I’m guessing lots of us who love nature have wondered the same thing in the last few weeks. “As the temperature drops below zero, how do those small birds with bare feet survive out there?”
Well, it turns out that although our avian winter neighbors share a similar technique for keeping their feet from freezing, their strategies for dealing with cold, snowy days can differ.
First Rule: Use Those Feathers!
We humans love down jackets on cold winter days and snuggle beneath down comforters on winter nights. Well, birds like the female Northern Cardinal (Cardinalis cardinalis) above, or the Tufted Titmouse (Baeolophus bicolor) pictured at the top of the blog, use the same technique. When birds fluff up their feathers in the cold, they trap a layer of air between the feathers. Their body temperature – in small birds more than 100˚ F – warms the air layer just as it does in our jackets. According to Peter Marra, head of the Smithsonian Migratory Bird Center at the National Zoo, “Birds’ feathers provide remarkable insulation against the cold, and the oil that coats feathers also provides waterproofing, which is important since the only thing worse than being cold, is being cold and wet.” Here are a few of birds making the most of their feathers on a recent cold morning. (Click on photos to enlarge; hover cursor for captions.)
What About Those Bare Feet, Though?
Last summer I caught this American Goldfinch (Spinus tristis) staring at its feet in a tree near Lost Lake. I laughed to think that perhaps it was worrying about how they’d feel on a snowy day! Birds really do have very cold feet in the winter. According to scientist and professor Bernd Heinrich on the Cornell website, the feet of chickadees stay just above freezing even while their body temperatures are very high. Presumably, they don’t feel it much. Their feet are mostly tendons and bones with very few muscles or nerves. If you look at those three birds with feather puffed that are pictured above, you can see they’ve hunched over their feet, covering them with their body feathers. Or sometimes birds simply tuck one leg at a time against their breast. Also, the arteries and veins in birds’ feet are close together. As Heinrich explains it, a bird’s feet are provided with continuous blood flow which keeps them from freezing. Since the arteries pass close to the veins in a bird’s legs, the cooled blood from the feet gets warmed on the way back to the heart to keep the bird’s body warm. And the warm blood from the heart is cooled down as it moves out to the legs, reducing heat loss. Pretty efficient system!
Second Rule: Eat as Much as Possible!
On cold days, small birds really need to stuff themselves every few minutes to keep warm. When you see a White-breasted Nuthatch (Sitta carolinensis) or Black-capped Chickadee (Poecile atricapillus) dashing from your feeder to nearby trees, it’s eating some seeds and storing others in the trees’ bark. Amazingly, the brains of Chickadees expand in the fall to improve their memory so that they can later find those seeds or nuts. According to Cornell’s Birdsleuth website, “neurons are added to the Chickadee’s hippocampus in the fall, increasing its volume by about 30%.” As a result, Chickadees can remember up to a thousand places in which they’ve tucked their winter provisions! (I’m sure I’ve mentioned this before in the blog, but it’s so amazing that it bears repeating!)
But What Do They Eat in Winter?
Mourning Doves (Zenaida macroura) and American Goldfinches can be gluttonous at feeders during the winter because they are vegetarians; no insects or caterpillars for them! On most winter days, they can find seeds or fruits, but your feeder helps to supplement the wild supply. Mourning Doves can eat 12-20% of their body weight per day! They store seed in their crops, a muscular pouch near the throat, and digest it later to help keep themselves warm at night.
I’ve seen Cedar Waxwings (Bombycillia cedrorum) eating frozen vine fruits or leaf buds that overwinter on the branches of trees.
But many local birds, including Waxwings, are omnivores who can eat a wide range of foods. The Tufted Titmouse, White-Breasted Nuthatch, Chickadees and all kinds of Woodpeckers (family Picidae) spend winter days probing loose bark or hopping along branches looking for frozen dinners; insects, insect eggs, pupae or perhaps a frozen caterpillar will do just fine as sources of protein on a cold day.
American Crows (Corvus brachyrhynchos), being bigger birds, will eat almost anything to “stoke their furnaces” during the winter. In our area, the carcasses of White-Tailed Deer (Odocoileus virginianus) provide lots of good protein. And if a crow finds one, it notifies its family and friends to join the feast. (No fair being squeamish. We all have to eat!)
Where Do Birds Spend Cold Winter Nights?
According to the Smithsonian’s Peter Marra, “Many small birds, like Black-Capped Chickadees, Eastern Bluebirds, and House Wrens, will gather in large groups at night and crowd together in a small, tight space to share body heat.” Sharing body heat keeps down fat loss during the night to preserve energy for the next day’s foraging. In his article for Cornell’s All About Birds, Bernd Heinrich describes finding a group of tiny Golden- Crowned Kinglets (Regulus satrapa) huddled in a circle on the branch of a pine tree, beaks in, tails out, sharing their body heat on a winter night. These tiny birds, which overwinter in our area, are about half the weight of a Chickadee! This lovely winter photo of a Golden-crowned Kinglet was taken by a photographer named cedimaria at the website inaturalist.org.
Bernd Heinrich reports in his essay collection, Winter’s World, that woodpeckers provide some cozy winter housing for other birds as well as themselves. Every spring, woodpeckers make a fresh hole for raising their young, but they tend to use them for only one year. So small birds can often find an abandoned woodpecker hole to get out of the wind and snow on a winter night. In the autumn, Dr. Heinrich has also spotted both Downy Woodpeckers (Dryobates pubescens) and Hairy Woodpeckers (Dryobates villosus) constructing special overnight shelters just for winter use. I spotted a Downy doing just that in Gallagher Creek Park one November day. Note the flying wood chips!
Special Winter Strategies Can Be Helpful…
Even though Chickadees can excavate their own holes, in extreme cold they require a few extra tricks at night. According to the Audubon society, these little birds can lower their body temperature at night by as much as 22 degrees, minimizing the difference between their body temperature and the bitterly cold air. They also keep warmer by shivering, which activates opposing muscle groups and produces heat. Luckily, they can even shiver while sleeping, which is something I can’t quite imagine doing! And of course once settled, like many birds, they can tuck their beaks and feet into their feathers to preserve heat as well.
Though they don’t appear in our parks these days, Ruffed Grouse (Bonasa umbellus) survive days of light fluffy snow in a surprising way. They burrow into the snow, creating a long tunnel with a chamber on the end. These one-day burrows not only provide insulation, according to Bernd Heinrich, but they also provide protection from predators. Large dark birds are very visible against the snow! (This photo was generously shared at iNaturalist.org by photographer Brian Murphy.)
Thank Goodness for Our Adaptable Winter Birds!
Aren’t you glad that some birds stay with us all winter? And that some actually arrive for an extended stay just as the snow begins to fall? The constant flutter of a busy Chickadee, the “yank yank” call of a Nuthatch as it circles a branch or the friendly chirping of a flock of foraging Tree Sparrows in dry grass are so companionable on gray winter days. And what could be more heartening on a frigid morning than the sight of scarlet Northern Cardinals or azure Blue Jays in a snowy bush? I’m so thankful that some birds have figured out how to survive the cold along with us. By taking shelter, shivering, eating heartily, and snuggling into down comforters very much like we do, they keep us company as we make our way towards spring.
Footnote: My sources for information, besides Oakland Township’s Stewardship Manager Ben VanderWeide, are as follows: Allaboutbirds.org, the website of the Cornell Lab of Ornithology at Cornell University; Wikipedia; A Field Guide to Nature in Winter by Donald Stokes, Winter World by Bernd Heinrich, A Naturalist at Large by Bernd Heinrich and others as cited in the text.