food isn’t unknown among birds and animals. Some chimpanzees, for example, are known to bang nuts on stones, in order to break the shell and get at the edible kernel inside. One New Caledonian crow, called Betty, bent some straight wire into a hook (Q31) and used it to lift a small bucket of her favourite food from a vertical pipe. This experiment was the first time she’d been presented with wire, which makes it very impressive. Another crow, called Barney, has demonstrated his skill at using sticks to forage for food.
In one research project, scientists from New Zealand and Oxford set captive New Caledonian crows a three-stage problem: if they wanted to extract food from a hole, the crows first had to pullup a string (Q32) to get a short stick, then use that short stick to remove a long stick from a toolbox, and finally use the long stick to reach the food. Amazingly, they worked out how to do this successfully.
Further experiments carried out at Oxford suggest that crows can also use sticks as tools to inspect all sorts of objects, possibly to assess whether or not they present a danger (Q33). The idea for the experiment came from observing the birds using tools to pick at random objects, such as a picture of a spider that was printed on some cloth. In this research, five pairs of crows – including Barney – underwent tests to see how they would react to a variety of objects, which were carefully chosen so the birds wouldn’t be tempted to view them as a possible source of food. As a further precaution, all the crows had been fed beforehand.
On eight occasions, a bird’s first contact was by using a tool. In all three trials, Barney began by using a stick for inspection. One involved a rubber (Q34) snake. First he approached it, but didn’t touch it, then retreated to pick up a stick. He then prodded it with the stick. After some more investigation, he discarded the stick and carried on pecking at the snake more confidently – apparently convinced that it wouldn’t move.
In other experiments, two different birds, called Pierre and Corbeau, also made a first approach with tools on three separate occasions. Pierre used a short piece of woodchip to touch a light (Q35) which was flashing, and Corbeau was seen prodding a metal toad with a stick.
Significantly, the crows tended to use the sticks only to make their first contact with the object. Subsequently, they either ignored the object or dropped the tool and pecked at the object – which is very different from using the tool to get access to food.
So what conclusions can be drawn from the research? Evidence is building up from experiments such as these that the birds are able to plan their actions in advance, which is very interesting for understanding their cognition. They don’t seem to be responding in a pre-programmed sort of way: it may even be possible that they’re able to view a problem and work out what the answer is. However, this article is from Laokaoya website, a major difficulty is assessing whether this tool-using behaviour is a sign of intelligence (Q36). To some extent, this is related to the ecological circumstances in which the animal is found.
So scientists want to find out much more about how the crows behave in their native habitat, and a team from Exeter and Oxford universities is carrying out research in New Caledonia. They’re looking into whether the birds’ way of searching for food gives them any possible evolutionary advantage. The birds are hard to observe, as they live in a region of mountainous forest, so the researchers have attached tiny cameras to the tails (Q37) of some birds, as one method of investigating their behaviour.
The birds are masters at using sticks to find their food, in particular beetle larvae from the trees. It’s possible that the birds can derive so much energy (Q38) from these grubs that they only need to eat a few each day. This would mean that they wouldn’t have to spend most of their waking time searching for food, as most animals do.
The beetle larvae have a distinct chemical (Q39) make-up, which can be traced through the feathers and blood of birds that eat them. Scientists have collected samples from crows in order to estimate the proportion of larvae in their diet (Q40). They should then be able to gauge the extent to which individual birds depend on using sticks to feed themselves.
We’ve learnt a great deal about the ability of New Caledonian crows to use tools, and some very interesting research is being carried out into them.
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