Another kind of seasonal migration is altitudinal migration, which is where animals move vertically rather than to a different region of the earth. They go up the mountain in the spring and down it in the winter. The Dall Sheep of the American Rocky Mountains are good examples of this. In the spring, they follow the menlting snow up to higher elevations, where they can feed on fresh plant growth and be safer from enermies, and then in the fall, when the snow begins to cover the mountain tops, they work their way back down to lower areas that are free of snow and more protected from the elements.
In regions with irregular climate patterns, some animals are nomadic――that is, they just kind of wander around from one area to another as, for instance, the rains bring fresh plant growth to these different places. The gnus, antelopes and other grazing animals of east Africa do this, wandering around the famous Serengeti Plain to where the grass is greenest.
Now most such migrations are undergone in search of food and water, but there are also reproductive migrations, where the purpose is to find a habitat that is safe and secure for the young. This accounts for the migration, for instance, of Grey Whales, who leave the food-rich waters of the north Pacific and travel to the protected waters of the Gulf of California to give birth.
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