In this set of materials both the writer and lecturer cover the issue of bird migration. Regarding the issue, the speaker contradicts the reading passage's explanation that scientists have developed several theories to explain how birds migrate.
First, the lecturer insists that the sun and the stars are not seen all time. Too many clouds could cover the sun in day, and the sun cannot be seen in night. The stars is the same in the night, they could be disguised from the clouds. Moreover, birds cannot find well the sun and the stars in the bad weather. This opposes the reading passage's assertion that the stars and the sun play a key role in a bird's navigation.
Second, the speaker argues that birds can find the place when they use first route. To be more specific, landmarks do not exist, but they can find their place. This contradicts the reading passage's claim that birds use the landmarks and find their way.
Third, the professor maintains that the theory that birds have natural inner compasses is not sufficient. This is because birds feel the north and south direction, but the east and western are not recognized. This casts doubt on the reading passage's explanation that birds use their natural sense and find their way. |