Revealing the Secrets of the 'Winter World'

Book Explores Ingenious Ways Animals Survive in Cold Climes

Biologist and science writer Bernd Heinrich

Biologist Bernd Heinrich does much of his research from his hand-built log cabin in the snowy woods of Weld, Maine. Josh Rogosin, NPR hide caption

itoggle caption Josh Rogosin, NPR

The imprint left by the wings of a raven landing on the snow. Heinrich attracts ravens to the woods near his cabin by leaving out carcasses for the birds. Josh Rogosin, NPR hide caption

Enlarge image.
itoggle caption Josh Rogosin, NPR

An illustration of Golden-crowned kinglets from Winter World. Not much bigger than walnuts, these tiny birds forage from dawn to dusk and survive the winter eating insects. HarperCollins hide caption

Enlarge image.
itoggle caption HarperCollins

After years of trying to figure out where kinglets went at night, Heinrich spotted these four birds, which look like one ball of fluff, huddled together on a branch. Bernd Heinrich hide caption

Hear a kinglet's call.
itoggle caption Bernd Heinrich
Jacket cover of Winter World: The Ingenuity of Animal Survival

In his new book, Heinrich reveals the ingenious tactics animals in his local woods use to survive the harsh realities of winter. HarperCollins hide caption

itoggle caption HarperCollins
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University of Vermont biology professor Bernd Heinrich has always been fascinated by nature. From the age of 10 he grew up in Maine, spending his time exploring the wilderness and collecting insects, birds and other creatures.

The researcher, author and nature illustrator has written numerous books on the natural world. When he's not at work in Vermont, he spends his time in the forests of Weld, Maine. There, he has built by hand a log cabin that serves as the base camp for his research into the wildlife that populates the nearby woods.

At the moment, he's fascinated with how northern creatures survive the winter. In January, Heinrich published a book on his observations entitled Winter World: The Ingenuity of Animal Survival. Recently, NPR's Andrea de Leon spent the day with Heinrich exploring the secret lives led by animals in winter.

Trekking through the woods in temperatures well below freezing, Heinrich points out many subtle signs of wildlife activity that would go unnoticed by the untrained eye. In a thicket of tree branches, he stops at what appears to be a mass of cobwebs. Inside are tent caterpillar larvae, waiting out the winter. He explains that these creatures make their own glycerol — otherwise known as anti-freeze — to survive the cold climes.

Tiny stacks of pine cones and apples, he reveals, are probably the secret stash of an unseen tree squirrel. A disorderly pile of twigs turns out to be a raven's nest. Wing imprints barely visible in the snow suggest the bird's landing site. That's Heinrich's doing: he likes to leave carcasses out near his cabin to draw the ravens close.

"I like to have them around," Heinrich says. "I know the pair over there [in the nest] and so I want to make sure they have something to eat. I think right now it might be kind of hard for them."

The snow, Heinrich explains, isn't deep enough to trap the deer anywhere. That means deer aren't dying of starvation — and therefore, no carcasses to provide food for the ravens.

It's this kind of attention to the tiniest details that makes Heinrich such a keen observer of the natural world. Among his recent discoveries: Red squirrels bite hundreds of tiny holes in maple trees, holes they remember and return to when the sap begins to flow.

One of Heinrich's favorite animals to ponder is the Golden-crowned kinglet. Kinglets, he explains, are in flagrant violation of what's known as Bergman's Rule, which states that northern animals are larger because they need big bodies to conserve heat. But kinglets are miniscule, weighing about as much as two pennies. They forage from dawn to dusk without stopping and survive the winter eating insects. And at dark, they seem to vanish.

"They're so small and their coloration blends with the foliage, so you don't really see them except through movement," Heinrich explains. "A lot of time they will hover in front of branches like a hummingbird."

A few weeks ago, after years of trying to figure out where kinglets disappeared to, Heinrich spotted four of the birds huddled together on a branch for the night. In his photograph, they look like a single ball of fluff, tiny tails protruding in different directions.

It's the kind of discovery that keeps Bernd Heinrich going back to the woods, his head full of ever more questions.

"I'm still trying to see something new all the time," Heinrich says. "So I would say that what a good day is, is seeing something that I hadn't seen before."

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