By Tommy McCarthy, Environmental Educator

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Many songbird species migrate south for winter - but what about the ones that stick around? We know that many mammals, reptiles and amphibians can hibernate or brumate in winter to survive, but only one bird species is known to hibernate (the Common Poorwill). So how do all the others remain active and continue to spend energy without starving or freezing?

Birds in the winter must maintain a delicate energy balance. By the time the day comes to end, they need to have enough energy from the food they have eaten to keep their bodies warm overnight. Oftentimes, especially for smaller birds, they have no surplus of energy. This means that if you scare a small bird from its sleeping position on a cold night and force it to spend additional energy, it can end up freezing to death before the morning. Because having enough energy is so important, it is vital that birds have reliable food sources in order to survive the winter. This is why bird feeders see so much traffic during the colder seasons. One species you definitely will see at your feeder in the winter is the Tufted Titmouse, and you may be surprised to learn that these charismatic little birds actually did not range as far north as Connecticut prior to around 1940. The steady source of food that bird feeders provide is thought to be part of the reason that they were able to expand their range northward and survive the New England winter weather.

If you have a bird feeder in winter and spend time watching the birds, you may have at one point thought they were getting fat. The birds do indeed have a higher body fat percentage in winter, but what you were observing was probably a different adaptation - the fluffing of their feathers! On cold winter days, birds can look so spherical, or orb-like that the term “borbs” was coined on the internet to describe them. This appearance is not because of weight that they’ve put on, but because of how they can fluff out their feathers to trap the warmth from their bodies in air pockets to retain as much heat as they can. This heat trapping function pairs well with their ability to shiver to generate heat. 

 

But what about the parts of birds that don’t have any feathers, namely their feet? Our toes get nippy even inside of socks and boots! Here, birds just have a higher tolerance for cold than we do. As mentioned before, birds do not have much extra energy during winter. Above all else, they need to use their energy to maintain their core temperature so their vital organs function properly and don’t freeze. This means their bodies do not spend nearly as much energy keeping their feet warm. Black-Capped Chickadees regulate the temperature of their feet at just above the freezing point, and without this biological energy efficiency, it would be unlikely that they could eat enough food to survive the demanding cold climate.

So while birds do not hibernate, it is not as if they are easily surviving the season. The balance they maintain is so delicate that even a tiny amount of unnecessary energy spent can throw it off. Feeding birds in winter is a joyful practice, and having a reliable food source truly must reduce the stress of surviving during such a period. Now when you see the fluffed up birds in your yard, you will truly feel like you are helping and know a bit more about how they are getting by!