Handouts Fuel Songbird Survival

Every year as winter approaches and our thoughts turn to wool blankets and nights around the wood stove, I begin to hear the same questions asked about birds:

How do birds stay warm in the winter? Do their feet get frost-bitten? Can birds survive in sub-zero temperatures? How can I help birds survive frigid weather?

Birds, like humans, are warm-blooded. Birds maintain a constant body temperature by metabolizing or burning food “fuel.” Heat is supplied and regulated throughout the body by the circulatory system.

The normal body temperature of humans is 98.6, but birds maintain higher body temperatures - from about 103 degrees for large birds like grebes, to about 112 degrees for song sparrows.

Perching, or song birds, have higher body temperatures than larger birds like geese and swans, and are therefore more endangered by freezing conditions because higher temperatures are more difficult to maintain.

Humans might be in big trouble by a plunge, or rise in body temperature by even a few degrees, but songbirds are more flexible. For example, black-capped chickadees can enter a state of regulated hypothermia, plunging body temperature to conserve energy overnight.

Typically, chickadees can drop their nighttime body temperatures by 10-12 degrees lower than their normal daytime temperatures.

In a sense, birds simply damper down the flue and let the wood stove simmer overnight. If the birds have judged it right, there are still coals in the morning to get another fire going with added fuel. This ability helps birds to make it through long winter nights when they might have to go more than 12 hours without food.

Twelve hours without a meal doesn’t sound like that big a deal to humans, but many birds reach a critical stage after only fifteen hours.

Studies show birds that feed by day can survive only about 15 hours without food when the temperature is 5 degrees. The length of survival dips with every drop in degree below that temperature.

Consider the bird that has gone 15 hours without food, and then is greeted at daylight with a snow storm that lasts into the afternoon. The bird could be doomed.

It is critical to provide a variety of high-energy foods in our yards for birds during the winter. Availability of a reliable food source may mean survival for bird species such as chickadees, kinglets, and other songbirds.

Frigid temperatures are particularly hard on golden-crowned kinglets. Evening grosbeaks and members of the finch family have well-developed crops, allowing them to store large amounts of seeds that may be metabolized overnight.

Redpolls, known to survive colder temperatures than any other bird species, have a similar storage pouch in the esophagus. Redpolls choose high energy foods to cram into the pouch before nightfall. This “warm”, mixture aids in maintaining a higher metabolic rate, helping them to cope with below-freezing conditions.

Bluebird boxes and other nesting boxes, along with natural tree cavities, also play a critical role in the winter survival of many songbirds. Chickadees - on occasion - and kinglets, nuthatches, and woodpeckers, may crowd together in a nest box, or tree cavity, to conserve body heat on frigid nights.

Studies show that the combined body warmth of three or more birds roosting together in a cavity, may help to reduce heat losses by as much as 37 percent.

One researcher found more than a dozen bluebirds huddled together in a nest box! If you take down bluebird boxes for cleaning and repair in the fall, be sure to put them up again for winter-roosting songbirds.

Birds can endure cold weather because heat losses from their bodies are lessened by a coat of feathers. We have all seen birds “puffed up” in the winter, an ability that helps to insulate their bodies with confined air trapped beneath the feathers.

Birds also have few fleshy parts such as ears or a nose exposed to the air. This prevents heat from wicking away as it does on humans and many mammals.

A bird’s bill is made of horn, not skin, and therefore gives up little heat. We have all seen perching birds tuck one leg underneath the feathers on their bellies. This behavior also helps to conserve body heat.

Shivering is a valuable tool to help adjust body temperature in birds, as well as in mammals. It’s the primary way for a bird to stay warm while at rest. However, shivering costs energy, which must soon be replenished.

Severe cold can exact a toll upon songbirds during the winter. We can help by providing sunflower seeds and suet, peanut butter and cornmeal, and other high energy foods.

We can make sure feeders are full at those critical hours in the morning and evening. We can provide nest or roost boxes, to help protect resident birds from the elements during periods of extreme cold.

And don’t forget to provide a water source that won’t freeze. Pet bowl or stock tank heaters work well.

Illustration by Maurice Vial