Using the examples in the lecture, explain how the position of birds' eyes is critical to their survival.
请用课上所举例子解释说明为什么鸟类的眼睛对它们的生存至关重要。
Listen to part of a lecture in a biology class.
请听生物课上的部分内容。

Birds have some of the best vision capabilities in the animal kingdom.
在动物王国中，鸟类的视力是最好的之一。
Some birds species have vision that is eight to ten times greater than humans.
有些鸟类的视力比人类的要好八到十倍。
Overall, a bird's eyes are extremely important for its survival.
总的来说，一只鸟的眼睛对于它的存亡极其重要。
One aspect of bird's eyes that plays a role in helping them survive,
鸟的眼睛在帮助它们生存方面起作用的，
in other words to find food or to avoid predators, is the position of the eyes in the skull.
换句话说，能够帮助它们找到食物或者躲避天敌的其中一部分，就是它们的眼睛在头骨中的位置。
Some birds have eyes that face forward on the skull, kind of similar to how human's eyes are positioned.
有些鸟类的眼睛朝着头骨前方生长，有点像人类眼睛的生长位置。
Forward-facing eyes allow a bird to clearly see and judge distances
眼睛朝前使得鸟类可以清楚地看见远方并判断距离，
because it can focus on objects with both of its eyes, and correctly perceive height, width and depth.
因为它可以两只眼睛一起关注物体，并且准确地感知到高度、宽度和深度。
One type of bird with eyes positioned in the front of the skull is the hawk.
眼睛生长在头骨前方的其中一种鸟类就是鹰。
Hawks eat animals like mice. Hawks have such good eye sight
鹰以老鼠这类小型动物为食。它们的视力非常好，
that they can spot a tiny mouse in the field from high up in the air.
可以从高空中捕捉到田野里一只小老鼠的踪影。
They spot the mouse and swoop down to catch it.
它们看见老鼠后便会俯冲下来捉住它。
Without such good eye sight, they would not be able to spot or catch their food.
没有这么好的视力的话，它们就不可能看见或者捉到猎物了。
Other birds have eyes that are located on each side of the skull.
也有其他鸟类的眼睛生长在头骨两侧。
This positioning of the eyes can help a bird to avoid predators.
眼睛生长在这种位置可以帮助鸟类躲避捕食者。
Instead of just seeing what's directly in front,
除了只能看见正前方，
they can see things that are on either side, permitting them to watch for danger in all directions.
它们还看得见身体两侧的事物。这样它们就能察觉到来自任何方位的危险了。
Imagine a duck wading near the edge of a lake.
想象一下一只鸭子正凫在湖岸边。
It needs to spend time eating grasses and insects,
它需要一些时间吃草和昆虫，
but it also is on constant lookout for danger from its predator, like the fox.
但它同时也时刻警惕着，不断察看有没有捕食者的踪影，比如狐狸。
An eye on each side of the duck's head allows it to see a fox approaching from either side.
鸭子头上一边一只的眼睛使得它能从任意一边看见企图接近它的狐狸。
If it spots a fox, it can then fly away to safety.
一旦发现了狐狸的踪影，它就能立刻飞到安全的地方去。
The placement of the eyes are critical in helping the duck avoid predators.
眼睛的位置在帮助鸭子躲避捕食者时至关重要。