Which of the following is an example of migration?

A.) Woodchucks store up extra energy for winter, then sleep until the warm weather returns.

B.) During the dry season, elephants travel long distances to reach rivers and other water sources.

C.) Over winter, a seed remains unchanged within the soil, not germinating until the temperature warms.

D.) Baby birds remain in their nests until they grow the feathers needed for flying, at which point they become fledglings.