Definition: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Notice the differences in the species' beaks in Figure 18.13. Evolution in response to natural selection based on specific food sources in each new habitat led to evolution of a different beak suited to the specific food source. The seed-eating bird has a thicker, stronger beak which is suited to break hard nuts. The nectar-eating birds have long beaks to dip into flowers to reach the nectar. The insect-eating birds have beaks like swords, appropriate for stabbing and impaling insects. Darwin's finches are another example of adaptive radiation in an archipelago. Answer: beaks
Output:
Evolutionary adaptation is evidenced by different shapes of what structures in birds with different food preferences?