But advances in feeding and flight alone 但仅靠进食与飞行上的进步

168. And that's not the only change.
     这还不只是唯一的变化
169. Teeth have been replaced by beaks...
     牙齿被喙取代
170. ...that allow them to feed on new diets.
     使其能够以新的食物为食
171. But advances in feeding and flight alone
     但仅靠进食与飞行上的进步
172. were not enough to ensure the future of the birds.
     并不足以确保鸟类有一个光明的未来
173. They also drew on a rather flamboyant ancient behavior,
     它们还依赖于 一种相当引人注目的古老行为
174. a behavior that ensures the survival of the fittest.
     这种行为能够确保最优秀者生存下来

来自《我们星球上的生命 第一季 第六集 Life on Our Planet S01E06 灰烬中重生》第 171 行