题型:阅读理解 题类:常考题 难易度:普通
山东省威海市威海文登区2021届高三上学期英语期中试卷(含完整音频)
We all know that cuckoos (杜鹃) use a mean way to raise their babies. The female cuckoos lay their eggs into other parents' nests. If the cuckoo chick hatches earlier than other eggs, it will push other eggs onto its back, one by one, and make the eggs fall out.
"It's amazing," notes Daniela Canestrari. She's a biologist who studies animal behavior at the University of Oviedo in Spain. At first, she wasn't focusing on brood parasitism. She just wanted to learn about crow behavior. But some crow nests had been parasitized by spotted cuckoos. When the cuckoo eggs hatched, the chicks didn't push crow eggs out of the nest. They grew up alongside crow chicks.
"At a certain point, we noticed something that really puzzled us," Canestrari says. Nests containing a cuckoo chick seemed more likely to succeed. By that she means that at least one crow chick survived long enough to fly out on its own.
The researchers wondered if the reason had something to do with attackers. Wild cats sometimes attack crow nests, killing all the chicks. Are the cuckoos helpful in defending nests?
So the scientists found crow nests containing a cuckoo chick. Meanwhile, they moved some cuckoos to crow nests that weren't parasitized. Then the researchers monitored whether the nests succeeded. They also watched nests that had never contained a cuckoo chick.
About 70 percent of crow nests with added cuckoo chicks succeeded. This rate was similar to that of chicks in parasitized nests that kept their cuckoos. But among nests whose cuckoo chicks were removed, only about 30 percent succeeded. And this rate was similar to what was seen in nests that never held a cuckoo.
"The presence of the cuckoo was causing this difference," Canestrari concluded. Then how did the cuckoos slim down the attackers and protect the crow nests? The researchers found cuckoos produced smelly liquid when they were in danger. The results showed that the attackers all turned up their noses when they were exposed to the liquid-coated meat.
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