Animals

Largest Beaver Dam Seen From Space

The dam in northern Canada spans 2,800 feet and has likely been under beavers' construction since the mid-1970s.

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A Canadian ecologist has discovered the world's largest beaver dam in a remote area of northern Alberta, an animal-made structure so large it is visible from space.

Researcher Jean Thie said Wednesday he used satellite imagery and Google Earth software to locate the dam, which is about 850 meters (2,800 feet) long on the southern edge of Wood Buffalo National Park.

Average beaver dams in Canada are 10 to 100 meters long, and only rarely do they reach 500 meters.

First discovered in October 2007, the gigantic dam is located in a virtually inaccessible part of the park south of Lac Claire, about 190 kilometers (120 miles) northeast of Fort McMurray.

Construction of the dam likely started in the mid-1970s, said Thie, who made his discovery quite by accident while tracking melting permafrost in Canada's far north.

"Several generations of beavers worked on it and it's still growing," he said.

Mike Keizer, spokesman for the park, said rangers flew over the heavily forested marshlands last year to try to "have a look." They found significant vegetation growing on the dam itself, suggesting it's very old, he said.

"A new dam would have a lot of fresh sticks," Keizer explained. "This one has grasses growing on it and it's very green."

Part of the dam may have been created by naturally felled trees, and the beavers "opportunistically filled in the gaps."

Thie said he recently identified two smaller dams sprouting at either side of the main dam. In 10 years, all three structures could merge into a mega-dam measuring just short of a kilometer in length, he said.

The region is flat, so the beavers would have had to build a massive structure to stem wetland water flows, Thie said, noting that the dam was visible in NASA satellite imagery from the 1990s.

"It's a unique phenomenon," he said. "Beaver dams are among the few animal-made structures visible from space."

North American beavers build dams to create deep, still pools of water to protect against predators, and to float food and building materials.

A 652-meter structure in Three Forks, Montana previously held the record for world's largest beaver dam.

Thie said he also found evidence that beavers were repopulating old habitats after being hunted extensively for pelts in past centuries.

"They're invading their old territories in a remarkable way in Canada," he said. "I found huge dams throughout Canada, and beaver colonies with up to 100 of them in a square kilometer."

"They're re-engineering the landscape," he said.

The beaver dam in Canada's Wood Buffalo National Park, as seen from above.

This week, millions of college kids are preparing to migrate to warmer regions for their spring breaks. Animals are also taking advantage of the warmer weather and beginning their spring migrations.

Birds are the champions of migrations, but butterflies, snakes and even salamanders migrate in the spring. For nature-loving humans with cabin fever, the spring migrations can be the year's first chance to take in the wonder of wildlife.

The American robin, the classic harbinger of spring, has already made its spring trip to the backyards of most in the United States. The first robins of the year were recorded in January in the south, and birds have already been seen as far north as Maine.

Snow geese

Nature's road ragers, geese, migrate in noisy, honky Vs that help the birds reduce wind drag and avoid collisions.

One subspecies, the lesser snow goose, has learned to make use of human-made pit stops on its long aerial drive, gorging on waste grain from farm fields. Many of the birds make their southbound trip through the central United States, which also boasts some of the best farmland in the world. Snow geese used to survive on the humble roots of marsh grasses, but have adapted to rice, wheat, corn and other grains left behind after the harvest.

Swans

Spring breakers head for the coasts, but tundra swans swoop into the east and west coasts of the United States in the fall. Now, the birds are heading back north. Like spring break revelers making poor choices, the swans like to get higher than kites while they travel, as high as 2.5 kilometers (nearly 8,000 feet) during their 6,500-kilometer (4,000-mile) trek north.

Tundra swans

Tundra swans head further north than their larger cousins the trumpeter swan, but they may be losing breeding ground due to climate change. Tundra swans breed in the far north. The birds depend on the frigid temperatures to keep the larger trumpeter swans from muscling in on their territory.

Trumpeter cygnets need at least 145 days to grow strong enough to make the migration south to ponds that don't freeze over in the winter. However, the Arctic is warming, which is allowing trumpeters to move north to breed, according to a study published in BioOne.

Sandhill cranes

Some over-partying super seniors may be making their fifth or sixth spring break road trip, but that is nothing in comparison to sandhill cranes.

Fossils provide evidence that sandhill cranes are one of the most ancient species of living birds, going back at least 2.5 million years.

Eighty percent of the world’s sandhill crane population makes a stop to fatten up in Nebraska every spring. Approximately 400-500,000 cranes use a 75-mile stretch of the Platte River’s sand hills as a stopping point during their migration north to breed in Alaska and Canada.

Kirtland's warblers

Kirtland's warblers get to chill out in the Bahamas in spring. This small, yellow-breasted bird escapes the harsh Michigan winter by migrating south from August-October.

Until 1995, the birds returned to breed in only a small area in the north of Michigan's Lower Peninsula. The birds depended on large expanses of jack pine for their breeding territory. Loggers leveled much of the jack pine forest in the southern Great Lakes region in the 1800s. By the middle of the last century, the loss of that breeding habitat nearly drove the warblers to extinction.

Now though, the Kirtland's warbler has made a stunning comeback from the brink of extinction. The birds have adapted to use jack pine forests that are being managed for lumber and paper production.

Scarlet tanagers

Scarlet tanagers also winter in the balmy tropics. They make an even longer trek to flee the frosts of the eastern United States. These beautiful bright red migrants travel through Mexico, Central America and eventually reach South America each autumn.

The tanagers are now on their way back to U.S. forests to look for breeding spots. The birds will set up their spring fiesta by late April or May.

Monarch Butterflies

Mexico is as popular with migrating animals as it is with spring breakers. And it’s not just birds taking a break south of the border. Many monarch butterflies migrate to the highland forests in Mexico, where they spend the winters. The butterflies are now on their way back and will soon be feeding on milkweed plants from coast to coast.

Spotted salamanders

Sexual hijinks and spring break trips go hand in hand. In early spring, spotted salamanders feel a need to breed and stage the amphibian version of an orgy.

When the weather starts to get warmer, the salamanders awake from hibernation and head for temporary pools of water. The salamanders breed in the temporary spring ponds because fish would eat their tadpoles if they used permanent bodies of water. The downside is that the salamanders need to rush for the breeding sites before they dry up.

Copperheads

Copperheads wake up from hibernation in large groups in rocky shelters. In spring, they need to split up to find food.

Rowdy guys are a notorious spring break problem and male copperheads can be just as feisty. Male copperheads will wrestle with each other to impress the ladies, joining the throngs of spring breakers from all species.