What is the overall theme of the text discussing the migration of Tule geese?

• A. The effect of weather on migrating fish.
• B. The genetics of geese in captivity.
• C. The history of Tule geese in science.
• D. The impact of environmental factors on animal behavior.

Answer: (D)

Environmental factors guide migration decisions, and the Tule geese text shows how weather patterns, food availability, and habitat changes influence when, where, and how these birds move. The main idea is that animal behavior, especially migration, is shaped by the surrounding environment—cues from weather, resource distribution, and landscapes—not by genetics alone or by studying historical aspects or other species. So the text’s theme centers on how environmental factors impact how birds behave during migration, which is why this option fits best.