Winter can be a tough time for birds, from even the simplest of daily tasks becoming a bigger challenge during this time of year. From finding food, to avoiding becoming food for someone else, to just trying to stay warm in temperatures that could drop into the negatives. But birds are resourceful and have adapted to surviving through all these challenges that they may face day to day.
Some birds in response to the seasonal changes may migrate south, those trips can be short or long distance depending on the species. These journeys though can be very dangerous and very energy consuming and have their own unique challenges and threats.
The birds that don’t migrate south and into warmer climates that have more plentiful food, have to survive the harsh conditions brought on by the change in their environment. From low temperatures, to there being less plentiful food with even less daylight to find said food.
By staying, each bird faces two main challenges, staying warm and finding food. Even when temperatures drop into the negatives, birds will need to maintain their body temperature of about 105 degrees. Food, while readily available in the warmer times of the year, now becomes a challenge as there are few insects, berries and seeds available. What food that is available may be even more difficult to find due to snow and ice.
One of the keys to surviving in cold temperatures, especially when temperatures can drop into the negatives, is staying warm. To help stay warm in these frigid temperatures, birds employ different tactics to keep their body temperature up. You may have noticed on a particularly cold day, that the birds in your backyard appear extra fat or fluffy. Their layers of different feathers are perfect for insulation and trapping in body heat. They work the same way a nice big puffy jacket would. They can puff up their feathers to create a larger layer between their body and the cold air. The first layer to a bird’s feathers are called down feathers, they are small wispy feathers that help trap the warm air against their body. Then are the body feathers, called contour feathers, which are more structured with a vein and barbs and barbettes. When you see the birds plumage and colors, these are the feathers you are seeing. They can be individually moved to lay flat on the body or puffed out. These two layers of feathers help trap and keep the warm air from their body in and avoid losing it to the cold ambient air by creating an insulative layer.
Many species, in preparation for the winter season, will molt in fall. Many species may molt into less flashy plumage as they no longer need to impress a potential mate. Along with that, this molt may also include an increased number of down feathers growing in by about 25%.
Not all parts of a bird are covered by feathers though, like their eyes, beak, feet, and legs. These body parts can lose a lot of body heat, to help with this, they can tuck their heads into their feathers to trap that heat. Their feet and legs also look prone to freezing as they perch on a frozen branch, as these body parts are bare with no insulation. So how do they not freeze or even lose most of their body heat through them? That is because their legs and feet do get close to the ambient temperature, sometimes down to about 30 degrees. These appendages will be kept cold to help preserve their high body temperature. They don’t freeze though, blood continuously brings heat from the bird’s body to these body parts and heats the veins of cooled blood returning from the feet, then it returns back into the bird’s core where it is reheated and the process continues. If they didn’t do this, the bird would lose too much body heat from these uninsulated parts. With less food available , it would be very difficult for a bird to get enough calories to maintain losing so much body heat.
These temperatures are even tougher on small birds, with small bodies and more surface areas, they are prone to losing their crucial body heat faster than a larger bird would. Small birds, like chickadees and titmice have a body temperature of about 105 degrees, which can be a stark contrast to the ambient temperature around them. To help with this many small species have been known to roost together to help reduce their individual surface area and help to stay warm. During extra cold times or snow storms, some birds will also look for shelter from the weather. Finding shelter in nooks of trees, in the branches of evergreen trees and some species will roost in tree cavities.
Nights in winter can be particularly tough for birds, where temperatures drop but birds are unable to forage for food. One adaptation that is used to preserve calories at night, is to dip into a state called regulated hypothermia. They will drop their body temperature down sometimes as much as 22 degrees to help conserve their energy. A less common strategy used to conserve energy is called torpor. This is a more extreme method that is common to hear associated with hummingbirds, where a bird will drop their temperature from about 105, all the way down to about 50 degrees. This allows them to use drastically less calories. After waking up from their nightly torpor, they begin by shivering to help warm themselves up.
With the colder temperatures, and less food, food becomes even more important to survive. To stay warm and keep their proper body temperature, they need energy. Food contains important calories that fuels this needed energy, but it can also be much harder to find said calories in the winter months. Some species, like chickadees will actually need to consume about 35% of their body weight everyday. Birds that diet requires mostly insects tend to migrate, as this season lacks availability while others that have a more varied diet may stay, where during the winter they may rely on mostly seeds to survive. This isn’t a steadfast rule but just a general trend as it is not too uncommon in a New York winter to see a brown creeper going up and down a tree trunk in its search for insect larvae in cracks in the tree’s bark.
To help with the fact that food can be hard to find, species like chickadees will cache food. Caching is a technique used to hide and store food for when times are less plentiful. Chickadees, small non-migratory songbirds that only weigh 9 to 14 grams, are amazing examples of bird adaptations to survive these harsh winter conditions. They will cache extra food they find, each in an individual spot. A single chickadee can cache away thousands of individual seeds and other food items in a year. But that is a lot of different locations to remember where they hid their food. To help with this, chickadees and other birds’ brains actually grow in size during this season. Their hippocampus can actually enlarge by about 30%. The hippocampus is part of the brain that is devoted to spatial memory and allows them to remember most of their food hiding spots. This seasonal enlargement is greater in northern latitudes and in higher elevations, even within the same species.
Another strategy used to help survive during the winter months is by forming mixed species flocks. This is a good example of the saying ‘safety in numbers’. With many birds together, that means there are more eyes on the lookout for potential predators. At the same time, this allows them more time to actually forage for food.
So how can you help these birds in this harsh season? There are several things you can provide in your own yard that your local birds would greatly appreciate. Providing high energy food such as suet, peanuts and sunflower seeds is something easy that can help supplement a bird’s diet and give them some extra calories. Water is something that can be difficult to get sometimes, providing a heated bird bath can give birds easy access and you may even be surprised to see several birds in winter using it to take a bath. When planning your yard and landscaping, there are also several additions you can make to help birds year round. Installing roosting and nest boxes, as well as leaving dead trees with cavities, can give birds places to seek shelter not only in winter but also during breeding season for places to nest. When landscaping, use native plants that can provide shelter and provide food. Evergreens can give your birds a place to get shelter from the weather and from potential predators like hawks. Planting fruit and berry plants that provide food during different times of the year, from spring to plants that have fruit into fall and winter, can attract birds such as robins and cedar waxwing even in the middle of winter. These examples can make your yard more bird-friendly and help the birds year round.
References:
Winter for Black-Capped Chickadees
How Do Birds Survive the Winter?