送交者: AI 于 2006-6-08, 12:48:52:

My guess with two reasons. One is that a single leg of most birds is too thin or weak to support a whole body weight. The other is: all birds (including eagles) jump when taking off from ground to give enough room for wins to swing. So, jumping is the necessary nature of birds.

• good points - michiko (176 bytes) 2006-6-08, 15:13:31
• 那野鸭呢？那腿不壮，还需要起飞。为什么不跳着走路？ - Amsel (0 bytes) 2006-6-08, 14:03:35
  • 野鸭 never jump when taking off, it runs or paddles in waters - AI (49 bytes) 2006-6-08, 14:10:37
    • 是啊。许多禽类是在陆地上助跑或水面上划跑起飞的。不过越小型的越倾向于jump - 比目氏 (0 bytes) 2006-6-08, 18:53:08
• 那兔子呢？那腿够壮，也不用起飞。为什么也跳着走路？ - PoohHunny2 (0 bytes) 2006-6-08, 13:57:39
  • All land animals with four legs have almost same leg length. - AI (71 bytes) 2006-6-08, 14:07:44
    • What about humans and kingkongs? - whoami (0 bytes) 2006-6-08, 18:33:43

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