科学美国人60秒--鸟类实际上是如何飞行的

Answering an Age-Old Mystery: How Do Birds Actually Fly?

Equally surprising is the fact that we still do not know how birds actually stay airborne.

 

This is Scientific American’s  60-Second Science, I'm Emily Schwing.

Have you ever looked up to see a  hawk¹ soar overhead, or a small chickadee flit by and wondered: How do they do that?

Believe it or not, scientists never really knew either?—until now. 

Talia Lowi-Merri: I looked at the relationship between form and function in the most basic sense.

Talia Lowi-Merri is a Ph.D. student at the University of Toronto in Canada. She says bird flight has everything to do with the shape and size of a bird’s sternum, or breastbone. Bird sternums have a projection² from the middle called the keel, and this is where the flight muscles are attached. 

Lowi-Merri: It's plausible³ to think that this element is important for flight. But why does it vary so much in shape and size relative to the body? There are all these questions about it that haven't been answered in the past.

So, Merri set out to find some answers using a database of CT scanned sternums from 105 different bird species, like the Red-capped lark⁴, Leach’s Storm petrel and the Southern cassowary. She also included two extinct birds: the Dodo and the Great auk. The scans combine a series of x-rays to create three dimensional images.

Lowi-Merri: There have been newer technologies come out recently to look at shape in three dimensions. And so because the sternum is a complex element in three dimensions, it's not just a 2-D bone, it's got projections⁵ about the middle and its sides. Looking at it in three dimensions is the best way to quantify the shape and analyze⁶ it in a statistical⁷ framework. So more recently, those methods have become more accessible. And I guess because of that, I was able to do it now and maybe 10 or 15 years ago, it wasn't possible.

Merri and colleagues used the scans to create computerized 3D models. 

Lowi-Merri: And so when you do that, you can move it around. You can place points on it in the important spots. And so that's what I was doing. I was putting these dots that are called landmarks⁸, and the landmarks basically quantify in 3-D computer space where the important points are on the element.

The findings, published in BMC Biology, show that sternum size and shape has a direct impact on the way a bird flies. [Talia M. Lowi-Merri et al., The relationship between sternum variation and mode of locomotion⁹ in birds]

[Sound of an eagle]

Lowi-Merri: So an eagle would be soaring and wouldn't be moving its wings as much. It just has its arms stretched out, and it has very intricate structures in its wings and at its shoulder to hold the wings out, but it doesn't have to use as much flapping power.

But compare the majestic¹⁰ eagle with a frantically¹¹ flapping duck…

[Sound of ducks flying]

Birds with a deep sternal keel fly more slowly, those with long sternums are associated with running birds. Merri also looked at foot-propelled, underwater diving birds. These are species like the cormorant¹², the loon¹³ and the grebe. 

Lowi-Merri: They have this streamlined sternum with lower sternal keels. Everything is kind of compact and flattened¹⁴, but you actually see something really similar in birds that are wing propelled divers¹⁵.

Those wing-propelled divers include small birds you might find on the ocean - puffins, common murres and penguins¹⁶. Merri says whether wing or foot-propelled, the sternums of these birds are similar in shape. 

All other sorts of factors are possibly most likely contributing to the shape of the sternum, not just locomotion, things like birds that dance to attract a mate or how big their egg is relative to their body size. We've just scratched the surface, looked at one aspect of variation, but there's so much more.” (00:33)

Merri believes that the shape and structure of the sternum impacts how different species of birds breathe. She also says different methods of flight mean different resource demands for individual species. 

Diving deep into how birds fly today can tell scientists a lot about how they evolved over millions of years.

Lowi-Merri: So, birds evolved from dinosaurs¹⁷… and we don't know exactly which fossil birds and which dinosaurs were capable of flight. But, gaining a better understanding of how birds fly today is the key to completing that picture of how the dinosaurs were moving through the world.

Merri plans to dig into fossil birds next, in part to learn more about the origins of flight.

Lowi-Merri: The thing about fossil birds is that a lot of them are flattened into rock slabs¹⁸. But there are so many amazing bird fossils, especially from China …. And so they will have to be studied a little bit differently because they may not be able to put them in a three dimensional context, as they did with the modern bird sterna.

For now, though, Merri says she’s looking differently at the small, passerine birds that flit by her windows and dominate the tree branches in her backyard in Ontario. 

Lowi-Merri: They're mostly continuous flapping birds. They're flapping pretty quickly. They're moving from branch to branch. They're trying to keep away from predators¹⁹ and get some food, whether it's insects or berries. it made me think about how their skeletons are structured and also how their muscles are working much differently than, let's say, a hawk that's soaring above. And so they would require different metabolism²⁰ and different food sources and how they use that in their body would be very different.

[Bird wing flapping]

For 60-Second Science, I’m Emily Schwing.

1 hawk   

n.鹰，骗子；鹰派成员

参考例句：

• The hawk swooped down on the rabbit and killed it.鹰猛地朝兔子扑下来,并把它杀死。
• The hawk snatched the chicken and flew away.老鹰叼了小鸡就飞走了。

2 projection   

n.发射，计划，突出部分

参考例句：

• Projection takes place with a minimum of awareness or conscious control.投射在最少的知觉或意识控制下发生。
• The projection of increases in number of house-holds is correct.对户数增加的推算是正确的。

3 plausible   

adj.似真实的，似乎有理的，似乎可信的

参考例句：

• His story sounded plausible.他说的那番话似乎是真实的。
• Her story sounded perfectly plausible.她的说辞听起来言之有理。

4 lark   

n.云雀，百灵鸟；n.嬉戏，玩笑；vi.嬉戏

参考例句：

• He thinks it cruel to confine a lark in a cage.他认为把云雀关在笼子里太残忍了。
• She lived in the village with her grandparents as cheerful as a lark.她同祖父母一起住在乡间非常快活。

5 projections   

预测( projection的名词复数 )； 投影； 投掷； 突起物

参考例句：

• Their sales projections are a total thumbsuck. 他们的销售量预测纯属估计。
• The council has revised its projections of funding requirements upwards. 地方议会调高了对资金需求的预测。

6 analyze   

vt.分析，解析 (=analyse)

参考例句：

• We should analyze the cause and effect of this event.我们应该分析这场事变的因果。
• The teacher tried to analyze the cause of our failure.老师设法分析我们失败的原因。

7 statistical   

adj.统计的，统计学的

参考例句：

• He showed the price fluctuations in a statistical table.他用统计表显示价格的波动。
• They're making detailed statistical analysis.他们正在做具体的统计分析。

8 landmarks   

n.陆标( landmark的名词复数 )；目标；（标志重要阶段的）里程碑 ~ (in sth)；有历史意义的建筑物（或遗址）

参考例句：

• The book stands out as one of the notable landmarks in the progress of modern science. 这部著作是现代科学发展史上著名的里程碑之一。 来自《现代汉英综合大词典》
• The baby was one of the big landmarks in our relationship. 孩子的出世是我们俩关系中的一个重要转折点。 来自辞典例句

9 locomotion   

n.运动，移动

参考例句：

• By land,air or sea,birds are masters of locomotion.无论是通过陆地，飞越空中还是穿过海洋，鸟应算是运动能手了。
• Food sources also elicit oriented locomotion and recognition behavior patterns in most insects.食物源也引诱大多数昆虫定向迁移和识别行为。

10 majestic   

adj.雄伟的，壮丽的，庄严的，威严的，崇高的

参考例句：

• In the distance rose the majestic Alps.远处耸立着雄伟的阿尔卑斯山。
• He looks majestic in uniform.他穿上军装显得很威风。

11 frantically   

ad.发狂地, 发疯地

参考例句：

• He dashed frantically across the road. 他疯狂地跑过马路。
• She bid frantically for the old chair. 她发狂地喊出高价要买那把古老的椅子。

12 cormorant   

n.鸬鹚，贪婪的人

参考例句：

• The cormorant is a large,long-necked,dark-colored bird which lives near sea coasts and eats fish.鸬鹚是一种长脖子黑颜色的大鸟，生活在海滨而且以吃鱼为生。
• The exciting cormorant fishing performance is over there.那边有令人刺激的鱼鹰捕鱼表演。

13 loon   

n.狂人

参考例句：

• That guy's a real loon.那个人是个真正的疯子。
• Everyone thought he was a loon.每个人都骂他神经。

14 flattened   

[医]（水）平扁的，弄平的

参考例句：

• She flattened her nose and lips against the window. 她把鼻子和嘴唇紧贴着窗户。
• I flattened myself against the wall to let them pass. 我身体紧靠着墙让他们通过。

15 divers   

adj.不同的；种种的

参考例句：

• He chose divers of them,who were asked to accompany him.他选择他们当中的几个人，要他们和他作伴。
• Two divers work together while a standby diver remains on the surface.两名潜水员协同工作，同时有一名候补潜水员留在水面上。

16 penguins   

n.企鹅( penguin的名词复数 )

参考例句：

• Why can penguins live in cold environment? 为什么企鹅能生活在寒冷的环境中？ 来自《简明英汉词典》
• Whales, seals, penguins, and turtles have flippers. 鲸、海豹，企鹅和海龟均有鳍形肢。 来自《现代英汉综合大词典》

17 dinosaurs   

n.恐龙( dinosaur的名词复数 )；守旧落伍的人，过时落后的东西

参考例句：

• The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
• Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》

18 slabs   

n.厚板，平板，厚片( slab的名词复数 )；厚胶片

参考例句：

• The patio was made of stone slabs. 这天井是用石板铺砌而成的。 来自《简明英汉词典》
• The slabs of standing stone point roughly toward the invisible notch. 这些矗立的石块，大致指向那个看不见的缺口。 来自辞典例句

19 predators   

n.食肉动物( predator的名词复数 )；奴役他人者（尤指在财务或性关系方面）

参考例句：

• birds and their earthbound predators 鸟和地面上捕食它们的动物
• The eyes of predators are highly sensitive to the slightest movement. 捕食性动物的眼睛能感觉到最细小的动静。 来自《简明英汉词典》

20 metabolism   

n.新陈代谢

参考例句：

• After years of dieting,Carol's metabolism was completely out of whack.经过数年的节食，卡罗尔的新陈代谢完全紊乱了。
• All living matter undergoes a process of metabolism.生物都有新陈代谢。