科学美国人60秒 回答一个古老的谜团-鸟类是如何飞行的（在线收听）

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

回答一个古老的谜团：鸟类是如何飞行的

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

这是《科学美国人》的60秒科学，我是艾米莉·施温。

Have you ever looked up to see a  hawk 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.

你有没有抬头看到一只老鹰在头顶翱翔，或是一只小山雀飞过，你会想：它们是怎么做到的？

信不信由你，科学家们也从未真正知道?—直到现在。

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 projection from the middle called the keel, and this is where the flight muscles are attached.

Lowi-Merri: It's plausible 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.

塔里亚·洛维·梅里：我从最基本的意义上研究了形式和功能之间的关系。

塔里亚Lui-Meiri是加拿大多伦多大学的博士生。她说鸟类的飞行与鸟类胸骨的形状和大小有关。鸟的胸骨中间有一个突起，叫做龙骨，这是飞行肌肉附着的地方。

洛伊·梅里：认为这个元素对飞行很重要是有道理的。但为什么它的形状和大小与身体有如此大的差异呢？所有这些问题在过去都没有得到回答。

So, Merri set out to find some answers using a database of CT scanned sternums from 105 different bird species, like the Red-capped lark, 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.

因此，梅里开始利用CT扫描的105种不同鸟类的胸骨数据库寻找答案，比如红顶云雀、利奇的风暴海燕和南方食火鸡。她还包括两种已灭绝的鸟类：渡渡鸟和大海雀。这些扫描结合了一系列的x射线来创建三维图像。

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 projections about the middle and its sides. Looking at it in three dimensions is the best way to quantify the shape and analyze it in a statistical 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.

Lowi Merri：最近出现了一些新技术，可以从三维角度观察形状。因为胸骨在三维空间是一个复杂的元素，它不仅仅是一块二维的骨头，它的中部和侧面都有投影。从三维角度观察它是量化形状并在统计框架中进行分析的最佳方式。所以最近，这些方法变得更容易使用。我想正因为如此，我现在能够做到，也许在10年或15年前，这是不可能的。

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 landmarks, and the landmarks basically quantify in 3-D computer space where the important points are on the element.

梅里和同事们利用扫描技术创建了计算机化的3D模型。

洛伊·梅里：所以当你这么做的时候，你可以把它移动。你可以在重要的地方放点。这就是我所做的。我把这些点称为地标，地标基本上是在三维计算机空间中量化的，其中重要的点在元素上。

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 locomotion in birds]

这项研究结果发表在《BMC生物学》上，表明胸骨的大小和形状对鸟类的飞行方式有直接影响。

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 majestic eagle with a frantically flapping duck…

洛维·梅里：所以一只老鹰会翱翔，不会像以前那样动翅膀。它只需要伸展手臂，翅膀和肩膀上有非常复杂的结构来支撑翅膀，但它不需要使用太多的拍打力。

但是把雄鹰和疯狂拍打的鸭子相比…

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 cormorant, the loon and the grebe.

胸骨深的鸟飞得更慢，胸骨长的鸟与奔跑的鸟有关。梅里还研究了脚推动的水下潜水鸟类。这些物种包括鸬鹚、龙和灰蝶。

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

Lowi Merri：他们有流线型胸骨和较低的胸骨龙骨。所有的东西都是紧凑而扁平的，但实际上你在鸟类身上看到了一些非常相似的东西，它们是翅膀驱动的潜水员。

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

这些由翅膀推动的潜水员包括你在海洋中可能会发现的小鸟——海雀、普通的墨鱼和企鹅。梅里说，无论是用翅膀还是脚推动，这些鸟的胸骨形状都很相似。

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)

所有其他类型的因素很可能都会影响胸骨的形状，而不仅仅是运动，比如鸟类为了吸引配偶而跳舞，或者它们的卵子相对于它们的体型有多大。我们只是触及了表面，研究了变化的一个方面，但还有更多。”

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.

梅里认为，胸骨的形状和结构会影响不同种类鸟类的呼吸方式。她还说，不同的飞行方式意味着不同物种对资源的需求不同。

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

深入研究鸟类今天的飞行方式可以告诉科学家很多关于它们在数百万年中是如何进化的。

Lowi-Merri: So, birds evolved from dinosaurs… 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.

洛伊·梅里：所以，鸟类是从恐龙进化而来的……我们并不确切知道哪些鸟类化石和哪些恐龙能够飞行。但是，更好地了解鸟类今天是如何飞行的，这是完成恐龙如何在世界上移动的图片的关键。

梅里计划下一步深入研究鸟类化石，部分是为了进一步了解飞行的起源。

Lowi-Merri: The thing about fossil birds is that a lot of them are flattened into rock slabs. 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.

洛伊·梅里：关于鸟类化石的一点是，它们中的很多都被夷为平地。但是有那么多令人惊叹的鸟类化石，尤其是来自中国…。因此，必须对它们进行稍微不同的研究，因为它们可能无法像现代鸟类胸骨那样，将它们置于三维环境中。

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.

不过，梅里说，就目前而言，她对从窗户飞过、在安大略省后院的树枝上占主导地位的雀形目小鸟的看法有所不同。

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 predators 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 metabolism and different food sources and how they use that in their body would be very different.

洛伊·梅里：它们大多是连续拍打的鸟类。它们飞得很快。他们从一个分支转移到另一个分支。他们试图远离捕食者，获取一些食物，无论是昆虫还是浆果。这让我想到了它们的骨架是如何构造的，以及它们的肌肉是如何工作的，与在高空翱翔的鹰有很大不同。因此，它们需要不同的新陈代谢和不同的食物来源，它们在体内的使用方式也会非常不同。