Winter poses several challenges for our birds, especially when the temperatures drop below freezing. We do not often think about or wonder how our birds survive the colds nights, we just know they do or at least we hope they do. Even those moments in the deep South, Desert regions or the Pacific coast where a cold snap or multiple inches or feet of snow fall, can effect a bird population. Winter brings extreme cold temperature, strong winds, driving snow and rain.
Nights seem to last forever. 16 hours of darkness and in some locations more. That does not leave a whole lot of time to forage and feed. Yet, many birds must at least triple their normal intake to survive and do it in half the time. Each winter we lose many of our feathered friends to the rigors of winter. It's how "Nature" works. Survival of the fittest, Passing on the strongest genes.
Birds have many adaptations to survive the extremes of winter. Some birds migrate, some adjust their diet habits. Birds such as chickadees and American goldfinchs add feathers in preparation for winter. The typical chickadee or goldfinch is covered with about 1,000 feathers during the summer. By the time winter arrives, they have doubled that count to more than 2,000 feathers. For a small bird, that can be some serious added bulk and weight.
During cold, windy or just a plain nasty day, birds will fluff up their feathers. By doing this, they create dead air pockets, much like insulation or a double pain window. This reduces the heat loss by up to 30%. Extra feathers and fluffing is not enough to make it through a cold winter day yet alone the cold, long dark nights.
Birds also have a unique circulatory system in there legs to help them cope with cold temperatures.
Pay attention now.
Warm arterial blood from the birds interior, which is on its way to the bird's legs and feet, passes through a network of small passes that runs along the cold returning blood veins from the feet. The network of vessels acts like a radiator and exchangers the heat from the out-going warm arterial blood to the cold venous blood. By warming up the old blood, no heat is lost and the feet receive a constant supply of life sustaining blood. This is also why water fowl can swim in near freezing water and not get cold.
Fat is another important winter weather survival adaption. Fat acts as an insulator in addition to an energy reserve. During the day, birds eat to build up fat reserves. On average, a bird can put on up to 15% to 20% of body weight in fat before it becomes to heavy to fly.
Now remember, days are worse and cold. Birds have to eat enough to survive the day as well as replenish the fat reserves. The smaller he bird, the higher the metabolism (more energy burned). Birds do not have brown fat, the kind we have, instead they have white fat. White fat is a high-energy fuel used to power the bird's warming process.
Thermogenesis is a fancy name for shivering. You can not really see it, but all birds shiver in the cold of winter. From the largest of birds like eagles and water fowl to the smallest of birds like hummingbirds. They all shiver to maintain their core body temperature at about 106 to 109 degrees, depending on the species.
Shivering produces heat five times their normal basel rate and can maintain a normal body temperature for six to eight hours at temperatures dropping to minus 70 degrees Fahrenheit. Without shivering the bird's body temperature would quickly drop and the bird would become hypothermic.
At night, birds such as the little chickadee take shivering, or lack of one step further. To conserve heat and energy, chickadees can lower their body temperature by interrupting their shivering. These periods of activity allow the bird's body temperature to slowly cool, until it drops about 10 or 12 degrees. At this point, the bird enters a state of unconsciousness called torpor. Respiration and heart rate will also drop during this period.
As morning nears, the periods of activity decrease until the bird is constantly shivering once again. The body temperature is back in the normal range and the bird regains consciousness. The results of this torpid state is an energy savings of up to 20% during a typical winter night.
Conserving energy is very important when you consider how little fat a bird can store. Based on a daily increase of body fat of 15% a typical chickadee has about 16 to 24 hours of fat or energy reserves to carry it through a winter night. That my friend is why it is imperative that a bird gets out early in the morning and stays out late to find food regardless of the weather.
If it does not replenish its fat reserves every day, the bird will not have enough energy to make it through the next night and will die. There was a time when the natural world provided food for most wildlife. With the constant shrinking of habitat, winter protection and food supplies continue to shrink.
You can increase the odds for birds and some mammals by simply filling your feeders with their favorite food and offering suet. Fresh water is important as well. When birds are required to eat icy cold snow, it takes valuable energy to warm that snow as it passes through.
Next time you trudge out into the cold or even the warmth to fill your feeders, think of this, "Nature" has provided birds with some wonderful tools to survive, whether it is migration, blood circulation, change of diet, added feathers, or shivering.
Birds are truly a wonder for us to enjoy. In one way, it is unfortunate that many birds now need our help to survive. Yet, look at the education and joy we get out of caring and feeding our birds.