They journey hundreds -- sometimes thousands -- of miles for food, shelter and to give birth.
And the annual wildlife migrations that take place around the world aren't just spectacular displays of nature, they're once-in-a-lifetime travel opportunities.
Bald eagles, British Columbia, Canada
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Not a vulturous scene from "The Jungle Book," a migratory scene from British Columbia.
Bald eagles are the only sea eagles endemic to North America, and each winter they gather in droves on the branches of Douglas fir, hemlock and cottonwood in Brackendale, British Columbia, a community just north of Squamish (halfway between Vancouver and Whistler).
The eagles come to feed on salmon that swim up Brackendale's glacial-fed rivers to spawn.
While the best time to see them is mid-November through mid-February, the eagles are at their peak in January and typically average around 1,500 a year, with a record-setting high of 3,769 in 1994.
One of the best ways to view them is on a half-day river rafting float down the Squamish River with Brackendale's Sunwolf Lodge. The trip costs US$100; overnight packages -- including cabin stays -- begin at US$285, www.sunwolf.net
Wildebeest, East Africa
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Just 1,800 miles to go, before the journey starts all over again.
The annual wildebeest migration between Tanzania and Kenya involves up to 1.5 million of these antelope traversing vast stretches of open plains in search of fresh, mineral-rich grasslands.
This isn't so much a time-oriented migration as it is a continual search for food, over a round-journey of 1,800 miles.
Along with zebra, gazelle and eland -- who join the wildebeest on their travels -- the journey attracts thousands of spectators, not to mention lions, leopards and carnivorous crocodiles, that wait for a chance to attack the prey.
While the animals move year-round, the start of the dry season -- typically late June and July -- is the best time for viewing wildebeest in Kenya's Masai Mara.
The reserve and its surrounds have dozens of camps at the center of the action. One of the best is Kicheche Valley Camp in the Naboisho Conservancy, just beyond Masai Mara's borders. kicheche.com
Emperor penguins, Antarctica
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Emperor penguins escorted by an elephant seal as they march.
National Geographic's 2005 documentary, “March of the Penguins,” introduced the world to Antarctica's annual emperor penguin migration: thousands of gray-backed, white-belled birds up to four feet in height making multiple journeys across a massive ice sheet -- at the peak of winter -- in a story of parenthood and birth.
Their arduous expedition is instinctual and remarkable to see, especially against Antarctica's stark white scenery.
This best time for viewing the emperor penguin migration is typically October through early December.
Premier travel company Adventure Network International offers nine-day expeditions to one of the continent's emperor penguin rookeries, though the US$40,200 price tag is a tad steep, www.adventure-network.com; more affordable is Quark Expeditions, which runs cruises to Antarctica that coincide with the annual event, www.quarkexpeditions.com
Monarch butterflies, California, United States
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Santa Claus isn't the only arrival in California during December.
Every October, tens of thousands of monarch butterflies arrive in Pacific Grove, Calif., to nest for the winter. These orange and black beauties crowd the coastal city's Monterey pines and eucalyptus trees, roosting in the exact same spots their ancestors did.
The sight is most spectacular midday when the sun is at its brightest, shining through the monarchs' wings and illuminating them like stained-glass windows.
Pacific Grove hosts a Butterfly Parade each October to welcome the seasonal residents, whose numbers peak during December and January.
Butterfly docents are on hand at tPacific Grove's Monarch Grove Sanctuary throughout the season to offer info and details. www.pacificgrove.org
Bats, Texas, United States
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Not a happy scene if you're a mayfly.
Each evening from March through October, the skies of downtown Austin, Texas, become awash with the winged bodies of anywhere from 750,000 to 1.5 million Mexican free-tailed bats.
They fly from their roosts beneath the city's Congress Avenue bridge like an oscillating ink stain, embarking on a search for food.
It's the largest urban bat colony in North America and it's estimated that they consume up to 30,000 pounds of insects nightly.
In the beginning, the bats are mostly pregnant females who've journeyed north from Mexico to give birth, typically around June and July. The sight becomes even more spectacular in August, when the babies join their mothers in flight.
Hundreds of spectators take to the southeast slopes of the Congress Avenue bridge each evening to catch the bats as they emerge, usually when the sun begins to set. Take a blanket and join them, or book an hour-long tour on Lady Bird Lake with Lone Star Riverboat to watch from the water. www.lonestarriverboat.com
Arctic caribou, North America
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Where 100,000 caribou go, wolves are sure to follow.
The mass migration of North America's Porcupine caribou (the name derives from the Porcupine River that runs through Alaska and the Yukon), is some feat: a grueling 1,500-plus-mile journey from Canada and Alaska to the Arctic Refuge coastal plain and back -- using various routes -- in search of nutrients and insect relief.
The number of Porcupine caribou arriving at Alaska's Arctic National Wildlife Refuge can reach upward of 100,000.
The event also sparks the arrival of bear, wolves and wolverines.
Arctic Wild leads an eight-day photography adventure into the Arctic National Wildlife Refuge in June, when the population of Porcupine caribou is typically at its peak. Prices are US$4,500 per person. www.arcticwild.com
Whale sharks, Mexico
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One Mexico tourist that's not here for the beer and burritos.
Though enormous in size (whale sharks can reach more than 40 feet in length and weigh up to 15 tons), the largest fish in the sea is also completely docile and typically solitary, which makes the arrival of hundreds of them off Mexico's eastern coast an extraordinary sight.
Every summer these spotted and striped fish arrive in the Gulf of Mexico from the Caribbean to feed on plankton, meandering from side to side as they search. They typically hang around from June through mid-September.
Searious Diving offers boat trips to snorkel with whale sharks in the waters north of Isla Mujeres, one of the great fish's two local hubs. Prices begin at US$125, www.islawhalesharks.com
Flamingos, Kenya
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Just so the wildebeest don't get all the attention, these guys summer in East Africa, too.
Between April and June, Kenya's Lake Nakuru explodes with color, its shallow waters overrun with long-legged lesser pink flamingos who've come to feed on the lake's blue-green algae.
It's been described as a full-on fuchsia feast.
While their numbers have fluctuated in recent years -- from 6,500 to as many as 250,000 -- the display remains spectacular, especially if you have the opportunity to spot them soaring in flocks overhead.
Lion Trail Safaris runs day trips from Nairobi to the alkaline lake, located about two hours north of the city. Prices begin at US$175, www.liontrailssafaris.com
Red crabs, Christmas Island, Australia
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Millions of individuals, all with one birthday. Each year millions of bright red land crabs leave their burrow homes on Australia's Christmas Island and start a long, laborious trek toward the sea.
They descend cliffs, climb banks and maneuver around obstacles to reach the shoreline and lay their eggs, eventually returning to the island's central plateau with their offspring in tow.
The synchronized migration resembles a crimson-colored river undulating across the island and can last up to 18 days.
The event typically takes place in November or December (the crabs will only move when it's raining) and coincides with the turning of high tide and the arrival of the waning moon.
Island Explorer Holidays offer a round-trip adventure from Perth to Christmas Island to watch the phenomenon. Prices begin at US$1,500, www.islandexplorer.com.au
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