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Question 38·Medium·Central Ideas and Details

For decades, scientists believed that monarch butterflies in the eastern United States migrated exclusively to the mountains of central Mexico to overwinter. However, recent tracking data reveal that a small but significant number of these butterflies spend the winter along the Gulf Coast, sheltered in coastal forests. The researchers attribute this shift to the expansion of ornamental gardens that provide the butterflies with food plants year-round. While the population overwintering in Mexico remains large, the discovery indicates that monarch migration routes are more flexible than previously assumed.

According to the passage, what have recent tracking data revealed about some monarch butterflies?