I’ve been hearing a lot of complaints from people who are feeling lonely this winter. For once, they aren’t feeling cooped up by icy roads and constant blizzards. Instead, we miss our feathered friends! A suite of factors, including the nice weather, means that birds are not as abundant as usual at our backyard feeders.
My guess is that with shallow snow many birds are able to find food in the woods. Plus, the mild temperatures reduce the number of calories they require to stay warm. In addition, the grosbeaks, redpolls, and crossbills we love to see are “irruptive species.” To irrupt means to enter an area suddenly (in contrast to the lava erupting out of the volcano suddenly). We don’t see these irruptive species every winter, at least not in any quantity. Most migrations are driven by food availability, and these are no different. This year, their favorite foods are more abundant elsewhere.
One exception, at least at my feeders, are pine siskins. These stripey little finches with yellow highlights breed in the remote forests of Canada, as well as northern Wisconsin and Minnesota. When their typical winter food supplies in the north are low, pine siskins may flock into New England, the upper Midwest, or even the southeastern United States. They are looking for plentiful supplies of seeds from pines, cedars, larch, hemlock, spruce, alder, birch, and maple. I’m not sure what natural food is abundant this year, but my plentiful pine siskins seem to be enjoying a “sunflower chips” mix that has some hulled and some whole sunflower seeds.
In fact, I’ve been observing that pine siskins are the most dominant birds at my feeder. They will hiss and spread their wings aggressively to prevent goldfinches, chickadees, and nuthatches from swooping in to grab one of those tasty sunflower seeds.
By eating all those seeds, pine siskins put on 50 percent more winter fat than their cousins—common redpolls and American goldfinches. Little birds don’t store fat in an insulating layer of blubber like penguins and whales; they accumulate stores of brown fat around their wishbone and abdomen as a ready source of fuel for their metabolisms. Siskins also store a bedtime snack right in their esophagus—in the expandable section called the “crop.” But it isn’t just a single cookie and glass of milk; their crop can store seeds equal to 10 percent of their body mass.
Those calories could get them through five or six hours of sub-zero temperatures. They can survive negative 94 degree Fahrenheit nights by revving up their metabolic rate to five times normal for several hours. That’s 40% higher than other songbirds.
Why don’t more little birds put on that much fat for winter? Getting too fat can make it harder and more energetically costly to fly, and reduce their ability to escape predators. Chickadees may only achieve 10 percent body fat in the winter. Instead, chickadees store food. They cache up to 100,000 food items per year – most of them in the winter. In order to remember all of those caches, chickadees add new neurons for every hidden seed, berry, or insect. The result is a 30 percent increase in brain volume, which shrinks again during the easy-living days of summer.
Besides adding a little fat and a lot of neurons, chickadees grow 12 percent more feathers for winter insulation. That’s nothing compared to common redpolls, who add 31 percent more feathers! That’s a big increase for a bird that only weighs half an ounce to begin with. Why don’t more birds add that many feathers? During a Wild About Winter Ecology Workshop years ago, Prof. Sheldon Cooper from UW Oshkosh compared small birds adding feathers to putting a toddler in a snowsuit. A big being, like a snowy owl or an adult human, can still move pretty well, even if you add some puffy layers. The smaller the being, though, the more those layers can impede movement.
From fat to feathers, all winter adaptations have their pros and cons, just like this weirdly warm winter we’re having. If the birds have left you feeling lonely, take advantage of the clear roads and visit a human friend instead!
Author’s Note: Portions of this article are reprinted from 2014 and 2019.
Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.
For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our exhibit: “The Northwoods ROCKS!” is open through March 9. Our Winter/Spring Calendar of Events is ready for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.
Last Update: Feb 20, 2024 5:34 am CST
