When the northern end of the Earth is tilted away from the sun, many animals start to make their annual trek north. For those crossing North America, that means overcoming human obstacles: pronghorn antelope head for Grand Teton, but ranch fences and highways stretch across their path; snow geese rest along their Missouri flyway, where they trade the risks of hunters for the abundant food found throughout the farm belt. Winter in the Northern Hemisphere also means warm water in the south, and it’s the perfect time for gentoo penguins to find land on which to breed; they’re the world’s fastest penguin, but leopard seals still chase them down as they return to the water. And at the Equator, where the temperature mostly stays constant, gray whales relax with their calves before embarking on a long swim to the Bering Sea for summer. The road ahead is riddled with dangers – and not everyone will make it safely – but preserving their freedom to make the journey is up to us all.

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Some animals migrate from the moment that they’re born, and their first journey is almost always their most challenging. For female turtle hatchlings on Mexico’s Pacific coast, that means running a gauntlet of predators. They’ll spend 15 years at sea before returning to lay their own eggs on the very same beach. For the billions of baby red crablets of Christmas Island, it’s a chaotic journey past cannibal crabs and across manmade obstacles to get back to the forest. Young pumas must learn to hunt from their mothers before venturing out in search of their own territory, and elephant seal pups have to master the art of swimming before leaving the safety of the beach and striking out on their own. But for a few species, there’s an even bigger problem: what do you do when the environment your ancestors migrated through for millions of years has changed – and that change is putting your survival at risk?

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It’s summer, and our solar-powered planet is bustling with animals on the move. Snow geese are breeding in the warming Arctic tundra, and tadpoles in Vancouver are trying to grow into toads; whale sharks are gathering to feed in the Persian Gulf, and in Europe, the honeybees are hard at work building new hives. In Alaska, thousands of sockeye salmon have flushed bright red to make their journey upstream to spawn, an annual event that freshwater seals and grizzly bears depend on to fatten up for winter. With virtually no sea ice remaining in the Arctic, polar bears now spend most of their days swimming, and a young cub who struggles to keep up with his mother may be left behind. But the most treacherous journey of all can be found on the plains of the Serengeti, where wildebeest and zebras must cross the “River of Death” to find fresh lands on which to graze. Many of them will drown in the stampede to make it through the water – if lions and giant crocodiles don’t eat them first.

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Migration is the oldest and most vital survival strategy in the animal kingdom, and every day, billions of creatures great and small are making extraordinary journeys. In the peak of dry season, the barren savannah of Botswana drives a megaherd of cape buffalo to a remote wash where hungry lions await their arrival, while in Ethiopia, the largest swarm of desert locusts in recent memory takes to the sky. As the sun warms the oceans, massive algae blooms summon humpback whales to the Bering Sea to feed, but polar bears and walrus in the Arctic struggle to navigate melting sea ice. Springtime also brings new life, as tiny ancient murrelet chicks emerge from their nests in the Pacific Northwest and race like clockwork toys towards the sea – but on a distant island north of Hawaii, tons of plastic are impacting the life cycle of Laysan albatross chicks, and tiger sharks circle in the shallows to feed on chicks that live long enough to take their first flight.

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