Questions 20–24 are based on the following passages.
Passage 1 is adapted from Susan Milius, “A Different Kind of Smart.” ©2013 by Science News. Passage 2 is adapted from Bernd Heinrich, Mind of the Raven: Investigations and Adventures with Wolf-Birds. ©2007 by Bernd Heinrich.
In 1894, British psychologist C. Lloyd Morgan published what’s called Morgan’s canon, the principle that suggestions of humanlike mental processes behind an animal’s behavior should be rejected if a simpler explanation will do.
Still, people seem to maintain certain expectations, especially when it comes to birds and mammals. “We somehow want to prove they are as ‘smart’ as people,” zoologist Sara Shettleworth says. We want a bird that masters a vexing problem to be employing human-style insight.
New Caledonian crows face the high end of these expectations, as possibly the second-best toolmakers on the planet.
Their tools are hooked sticks or strips made from spike-edged leaves, and they use them in the wild to winkle grubs out of crevices. Researcher Russell Gray first saw the process on a cold morning in a mountain forest in New Caledonia, an island chain east of Australia. Over the course of days, he and crow researcher Gavin Hunt had gotten wild crows used to finding meat tidbits in holes in a log.Once the birds were checking the log reliably, the researchers placed a spiky tropical pandanus plant beside the log and hid behind a blind.
A crow arrived. It hopped onto the pandanus plant, grabbed the spiked edge of one of the long straplike leaves and began a series of ripping motions. Instead of just tearing away one long strip, the bird ripped and nipped in a sequence to create a slanting stair-step edge on a leaf segment with a narrow point and a wide base. The process took only seconds. Then the bird dipped the narrow end of its leaf strip into a hole in the log, fished up the meat with the leaf-edge spikes, swallowed its prize and flew off.
That was my ‘oh wow’ moment,” Gray says. After the crow had vanished, he picked up the tool the bird had left behind. “I had a go, and I couldn’t do it,” he recalls. Fishing the meat out was tricky. It turned out that Gray was moving the leaf shard too forcefully instead of gently stroking the spines against the treat.
The crow’s deft physical manipulation was what inspired Gray and Auckland colleague Alex Taylor to test other wild crows to see if they employed the seemingly insightful string-pulling solutions that some ravens, kea parrots and other brainiac birds are known to employ. Three of four crows passed that test on the first try.
For one month after they left the nest, I led my four young ravens at least once and sometimes several times a day on thirty-minute walks. During these walks, I wrote down everything in their environment they pecked at. In the first sessions, I tried to be teacher. I touched specific objects—sticks, moss, rocks—and nothing that I touched remained untouched by them. They came to investigate what I had investigated, leading me to assume that young birds are aided in learning to identify food from the parents’ example. They also, however, contacted almost everything else that lay directly in their own paths. They soon became more independent by taking their own routes near mine. Even while walking along on their own, they pulled at leaves, grass stems, flowers, bark, pine needles, seeds, cones, clods of earth, and other objects they encountered. I wrote all this down, converting it to numbers. After they were thoroughly familiar with the background objects in these woods and started to ignore them, I seeded the path we would later walk together with objects they had never before encountered. Some of these were conspicuous food items: raspberries, dead meal worm beetles, and cooked corn kernels. Others were conspicuous and inedible: pebbles, glass chips, red winterberries. Still others were such highly cryptic foods as encased caddisfly larvae and moth cocoons. The results were dramatic.
The four young birds on our daily walks contacted all new objects preferentially. They picked them out at a rate of up to tens of thousands of times greater than background or previously contacted objects. The main initial criterion for pecking or picking anything up was its novelty. In subsequent trials, when the previously novel items were edible, they became preferred and the inedible objects became “background” items, just like the leaves, grass, and pebbles, even if they were highly conspicuous. These experiments showed that ravens’ curiosity ensures exposure to all or almost all items in the environment.
Select an Answer
One difference between the experiments described in the two passages is that unlike the researchers discussed in Passage 1, the author of Passage 2
presented the birds with a problem to solve.
intentionally made the birds aware of his presence.
consciously manipulated the birds’ surroundings.
tested the birds’ tool-using abilities.
Choice B is the best answer. The researchers described in Passage 1 “hid behind a blind” (Passage 1, line 13) to avoid being seen by the crow. The author of Passage 2, on the other hand, made no attempt to conceal his presence; in fact, as he describes it, he “led” the ravens in his study on “walks” (Passage 2, lines 25–26), during which he “touched specific objects” (Passage 2, line 27) and then watched to see whether the birds touched the same objects. The author of Passage 2 notes that the ravens “soon became more independent” (Passage 2, line 30), going their own way rather than continuing to follow the author. From this it is clear that the author of Passage 2, unlike the researchers described in Passage 1, intentionally made the birds aware of his presence.
Choice A is not the best answer because while a case could be made that the author of Passage 2 gave the ravens a problem to solve (Which new objects are best to touch?), the researchers described in Passage 1 presented the crows with a problem as well: how to extract meat from a log. Thus, presenting birds with a problem to solve was not a difference between the experiments.
Choice C is not the best answer because both the researchers described in Passage 1 and the author of Passage 2 consciously manipulated the birds’ surroundings. The crow researchers placed meat pieces in a log and a pandanus plant behind the log (see Passage 1, lines 11–13). The author of Passage 2 put unfamiliar objects on a path for the ravens to find (see Passage 2, lines 33–34). Thus, conscious manipulation of the birds’ surroundings was not a difference between the experiments.
Choice D is not the best answer because there is no evidence that the author of Passage 2 tested the ravens’ tool-using abilities. The passage instead indicates that the author recorded observations about the birds’ interactions with objects naturally occurring in and artificially introduced into the environment.
Students must synthesize information and ideas from paired texts.