Summers in the far north can be a time of lush and lavish living for the animals—plenty of fresh new plant growth for the vegetarians, lots of insects and nectar for birds, berries and salmon for bears, and for wolves there's often an abundance of voles, mice, and snowshoe hares. The endless days of nonstop eating allow many animals the luxury of putting on fat.

But summers are fleeting and winters long—up to 8 months—and brutally cold. Temperatures can plunge to minus 70 degrees. Gales make it feel even colder, and deep or drifted snow can make simply moving around an energy-draining ordeal.

Of course, if you can fly, one choice is to opt-out of winter all together.

Alaska's migratory birds do just that. Some birds, like loons whose summer lakes are frozen in winter, only go as far as the coasts of Alaska, Washington, and Oregon. Robins only need to reach places with frost-free ground, so they can hunt for worms and insects. Other birds go for the relative warmth of the southern US, and some take advantage of the tropics and subtropics—enjoying two summers.

Arctic terns take migration to the ultimate extreme—after a summer in the far north they spend their "winter" in Antarctic waters, so these amazing birds live most of their lives in perpetual daylight.

But what about the animals who stay?

Some birds, like ptarmigan, stick it out through the long and unimaginably tough northern winters. And most other animals—the walkers and crawlers and swimmers—simply don't have the option of leaving.

To stay and tough it out—to survive at 40…50…60 degrees below and colder—animals have evolved some ingenious and fascinating adaptations.

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