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1 December 2004 Clear-eyed observation of wild, unrestrained animals
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Winter World: The Ingenuity of Animal Survival. Bernd Heinrich. HarperCollins, Ecco, New York. 2003. 368 pp., illus. $24.95 (ISBN 0060197447 cloth), $14.95 paper (ISBN 0060957379 paper).

Bernd Heinrich, an emeritus professor of zoology at the University of Vermont, applied his understanding of animal physiology and behavior to meet the challenges of the North American 100-Kilometer Championship race in Chicago and become the ultramarathon champ, as he wrote in Racing the Antelope. His superb books—15 to date—also garner medals: the L. L Winship/PEN New England Award, the Rutstrom Authorship Award for Conservation and Environmental Writing, the New England Booksellers' Award, and the John Burroughs Medal for Natural History. Heinrich's Bumblebee Economics was nominated for the National Book Award in science.

In his latest book, Winter World: The Ingenuity of Animal Survival, Heinrich explores the strategies that enable animals to survive icy days and numbing nights in their natural habitat. Through clear-eyed observation of wild, unrestrained animals, complemented by his own ingenious experiments, Heinrich unravels the evolutionary innovations that allow diverse species such as butterflies and bats, flying squirrels and frogs, kinglets and caterpillars, and many others to endure such extreme climatic conditions, within behavioral and physiological constraints. His explanation of the physiological ecology of winter adaptation will delight and inform scientists and naturalists.

Winter World opens with a brief chapter on definitions and terms that relate to activity and body temperature. The 24 chapters that follow focus on the diversity of mammals, birds, reptiles, amphibians, and insects living in the forest beyond Heinrich's homemade log cabin—and sometimes inside the cabin—in western Maine. He supplements his own field observations with the research findings of other scientists to amplify our understanding that in the northern woods heat means life, but cold does not necessarily spell death.

Where do northern animals dwell in winter if they cannot migrate south, as certain of our own species do? How does a 5-gram golden-crowned kinglet cope on nights with a chill factor near −50° Celsius (C)? When does being fat translate into being fit? Adaptations to winter are as diverse as the species Heinrich describes.

For example, the star-nosed mole digs in for the winter below the frost line. When snow insulates the ground, moles can hunt for winter food closer to the surface because the subnivian space (the zone above the soil and below the snow) usually remains close to 0°C. The name of the game is warmth and fuel.

Heinrich guides us into the woods to unfold the mystery of how the kinglet nests successfully in late winter. A kinglet hangs its cup-shaped nest like a hammock, within spruce or fir twigs that shield the birds from wet and cold. The nest is lined with lichen, moss, strips of paper birch, and caterpillar silk, and insulated with feathers and snowshoe hares' downy fur. Feather counts of 2486, 2674, and 2672 in three individual nests attest to the coziness of these small shelters—thus the kinglet supplements its own feathery insulation by creating a favorable microclimate. Moreover, Heinrich observes that kinglets forage nonstop all day, explaining how a kinglet, weighing no more than two pennies, can find sufficient daily fuel, up to three times its body weight. A kinglet's gut contents reveal the bird's winter energy source: inchworm (geometrid moth) caterpillars. Caterpillars in winter? Whack a tree; caterpillars shower down. Do kinglets overnight with adequate fat reserves? Probably not, posing an unanswered question of just how cold a kinglet becomes in severe winter. Perhaps it goes into overnight mini-hibernation, like a hummingbird.

Torpid turtles pile up in a communal hibernaculum (Graham et al. 2000). Map turtles and softshell turtles congregate from November through March, stretched out on the river bottom. Inactive, not even breathing, turtles most likely take up sufficient oxygen from the 0.1°C water (Graham et al. 2000).

Amphibians evolved diverse winter strategies in different habitats. Heinrich finds toads when he turns garden soil in the autumn; the Manitoba toad (Bufo hemiophrys) hibernates in gopher mounds (Tester and Breckenridge 1964). The wood frog hibernates beneath leaves, and the winter habitats of spring peepers, gray tree frogs, and chorus frogs await discovery. All four frog species pack their cells with glucose that serves as antifreeze. Ice in intercellular spaces crystallizes on protein. Breathing halts. Hearts stop. Metabolism plummets until spring.

What animals get fat to be fit (to paraphrase a line from Racing the Antelope)? The skunk, jumping mouse, black bear, woodchuck, and raccoon plump up when the food supply dips in autumn; their body is their fuel tank. In contrast, an obese flying squirrel lugging excess fat in flight would be at a disadvantage. The flying squirrel remains active in winter—it does not hibernate, store food, or fatten. To investigate how well the nest of a flying squirrel insulates, Heinrich heated a potato to 60°C. Within the nest the potato cooled to 42°C in 35 minutes; outside it cooled to 15°C in −13°C air. Flying squirrels also cuddle in groups Heinrich has counted as many as 10 flying squirrels leaving a tree hollow. Glaucomys volans, the southern flying squirrel, appears to form even more impressive winter aggregations—up to 50 individuals (Weigl et al. 1999).

The author's graceful black-and-white sketches evoke the nature of winter beautifully—for example, a grouse tunneling deep under the snow and a flying squirrel peeping from a maple. Readers inspired to learn more about winter adaptations will appreciate that the references are sorted by chapter. Many readers will wish to dip into Winter World repeatedly, but an index is lacking, a blemish that the publisher could have remedied.

Heinrich credits a nature guide published in 1922 (Hans Wagner's Taschenbuch der Käfer [Pocketbook of Beetles]) as the first book he read that linked the contents of paper pages with something concrete in nature (Cannon 1999). Winter World provides readers a similar link between the book and the natural world. Although not produced as a textbook, Winter World might serve as an undergraduate supplemental text for a course in animal ecology, evolutionary biology, or vertebrate physiology. For a course in science writing, it would serve well as a source of well-crafted writing. Winter World's audience will range from those who venture out only to a city park to those who, like Heinrich, climb an 80-foot-tall spruce to see life from a treetop perspective.

Swallows migrated to the moon, asserted naturalist John Morton in the late 18th century. Heinrich's splendid book gives us a more informed view of animals' adaptations, in this case, the adaptations that enable survival in winter. It is the rare book that teaches us to see more clearly even as it delights us. Winter World will impel you to take a walk in the winter woods.

References cited


W. J. Cannon ed. 1999. Forced to choose. American Scientist 87:6545–552. Google Scholar


T. E. Graham, C. B. Graham, C. E. Crocker, and G. R. Ultsch . 2000. Dispersal from and fidelity to a hibernaculum in a northern Vermont population of common map turtles, Graptemys geographica. Canadian Field Naturalist 114:405–408. Google Scholar


J. R. Tester and W. J. Breckenridge . 1964. Winter behavior patterns of the Manitoba toad, Bufo hemiophrys, in northwestern Minnesota. Annales Academiae Scientiarum Fennicae, A IV (Biology) 71:424–431. Google Scholar


P. D. Weigl, T. W. Knowles, and A. C. Boynton . 1999. The Distribution and Ecology of the Northern Flying Squirrel, Glaucomys sabrinus coloratus, in the Southern Appalachians. Raleigh (NC): North Carolina Wildlife Resources Commission. Google Scholar


KARLENE SCHWARTZ "Clear-eyed observation of wild, unrestrained animals," BioScience 54(12), 1151-1153, (1 December 2004).[1151:COOWUA]2.0.CO;2
Published: 1 December 2004
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