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Dec 4, 2017 2:12 PMPublication: The East Hampton Press & The Southampton Press

Adapting To Winter

Great blue herons have a hard time fishing on ice-covered ponds. MIKE BOTTINI
Dec 5, 2017 9:37 AM

In a previous column, I discussed two general strategies employed by our native wildlife to deal with the stresses of the winter season: migrating to a less stressful and energy-demanding environment, and hibernating or greatly reducing energy requirements by entering one of several states of inactivity.What about the animals that remain active here on Long Island throughout the winter season? There are quite a few interesting tricks they’ve developed to deal with cold temperatures and changes in their food supply.

One of the most obvious adaptations to winter is found among the furbearers: molting and exchanging a light-weight summer coat of fur for one that is more dense and has a higher insulation value. This is most obvious among our white-tailed deer—who replace their bright, reddish-brown summer fur with a dull, gray-brown coat—and the red fox, whose summer and winter coat colors are similar but the latter has noticeably longer hairs.

I find it interesting that a similar strategy is apparently not employed by birds. Their molts have evolved to replace worn out feathers and, among adults, breeding plumage with non-breeding plumage and vice versa. Beneath the outermost feathers, called contour feathers, are small, downy feathers that are very efficient at trapping air. By “fluffing up” the contour feathers, a process called piloerection, more space is created for the downy feathers to trap air. Warmed by the underlying skin, this trapped air is very efficient in keeping birds warm on cold winter days.

What about the unfeathered, bare skin found on bird’s feet and legs? The challenge this creates is most noticeable among the web-footed ducks, geese and swans standing on ice-covered ponds, and is dealt with by way of an ingenious counter current heat exchange in their circulatory system.

Warm, oxygenated, arterial blood leaving the feathered portion of the leg and heading toward the feet is shunted into a network of tiny blood vessels that engulf the much cooler veins exiting the feet and carrying carbon dioxide and other cellular waste products. Warmth from the arterial blood is conducted into the veins, resulting in a significant drop in the temperature of the arterial blood as it continues farther down the leg, and a significant rise in the temp of the venal blood as it heads up the leg and into the bird’s warm core. This heat transfer is so efficient that the core temperature of the bird is approximately 100°F while the feet may be a degree or two above freezing, with a temperature differential of 65 degrees!

Many waterfowl and seabirds arrive here in December from points north to take advantage of our relatively mild winters, ice-free waters, and abundant marine prey: fish, shellfish and crabs. Among this lot are the loons, scoters, eiders, and mergansers. However, many songbirds that overwinter here must shift their diets from a mix of insects, arthropods and fruits to a strictly vegetarian diet of fruit and seeds. This includes the large flocks of American robins found here and throughout the New England area during the winter. Wild turkeys also make this shift, scratching the forest floor for acorns and beechnuts, and feeding on the buds of small shrubs and saplings.

How our great blue herons manage here in winter is a mystery to me. This wading bird stalks the shallow edges of ponds, creeks and marshes for fish and crabs, and the latter prey have usually migrated to deeper water or buried themselves out of sight in bottom sediments for the winter. Yet we record more great blue herons here in winter than any season of the year.

Among our herbaceous mammals, deer and cottontail rabbits shift from a diet of succulent vegetation to woody browse, and muskrats shift from aquatic greens to tubers. Deer also rely heavily on mast (acorns, beechnuts and hickory nuts) not only to put on a layer of fat in the fall but to feed on throughout the winter. Deep snow cover requires extra energy to scrape through with their hooves, and that work doesn’t always reveal any of the seeds and nuts.

Gray squirrels bury acorns in the snow-free ground during the fall months, and mark their locations with scent. Flying squirrels, chipmunks, mice and voles will also cache seeds and nuts for winter use. Snow cover is an advantage to the latter three, as it insulates their underground dens and burrows.

Mice and flying squirrels are not adverse to moving indoors for the winter and relying on your home heating equipment to keep them warm. They will also huddle together for warmth during extreme cold, up to two dozen in the case of the flying squirrels. This is also a strategy employed by some birds, such as kinglets, winter wrens, sparrows, chickadees and bluebirds. One reference cites 46 winter wrens huddled together in a nesting box on a cold night!

Some birds also save energy in winter by allowing their body temperature to drop, from as little as 5 to 7 degrees in the case of red-tailed hawks when food is scarce, to as much as 22 degrees among chickadees, inducing a form of torpor or regulated hypothermia ... amazing!

Shrews and moles expand their network of tunnels deeper into the soil not only for warmth, but to follow their favorite prey that has moved down well below the frostline: earthworms and other arthropods and insects.

Raccoons, skunks and opossums are active during our winter, to varying degrees, with all three laying in their respective dens and sleeping through the cold snaps, not unlike a couch potato.

Meanwhile, huddling, laying-in and sleeping through cold snaps are not options for members of the hyperactive weasel family—otter, mink and long-tailed weasel—and the red fox and gray fox. They must keep their internal furnaces stoked with food to keep warm, and that means being on the move. By the end of a particularly harsh winter in New England, the red fox might lose 40 percent of its body weight.

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