Man, it’s cold. Bone-chilling, mind-numbing cold. But you wouldn’t know it by the bird behavior at the feeder, deer in the backyard, and waterfowl lazily loafing the day away on Lake Michigan. Funny how sportsmen — tough while hunting and fishing — are thankful for season closures and the end to cursed wader leaks and mild hypothermia. Animals, however, are in it 24/7, without a whisper of complaint.
For some reason, fur-bearers appear more able to deal with unforgiving Mother Nature. Maybe it’s the fuzzy coat, but it makes sense just looking at them. Properly equipped, they thrive in all but the most brutal winters. But how birds deal with it daily is fascinating. Their delicate nature, fluffy feathers and light body weight suggest they’ll topple over in a stiff, cold breeze.
Driving along beautiful M-22, I’m always on the lookout for ducks and geese. A regular pack of Canadas and mallards congregated among ice floes courtesy of a sudden temperature plummet. They looked content; if I had wings, I’d have been in Florida. With a light snowpack, food in a nearby picked cornfield was available, enough to keep their little internal engines running; prior to and after feeding, they spend the day on the bay, where the water temps are what, 33 degrees? How in the world do they do it? Thankfully, my (ancient) college degree says I can once again bore you witless about the incredible technology of our fine feathered friends.
Birds maintain a high body temperature compared with most animals — 40 degrees Celsius. High body temperatures allows for high rates of physiological processes, aiding in such important factors as quick reflexes and enduring flight that is strong and active. But increased metabolism produces — releases — heat. Luckily, birds control heat loss in several ways.
Over the course of a 24-hour day, avian body temperatures fluctuate a couple of degrees (humans do that and can’t get out of bed for three days!). But during cold winter nights, some birds, such as the chickadee, will drop 10 to 12 degrees. Others, like hummingbirds, will drop their nighttime body temps as much as 30 degrees or more, falling into “torpor,” a hypothermic state associated with drastically low oxygen consumption.
And lower O2 consumption means less heat is lost through the body. The lower the temperature drop, the longer it takes them to come out of it, though, which may explain why I hear my chickadees peeping for a while before coming to breakfast. This phenomenon must exist in young humans, as well — my teenage kids are in a state of torpor every morning before school.
Another interesting adaptation is their ability to alter blood flow to their skin and extremities, as well as tuck a leg or bill into their feathers, shifting exposure to the elements. They also go through a process called acclimatization, a natural physical adjustment to temperature changes. As daylight shortens and temperatures drop in the fall, birds increase stores of lipids (fats) and carbohydrates to combat a potential lack of food in the future or to prepare for migration. Game species, such as woodcock increasing their diet of earthworms, or mallards gorging on corn, come to mind.
My favorite, though, is their coat — the feathers. A hollow “calamus” extends from the skin and becomes the “rachis,” or central shaft of the feather. Off the rachis extend branches, called “barbs,” with tiny “barbules” that link each barb together to create a flexible but protective surface. The barbs and barbules at the base of the rachis — closest to the skin — are a fluffy and thin “plumulaceous” (the “u’s” are long) texture, or down. On some birds, like ruffed grouse, an “afterfeather” protrudes out from the base of the rachis, and is almost always downy in nature, as well as long for birds in cold climates. This plumulaceous nature of feathers provides insulation.
Ducks and geese are covered in definitive down, a downy mixture of barbs and barbules that extend off the calamus and loosely tangle with each other, trapping air, and creating another layer of insulation.
“Pterylae” are densely concentrated feathers grouped in “feather tracts.” In these tracts, tiny muscles are linked throughout the bases of the feathers, allowing birds to control their feather position for insulation, like a mallard puffing up on a cold winter morning or turkey displaying in the spring. Several pterylae are spread throughout a bird’s body, separated by areas with little or no feathers, called “apteria.” These open areas are perfect for warming a tucked bill or foot; their version of a pocket.
Feathers need continual maintenance, like removing salt and dirt from a car, so birds spend a lot of time “preening.” They’ll run their bills along flight feathers, much the same way you’d do with your hands, to straighten out any gaps caused by flight and connecting the barbs and barbules once again. While preening, birds will also add a waxy coating to their feathers by dipping their bills in the “uropygial gland,” at the base of the tail. This “preen gland” secretes a combination of oils, waxes, and fats to help clean feathers and keep them moist and less brittle, preventing cracking. Waterfowl have an especially large preen gland, and with regular applications, keep the feathers waterproof and insulated, not to mention more buoyant.
These are but a few of the physiological adaptations that help birds survive our harsh winters. Whether you're observing a dozen mallards puffed up on an ice shelf or being greeted by a chorus of tiny bird calls, a deeper understanding of the animal world only enhances the overall experience.