Key to Passage 3

1. (D) The passage mentions that some species are well adapted to harsh living conditions ("suited to the difficult conditions"). It can be understood that such birds don't migrate south.

2. (D) The word "those" refers to the species of birds that find moving south in the winter advantageous.

3. (D) According to the passage, "changes in the weather can trigger the start of the journey south," or "the onset of migration."

4. (A) When fat "accumulates" under the skin, it "builds up."

5. (D) The passage does not mention birds migrating east-west toward a hotter climate.

6. (B) "Precisely" refers to an action that is performed "exactly" without error.

7. (C) Since the polarization patterns are visible at sunset and the passage mentions patterns in sunlight, we can infer that they "are invisible at night."

8. (B) The bowtie shape of the pattern has "fuzzy" ends which are reminiscent of a brush.

9. (A) The term "subjected" here means that the birds were "exposed" to the projection on the inside of the planetarium.

10. (C) According to paragraph 6, some research using projections on the planetarium ceiling indicates the birds are guided by the constellations.

11. (A) The highlighted sentence means the same as "Birds needing to orientate seemed to use the information...  from the stars that rotate around Polaris."

12. (B) The word "this" refers to the fact that when fewer stars are visible on the planetarium ceiling, the birds' sense of direction worsened.

13. The second square. The particular landscapes such as river valleys and shapes of hills are examples of topographic features. This would follow the sentence that mentions topographic features.

14. (B) (E) (F)

The main ideas from the passage are all theories that scientists have studied in their attempt to understand the methods birds use to migrate. These theories are that birds may determine direction:

-- through detection of the gradations of polarization patterns in sunlight ("Birds' ability to detect... ")

-- through the rotation of stars around a fixed position ("The star patterns... ")

-- through knowledge of landscape features ("Birds may use... ")