本篇文章共分 6 段，針對食草動物在一望無垠的草原進食時所面對的安全性問題，說明成群動物與掠食者之間的互動關係，並分析牧群團體所能提供的安全保障與可能漏洞。

本篇考題英文原文與對應之中文翻譯整理如下。練習作答解題時若有對語意不清楚之處，請仔細查閱對照，以提升閱讀理解能力。

How Herding Can Provide Safety 牧群如何提供安全

1. 草食動物進食的安全疑慮

   In open grasslands there is no place for a large animal to hide. Thus a watchful grazing animal will see the slight movement that betrays the presence of a predator long before it is close enough to launch an attack. It sounds as though the hunters (predators) stand no chance at all. Unfortunately for the grazers, life is not so simple, however. A grazing animal must lower its head and look at the ground to feed. Its attention may be occupied for only a few seconds before it raises its head and resumes its watch while chewing the food it took, but hunters are patient and skillful and are concentrating intensely. Those few seconds provide time enough to advance a few steps and then freeze, body flattened against the ground. It may take hours, but eventually these repeated small advances will put the hunter within range—close enough to outrun its prey—and the long time the hunt has taken will have been worthwhile, because the resulting feast will be highly nutritious.

   在開闊的草地上，大型動物沒有地方可以藏身。因此，警惕的食草動物會在捕食者發動攻擊之前很久，就看到洩漏捕食者存在的輕微動作。這聽起來好像獵人（掠食者）根本沒有機會。然而，對吃草的動物來說，生活並不那麼簡單。吃草的動物必須低下頭來，看著地面進食。它的注意力可能只被佔用了幾秒鐘，然後就會抬起頭來，繼續看，同時咀嚼它取得的食物：但獵人是有耐心和技巧的，而且注意力非常集中。這幾秒鐘的時間足以讓它前進幾步，然後定住，身體平貼在地上。這可能需要幾個小時：但最終這些反覆的小規模前進將使獵人進入攻擊距離之內—近到足以跑得快過獵物—而狩獵所花費的漫長時間將是值得的，因為由此產生的盛宴將是非常有營養的。

2. 掠食者與獵物的數量關係

   Clearly the grazers are at a disadvantage, because while they eat they are vulnerable to attack. The hunters also have a weakness, however, and it is one that allows the grazers to survive. Hunters can attack only one prey animal at a time. This applies even to the predators that hunt as a team, such as lionesses, wolves, and hunting dogs. Their hunt involves running down or ambushing an individual. Teamwork allows them to hunt animals much bigger and stronger than themselves and to hunt more successfully, but it does not allow them to attack more than one individual at a time.

   顯然，食草動物處於不利地位，因為他們在吃東西的時候很容易受到攻擊。然而，獵人也有一個弱點：而這個弱點使食草者得以生存。獵人一次只能攻擊一個獵物。這甚至適用於那些以團隊形式狩獵的食肉動物，如母獅、狼和獵狗。它們的狩獵活動包括撞倒或伏擊單一個體。團隊合作使它們能夠獵取比自己大得多、強得多的動物，並使狩獵更加成功，但這並不允許它們一次攻擊一個以上的個體。

3. 牧群的安全性

   The grazers exploit this weakness by making it as difficult as they can for the predators to choose an individual as a target. They do not graze alone, scattered widely across the landscape, but together as a herd. The approaching hunter sees not a solitary animal, but a crowd of animals, all of them moving, so they are constantly crossing and recrossing each other’s paths. No sooner does the hunter choose an individual than another animal has crossed in front of it and the target has disappeared into the herd. From the hunter's point of view this is highly confusing behavior—as, indeed, it is meant to be.

   食草者利用此一弱點，盡可能地使捕食者難以選擇某個個體作為目標。它們不是單獨吃草，意即廣泛地散佈於各處，而是作為一個群落一起吃草。靠近的獵人看到的不是一隻孤單的動物，而是一群動物，它們都在移動，所以它們不斷地穿越和重新穿越彼此的路徑。獵人剛選定一個個體，另一隻動物就從它面前穿過，目標就消失在獸群中了。從獵人的角度來看，這是非常令人困惑的行為—事實上，這就是原本的目的。

4. 牧群偕同聯防之利

   There is another advantage to the grazers: A herd is much more alert than a solitary animal. An animal has to relax its guard while it is taking food, but in a herd there are at any time some animals with their heads down, biting, and others, with their heads up, watching. What is more, those with their heads up are looking in different directions so that together they are alert to any movement anywhere on the landscape around them. There is no way for a hunter to approach a herd unobserved. When a member of the herd spots trouble, it starts to move away. Other members of the herd move with it and the entire herd starts to move. If the trouble is serious and close, the herd will run. The individual raising the alarm is simply protecting itself but in doing so it is warning all of the others.

   食草者還有一個優勢：牧群比獨處動物更有警惕性。動物在取食時必須放鬆警惕；但在獸群中，隨時都有一些動物低著頭在吃草，而另一些則抬著頭在觀察。更重要的是，那些抬著頭的動物在看不同的方向，所以它們一起對周圍任何地方的移動都很警覺。獵人不可能在無人注意的情況下接近獸群。當獸群中的一個成員發現問題時，它就開始移動。牧群中的其他成員也跟著移動，整個牧群開始移動。如果麻煩很嚴重而且緊迫，整個牧群就會奔跑。發出警報的個體只是在保護自己，但這樣做是在警告所有其他成員。

5. 落單動物成為獵物

   Herding is highly successful, provided members of the herd stay together in a tight bunch. The hunter moves with the herd, watching for an individual to wander away from the others. When that happens, it tries to move between that individual and the rest of the herd, preventing it from rejoining. Once it has done that the hunter has a good chance of making a kill. If the herd starts to run, a solitary hunter may abandon the chase, but a pack of wolves or hunting dogs will regard the running herd of animals as an opportunity and set off in pursuit. As the herd runs, one or two old or sick animals, or young animals that become separated from their mothers, may fall behind.

   只要牧群的成員緊緊靠在一起，牧群就會非常成功。獵人會跟著獸群一起移動，觀察某個個體是否離開了其他個體。當這種情況發生時，它就會試圖在該個體和獸群的其他成員之間移動，以防止它重新加入。一旦它做到了這一點，獵人就有很大的機會將其獵殺。如果獸群開始奔跑，單打獨鬥的獵人可能會放棄追逐，但一群狼或獵狗會把奔跑的獸群看作是一個機會，並開始追逐。在獸群奔跑的過程中，一兩隻老弱病殘的動物或與母親走散的小動物可能會掉隊。

6. 牧群重獲安寧

   As soon as the hunter or hunters seize their prey, they lose interest in all other grazers since then they, too, must concentrate on eating, at which point the herd stops running, those who were left behind rejoin the group, and they all resume grazing.

   一旦獵人抓住了他們的獵物，他們就會對所有其他吃草的動物失去興趣，因為這時他們也必須集中精力吃東西，這時獸群就會停止奔跑，那些被落下的動物就會重新回到群體中，然後他們都會恢復吃草。