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How birds stay warm

This winter might be a good time to feed the birds if you haven’t done so before.

Ranger Steve’s Nature Niche

By Ranger Steve Mueller

Many birds stay warm by migrating to warmer climes. Even more important for migrators is locating to places where they can find adequate food. Many birds that depend on insects, worms, and other invertebrates find moving to a winter home with adequate food is essential. Some that eat invertebrates stay in cold country but change their diet to vegetation and feed heavily on berries or even buds in winter.

American Robins that stay in our area move from our yards to swamps. I have been seeing robins during the last week of November and I am sure we will find many during the Christmas Bird Count on December 29. Come join us and discover what species are around in winter.

One of the most important ways birds stay warm in cold weather is by eating enough calories daily to maintain body heat. It appears this winter has a scarcity of food farther north. Evening Grosbeaks that we have not seen locally in years are making an appearance. Common Redpolls arrived in open country. Pine Siskins arrived at feeders after Thanksgiving. I did not expect them to arrive this early. Saw-whet Owls are reaching southward. This might be a great year to begin feeding birds if you haven’t maintained winter feeders.

As for staying warm, watch birds at your feeder on warm and cold days to notice differences in appearance and activity. I have not timed the frequency of birds returning to get seeds on cold verses warm days to learn if their foraging behavior changes. It seems they come and go more rapidly on cold days. It is difficult to keep track of a particular bird to monitor its behavior when several of the same species are visiting. Perhaps one will have feathers that make it distinguishable from others of its kind. Watch that bird and note the frequency of visits. Hopefully you will be able to observe it on both cold and warm days.

One of the most obvious things to notice is how birds look heavier in cold weather. They fluff their body feathers called contour feathers to trap air. The trapped air insolates and reduces heat loss. Small contour feathers are numerous and more abundant in winter. If feathers get wet they pack and do not insolate. You may have noticed this with a down sleeping bag. Birds have a preening gland at the base of their tail. They use their bill to gather waxy oil from the gland and spread it on feathers much like we use waterproofing oil on our boots.

Waterfowl, like ducks, geese, and swans, have a massive quantity of down feathers that keep them warm in winter while they float or swim in frigid water or lay on ice. If their down gets wet, the bird’s life will be short. Another vital adaptation to their aquatic nature niche is how blood circulates to and from their feet. Warm blood traveling in arteries to the feet flows adjacent to veins carrying blood from their feet. Heat from hot blood on the way to feet is transferred to cold blood returning from the feet. Cold blood is warmed by the veins touching warm arteries before blood reenters the body. The hot blood in route to feet is cooled. Instead of losing the heat to the environment, some heat is conserved by being transferred to the cold blood before it returns to the body.

It might not seem like a big deal but having moderately warmed blood entering the body instead of cold blood means the bird does not need to consume as many calories to maintain its body temperature. Watch birds like gulls standing on the ice to notice they often stand on one foot and tuck the other to the body. When watching behavior, determine if birds are facing the wind or away from the wind. When facing the wind, the air flows over the feathers and they are not ruffled to let cold air enter like when the wind approaches from behind.

Little things spell life and death. Like us, they can generate heat by increasing physical activity but this is only effective when they have enough food to replace lost body fat. During the night, a bird can consume its fat and starve in extreme cold. Black-capped Chickadees can go into a hibernation-like torpor where their heart rate and metabolism are reduced on long winter nights preventing too much body fat loss causing starvation.

These are some major methods employed to survive cold weather. Birds do not directly say thank you for us providing black oil sunflower seeds and suet but increased use of feeders in cold weather tells us they are appreciative.

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at odybrook@chartermi.net – Ody Brook Nature Sanctuary, 13010 Northland Dr. Cedar Springs, MI 49319 or call 616-696-1753.

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