January 10, 2011 (Big snow day in Atlanta)
Wow, lots of snow and lots of very hungry birds. Early this morning, I spread bird seed over the top of the frozen snow in my back yard. I did this as there were numerous ground feeding birds trying to find seeds under shrubs and other areas where the snow was not covered in ice. These ground feeding species rarely fly up to the typical hanging feeders or platform feeders that so many people use to feed our feathered friends. These ground feeding species include dark-eyed juncos, white-throated sparrows, song sparrows, chipping sparrows, Eastern towhees, fox sparrows and occasionally swamp sparrows and other sparrow species. I also made sure there was suet in my suet feeders for the woodpeckers, Carolina wrens, Eastern bluebirds and brown thrashers. During the heavy snow cover, birds find it a little more difficult to find food and my bird feeders are a constant source of activity in feeding numerous species of birds. I also put pieces of apple on my platform feeder as the mockingbirds really like the fruit and they will spend quite some time feeding on them.
White-throated Sparrow Carolina Chickadee
One of the things that I have been asked numerous times over the years is: “how do little birds, like chickadees, survive the extreme cold”? Well, even our cold temperatures are not anywhere close to the temperatures that Boreal Chickadees of Canada and Alaska are exposed to. There, those species, which are just a little bigger than our Carolina chickadees but still weigh less than an ounce, are exposed to temperatures of 40 below zero. Even more astounding is that most birds have “operating” temperatures considerably higher than that of people. Chickadees keep their body temperature about 104 degrees. Their feathers trap air and are great insulators from the elements and they squat down at night, so that their legs and feet are covered by their feathers. What is vitally important, however, is the caloric intake and the amount of food a bird can find during its activity period and this is what keeps these little birds right on the edge of survival during extremely cold weather. They have to take in enough food each day to insure that their high metabolic rate keeps vital body organs functioning through the night in keeping them warm. All it takes is one day of not being able to find food and the little birds are not able to keep their engines running hot and thus perish during the night.
Another question that I am asked quite frequently is: “how do birds like ducks and geese, stand on ice for long periods of time and swim with their little feet paddling in the frigid water during the winter”? While this seems uncomfortable and unimaginable, cold tolerant bird species have marvelous physiological adaptations that allow them comfort while standing on ice or swimming in very cold water. First the tiny blood capillaries that feed their legs and feet with blood are entwined with the small capillaries that return the blood to the body. Therefore, blood that is cooled in the feet is warmed prior to returning to the body by the warm blood flowing into the feet. This is important so as not to cool the body and vital organs. In addition many species have a very unique system whereas the little capillaries have valves, almost like sphincters, that open and close and only supply enough blood to the feet to keep the tissue alive. So, great volumes of blood are not required to keep the feet warm and much of the blood remains in the body of the bird. Also, birds, when getting a little chilled, may stand on one leg and pull the other up next to the body underneath the feathers. Here the foot is warmed. When quite cold, a bird may also lay, breast down on ice and bring both legs and feet underneath its feathers and only feathers are exposed directly on the ice. Lastly, ducks and geese have scales on their feet and the tissue is not the same as is the flesh on people. The scales do not have the same type of nerve endings nor are they the same sort of living tissue that people have, thus are not prone to frostbite as are the sensitive tissue of hands and toes of people.
Canada goose standing on one leg to conserve warmth.
Not all birds are cold weather tolerant and the Eastern Bluebird, which is a common resident in the Atlanta area, suffers during extreme cold and when there are lengthy periods when snow covers the ground. This is mainly due to not being able to find food but they also do not seem to be able to tolerate extremely cold times. Bluebirds, during the winter, feed on fruits (berries) and they will feed on some suet types at feeders. In addition, I put mealworms out for bluebirds during the colder times, like what we are currently experiencing in the Atlanta area and I also do this during early spring if we get a late cold spell. Female bluebirds are often on eggs or feeding young early in the year and sometimes they have difficulty in finding insects to feed their young. The mealworms get them through a short cold snap, which we sometimes experience in March or even early April. During the winter, however, many bluebirds will often enter a bird house or tree cavity and the bodies of 6 or 7 bluebirds will provide additional warmth when a bird roosting by itself may not survive a cold night. Researchers have reported that as many as 20 bluebirds may take advantage of a communal roosting site where the bodies of many provide additional warmth to the individuals. Even this tactic, however, sometimes does not protect them and when single digit temperatures occur, bluebirds may perish due to the cold. It is always an unpleasant experience to check a bird box and find multiple dead adult bluebirds in the box…… this does occur on occasion.
Male Eastern bluebird enjoying a dish of mealworms on January 11th, a big snow day in Atlanta.
Mockingbird enjoying some apple! Red-bellied woodpecker
Birds are marvelous creatures and even though our knowledge has greatly increased due to amazing technologies that allow us to more fully understand bird physiology……we still have much to learn. In the meanwhile they are an absolute joy to observe.
Keep your feeders full and provide a variety of foods for your feathered friends during these unusual snow events in the Southeastern U.S.