칼레도니아 까마귀는 가느다란 나무가지로 고리(Hook)를 만들어 고목의 구멍에 꽃아 먹이찾는 지능이 발달한 새.
동물의 세계를 좀 주의깊에 들여다 보면, 그들도 인간 이상으로 머리가 발달돼 있다는것을 보게된다. 오늘은 북미 대륙에서 서식하고 있는 Caledonian 까마귀의 생존을 위한 그들만의 삶의 본능으로 먹이를 찾아내는 진기한 방법을 볼수 있었다. 동영상을 보면 참 신기해 보였다.
아래에 그내용들을 들여다 보았다.
까마귀는 가느다란 나무가지를 꺽어, 나무가지의 끝을 마치 낚시(Hook)처럼기술적으로 구부려서, 통나무에 나있는 구멍에 집어넣는 새로 명성이 알려져 있는데, 그렇게 하면서 구멍속에 숨어있는 유충이나 곤충들을 밖으로 끄집어내 먹이로 이용하는데, 이러한 행동의 목적이 지금까지 알려지지 않아 여러가지 추측만 낳게 했었다.
우리가 백에 들어있는 칩을 빨리꺼내먹기위해 백을 열려고 잠시 고민하다가 가위를 찾아서 백윗부분을 자르고 스낵칩을 쉬게 꺼내 먹을수 있었던 경험이 있을 것이다. 이까마귀는 끝이 꼬부려진 가느다란 나뭇가지를 이용하여 구멍에 넣고 마치 낚시를 하듯이 후벼서 그속의 유충이나 곤충을, 그냥 보통의 나뭇가지를 넣어 곤충을 꺼내 먹는것보다, 약 10배 이상 빠르게 해결할수 있다 라고, Nature Evolution and Ecology에서 새로 연구한 결과를 발표한 것이다.
과학자들은 New Caledonian 까마귀들이 이런 모양의 나뭇가지 Hook을 기술적으로 만들어 이용한다는것은 까마귀가 진화하고 있다는 근거를 수립하였는데, 이렇게 인간이 아닌 동물인, New Caledonian까마귀가 먹이를 찾기위해 Hook을 만들어 이용한다는것은 새롭게 알려진 유일한 케이스이다.
연구학자들은 까마귀 17마리 붙잡아 넓은 야생에 만들어 놓은 커다란 새장에서 관리해 보았다. 몇마리의 까마귀에게는 그들이 좋아하는 어린나뭇가지를 이용하여만든 훅을 사용, 쉽게 꺼내먹을수 있도록 했고, 다른 까마귀들은 연구자들이 야생숲에서 채취한 반듯한 나뭇가지를 사용토록했었다.
즉 우리 인간사회에서 처럼 그들도 먹이감을 쉽게 찾아서 생명을 유지할수있기위한 수단으로 도구를 만들어 사용하고 있다는 뜻이다.
A New Caledonian crow holds a hooked stick in its beak. (James St. Clair)
"If you have a tool that is 10 times more efficient, it will considerably raise your survival prospects — there's more food to raise your offspring," said Christian Rutz, a behavioral ecologist at the University of St. Andrews in Scotland who led the project. "It just pays off."
On New Caledonia, a forest-covered island east of Australia, the jet-black crows pick out sticks to help them hunt for winkle beetle grubs and insects. Some of the crows take an extra step.
Researchers have observed the birds as they select a forked stem from a particular local shrub. Then the crows trim the side stems and carefully carve and peel the end until it forms a "neat little hook," Rutz said.
The birds must think their creations are neat, too — they often carry, store and re-use their tools.
Rutz and his colleagues wanted to know why these birds go the extra mile to perform such a complex behaviour.
So they captured 17 wild crows and temporarily housed them in field aviaries. Some of the birds were allowed to fashion their hooked tools from the local shrub that's a favorite material for tool-making. Others were provided nonforked twigs and stalks that researchers collected from the forest.
Both groups of crows were timed as they tried to fish out spiders and pieces of meat placed in holes drilled in a log. Depending on the task, the crows armed with hooks retrieved the bait three to 13 times faster than the crows that stuck with straight sticks.
But this isn't just a study about crafty crows, Rutz said. "It's about why, in very few cases, technology advances."
The oldest known fishing hooks are only about 23,000 years old. About 1,000 generations later, we now have smartphones, supercomputers and an International Space Station. In evolutionary terms, that's a blink of an eye, Rutz said.
Animals that use tools typically use only one type of tool. Chimpanzees employ stones for a variety of tasks, sea otters bang open shells with rocks and Galapagos woodpecker finches use twigs to hunt.
But aside from humans, the New Caledonian crow is the only known species that looks at its primitive tool and thinks, "I can improve this."
New Caledonian crows are the only nonhuman animal known to manufacture tools. (James St. Clair)
"Normally nonhuman tools, they stay what they are," Rutz said. "Now with these crows, we have experimentally shown that their technology advances."
The researchers are eager to find out how the birds gain their tool-making knowledge. Is the ability "hard-wired" in their genes? Do crow chicks learn it by watching their parents or other adults?
Finding the answers won't be easy.
For starters, New Caledonian crows tend to use their tools high up in the trees, making their behavior difficult to observe in the wild. And when Rutz tried to observe them in captivity, the birds didn't sculpt their sticks into hooks.
One way to get to the bottom of question would be to perform a "cross-fostering" experiment. In such a study, chicks from a family of hooked tool-making crows would be exchanged with a nest of more simple tool users. But this isn't an option on New Caledonia, Rutz said.
Depending on the area of the island, different populations of crows will make various types of tools using materials they have available. "It looks like there are local adaptions, there are possibly local cultures," Rutz said. "And that is absolutely fascinating."
Cross-fostering chicks from different areas "has the potential to really irreversibly alter the system we hope to study," he said.
A tagged New Caledonian crow holds a hooked stick in its mouth. (James St. Clair)
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