Hibernation and Migration
Hibernation and migration are adaptations for animals to survive winter months when food is not available. Hibernation is when animals rest or remain asleep during the entire winter. Migration is the movement of animals from one place to another. The main reason an animal hibernates or migrates is due to the lack of food, which occurs during the winter months due to the cold weather.
There are different kinds of hibernation. Some animals sleep so deeply, they are impossible to wake up, like the woodchuck, skunk, and bat. Some of them are light sleepers like raccoons, skunks, and opossums that wake up during the winter to eat. Many bears take long rests and also lightly sleep during the winter months.
In the fall, animals get ready to hibernate by preparing for the winter. They eat extra food and begin storing it as body fat. They use this fat for energy while hibernating. Some animals store food like nuts and acorns to eat later in the winter. During hibernation an animal's body temperature drops, heartbeat slows down, and it uses very little energy. In fact, the woodchuck's heart rate drops to only 4 or 5 beats per minute. If temperatures turn warm during the winter, the animals end up using more energy, wake up early, and then have no food to eat.
The places animals hibernate in the winter include dens, burrows, hollow logs, or in openings between rocks. A den is prepared by lining it with leaves and mud to keep out the cold. Polar bears dig tunnels in the snow. Snakes, turtles, and frogs hibernate underground, because they are cold-blooded and need to protect themselves from the cold. Frogs and turtles get oxygen from air trapped inside the mud. In the spring when the sun warms the mud, they know that winter has passed and they end their hibernation. Goldfish living in outdoor ponds hibernate by floating at the bottom of the pond below the winter ice. Some fish, like carp, spend the winter partly buried in lake mud. Other animals, like the little brown bat, first have to migrate to a new place before they hibernate. They live in trees in warm months, but in cold weather they migrate to caves where it is warmer.
Animals also migrate to other areas during the winter months. Many birds fly long distances to escape the cold winter, like the Arctic tern from the North Pole that flies South to Antarctica. Some birds in the far south of South America, Australia and Africa, migrate to the North, and others from east to west to coastal climates. The monarch butterfly travels south during the winter where there are flowers. A few animals must avoid the extreme heat so they migrate to cooler areas. Animals may also migrate to find a good habitat to raise their young.
Animals flying during the day use the sun as a compass, others make adjustments to their path of travel so it is not affected by the sun's movements. At night time, some birds may use the stars to help with migration. Birds and other animals such as sea turtles can find north and south because they are able to detect the Earth's magnetism. Storms, bad weather, pollution, tall buildings, and the birds becoming tired may also affect the birds during migration.
Like hibernating animals, migrators prepare ahead of time. Some birds double their weight, eat a lot to fuel their regular feather shedding and growth, and feathers must be in tiptop shape for the long trip.
In summary, there are many animals that hibernate or migrate during the winter months. The differences in an animal's behavior vary widely, but all of the animals have the same reason, to find food and survive the winter months.