(Editor's Note: This article was originally published on December 13, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
I tried to explain to my DG pal in Australia exactly HOW COLD it gets in North America during the winter. I recounted a story that I never get tired of telling. I have a friend from Chile who lives in Chicago. He tried to explain the winter cold to his mother, still in Santiago… "Open the freezer door and put your face in there. It's like that EVERY DAY!" How funny and true. Humans are able to acclimate to the climate and further adjust with help of shelter, clothing and often, warm drinks (mmmm cocoa). So how do our feathered friends keep warm in the winter and what can bird watchers do to help?
Birds that are not equipped for warm weather travel south for the winter; those that travel further south than Mexico are neotropical migrants. Birds that migrate mostly to find better food sources stay primarly north of Mexico and are considered continental migrants. Both continental migrants and non-migrating birds are equipped to handle cold weather with various physical adaptations.
Physical Adaptations to Keep Warm
A good pair of boots — While feet might be the first thing to get cold on a human body, birds are specially equipped to handle cold and ice. Beneath the thick, scaly skin of a bird fine webs of blood vessels are found. Artieries with warm blood sit closely to the veins and warm the colder blood in those veins before it returns to the body. This unique cirulating system helps keep the bird's feet stay warm.
Puffy down coats — Birds have the ultimate down coats. Semi-plume and downy feathers combine to trap air, keeping that insulating air at nearly 70º. By crouching at rest and roost, the bird uses its belly feathers to warm legs and feet. The beak and eyes, other unprotected body parts, also can be tucked under wings for warmth. Many birds often grow more feathers before winter. Body oils on feathers also help repel water.
Brrrrrr — Birds often employ shiver tactics (thermogenesis) to generate heat. This involuntary muscle contraction generates heat by expending energy.
Deep sleep — Birds experience a drop in body temperature, generally in the evening. This state of inactivity is called torpor and is designed to conserve energy. Many people see this during the day with hummingbirds that can be found clinging — upside-down — to feeders or branches. Unlike groundhogs and such, torpor in birds is short-term.
Behavioral Adaptations to Keep Warm
Saving for a rainy day (err, cold night) — In winter, birds benefit from a diet high in fat. In this way, they can eat all day and store energy for the night. Many birds like the Common Redpoll also have pouches in their throat for storing seeds. These birds fill their pouches to eat at a later time and location, often during the nighttime hours.
Let's cuddle — Like humans, birds find warmth with each other. Huddling together helps them stay warm. Many birds enjoy roosting boxes or will find protected areas to roost. Experts suggest cleaning out nest boxes to allow birds places to roost. There is some danger in this as birds on the bottom of the box may suffocate. Boxes designed specifically for roosting have entrance holes on the bottom and perching spots along ths sides.
Winter Needs for Birds
Landscape Plants — You can make a difference to your backyard birds for many winters to come by planning for their winter needs. Many plants are attractive choices for the landscape and offer birds seeds or fruit during winter months. Dave's Garden members from the Bird Watching forum (available to member and subscribers) compiled a list of best trees and shrubs for birds, along with lovely pictures of each. Consider planting some of these in your yard to feed your birds. If you live in an area that receives heavy snowfall, be sure you plant shrubs that grow above your average snowfall (generally two feet). Another tip is to leave seedheads through the winter. Ground-feeding birds will enjoy ornamental grass for seed and protection, while finches will feast on rudbeckia.
Food — When feeding birds provide high-fat and protein seeds like black oil sunflower seeds, safflower and nuts to name a few. Suet is another key feeding item in the winter. While some belive it is a myth, it is recommended to continue feeding birds throughout the winter once you have begun. This is especially important in populated areas where you may be the only feeding station nearby.
Water — It's easy to forget about water in the winter. While birds can eat snow, a fresh water supply is appreciated. Birds often bathe during the winter to keep feathers in top condition. Wild Birds Unlimited reports "Research has shown that a chickadee with well-maintained feathers can sustain a 70 degree layer of insulation between the outside air and its skin." There are a number of ways to provide unfrozen water for your birds.
Heated birdbaths are an exploding category on the market these days. You'll find many styles of baths including those that sit on a deck railing as well as ground versions with drip. Solar versions for milder climates are also available.
A cheaper alternative is a heated pet bowl. These can be found in pet and farm supply stores. Many of them are deep enough to add a small pump to act as a bubbler. If you choose this type, be sure to add some rock to provide a shallow area for access.Shelter — Protection from the elements and predators is found in both man- and nature-made forms. Evergreens in both tree and shrub form are ideal for such protection. After the holidays, many people leave their tree outside for the birds to use as protection. If you're feeling really ambitious, you could gather all the trees slated for recycling and put them in your yard! Brush piles are also important for birds in winter as are tall grasses. Birdhouses and roosts as described previously offer huddling areas for additional warmth.
Now is an excellent time to begin planning for next year's bird landscaping. Begin by selecting landscape plants suitable for your area and common winter birds. Investigate water options that best suit your environment. In helping birds combat the cold, you will be rewarded with endless entertainment all winter long.
Building Your Own Roostbox, Cornell Lab of Ornithology
What to Feed Backyard Birds, Marna Towne, Dave's Garden
Attracting Feathered Friends with Backyard Birdfeeders, Marna Towne, Dave's Garden
Best Trees and Shrubs for the Bird Garden (DG Bird Watching Thread)