Bird Migration

Hibernation and Migration


The word “hibernation” comes from the Latin word hibernare, which means, “to pass the winter.” Linked to the changing of the seasons, from the warmth of summer and early autumn to the onset of the chill of winter, hibernation is a physical state that many animals adopt to converse energy. By remaining inactive in burrows, buried nests, and hollows, hibernators’ inactivity slows their metabolism and reduces their body temperature for days, weeks or even months at a time, helping them to survive when food supplies are low. Hibernation is therefore an almost sleep-state that many animal species have evolved to help them to weather long stretches of time without needing to drink, eat or urinate.

Although some fish, amphibians, birds and reptiles are known to lie dormant during cold winter months, according to Don Wilson, a curator emeritus of vertebrate zoology at the Smithsonian National Museum of Natural History in America, “hibernation is generally associated with (warm blooded) mammals… During times of the year when that energy source is missing — especially in northern climates — one coping mechanism is to just shut down. They’ll feed heavily during the few months when food is plentiful and build up fat, then go to sleep and live off their fat reserves.”

The fat which hibernating mammals accumulate is known as “brown fat.” Mammals store this fat on their backs and around their shoulder blades as well as in their stomachs over the summer. As the animals hibernate, the dormant body can live off this brown fat, therefore ensuring that they stay alive during the harshest conditions. Female polar bears not only survive off this brown fat themselves, but often go into hibernation while pregnant, and use their reserves to feed not just themselves, but any cubs that may be born whilst they are in their annual sleep-state.

While many creatures hibernate, many others migrate. Whereas hibernation prevents animals from having to forage for food and be able to have more comfortable living conditions in winter, migration sends others on a long journey to find food, often in a much warmer climate. Migration can also be triggered by an animal’s need to breed. Humpback whales for example, travel as much as 5,000 miles to breed, while a shorebird called the bar-tailed godwit holds the record for the longest nonstop flight. It will fly an incredible 6,835 miles in eight days to find both food and a mate ( the route is shown above ). In Africa, zebras and wildebeest travel on a 300 mile round-trip to stay ahead of the rain and keep dry and have plenty of food.

Although migration and hibernation are both very different animal lifestyles and lifecycles, they are driven by the same force; the instinct to survive. The need for food, for safe warm, dry places to live, and the need to ensure the continuation of their species.

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Dr Kathryn Bates is a graduate of archaeology and history. She has excavated across the world as an archaeologist, and tutored medieval history at Leicester University. She joined the administrative team at Oxford Open Learning twelve years ago. Alongside her distance learning work, Dr Bates is a bestselling novelist, and an itinerant creative writing tutor for primary school children.

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