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PP^ because the - • water freezes, and these birds need open water to survive- Birds that •dt* mostly insects leave North Amftjfca and go South to the Tropics, becatlse there is no food for them in the north in winter.
This question has fascinated scientists for centuries, and we are only beginning to know how some birds find their way during long migrations. Birds are bom knowing that they must migrate, but knowing that is not the same as knowing how to get from a backyard in Virginia to a jungle in Brazil or from a sea cliff in Alaska to a feeding ground in the Atlantic.
It is now known that some birds are bom with a "star map" coded into their brains that allows them to navigate by the position of the stars and the moon. Some birds use the earth's magnetic field to find their way, and some use subsonic sound, the lowlevel noise created by ocean waves.
Still others, fike geese, make their migrations in family groups, led always, by an. older bird that has
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