Birds have amazing abilities to survive in cold weather conditions. Their feathers provide excellent insulation against the cold. Many species grow extra feathers in the fall to prepare for winter. Small birds also conserve body heat by fluffing their feathers up to create air pockets. This traps their body heat close to their skin. Birds can survive temperatures well below freezing as long as they have access to food sources. However, extreme cold combined with wind, ice, and snow can threaten their survival.
What temperatures can birds withstand?
Most small birds can survive temperatures as low as -20 to -30 degrees Fahrenheit if they have abundant food, shelter from the wind, and place to roost. Larger birds like geese and ravens can withstand even lower temperatures below -40 degrees Fahrenheit. The lowest recorded temperature survived by birds is -93 degrees Fahrenheit endured by Willow Ptarmigan in Alaska. Birds are found living year-round in some of the coldest places on Earth like Antarctica and the Arctic. Their specialized feathers, fat reserves, and adaptations allow them to not just survive, but thrive in frigid environments.
How do feathers keep birds warm?
Feathers provide exceptional insulation for birds. They have a branching structure that traps air and creates a layer of dead air around the bird’s body. This layer of trapped, non-moving air acts as excellent insulation to retain body heat. The more dense and fluffy the feathers, the better they are at trapping air and keeping the bird warm. Many species grow extra dense plumage in fall and winter to provide warmth. Birds can also control the insulation factor of their feathers by fluffing them up or sleeking them down. Fluffing feathers traps more air, while sleeking them releases air and allows for heat loss.
Do all birds grow winter feathers?
Many temperate and arctic bird species grow special dense winter plumage. Some examples include:
- Cardinals grow extra thick feathers, increasing their plumage by up to 50% in winter.
- Chickadees allow more down feathers to come through their regular feathers for winter insulation.
- Redpolls grow extra long down feathers under their contour feathers in winter.
- Ptarmigans turn completely white in winter to their plumage provides camouflage in snow.
- Snowy owls grow extremely thick feathers covering even their legs and feet to withstand perching on snow and ice.
However, some birds do not grow special winter plumage if their regular feathers already provide adequate insulation. Examples include woodpeckers, crows, jays, and ravens. Their sturdy contour feathers give sufficient warmth year-round.
How do small birds stay warm?
Small birds are at higher risk of heat loss because of their high surface area to volume ratio. They compensate through several behavioral adaptations:
- Fluffing feathers – Fluffing feathers traps layers of air to retain body heat.
- Tucking head under wing – Tucking their head reduces exposed surface area and allows body heat to warm the head.
- Huddling together – Some small birds huddle or roost communally to share warmth.
- Shivering – Shivering generates muscle heat. It is used to warm up on very cold days.
- Sunning – Sitting in sunny spots warms feathers and lifts body temperature.
Small birds also eat frequently to fuel their high metabolisms that produce internal heat. Their high energy diets of insects, seeds, and berries provide plenty of calories to generate heat all day.
Do bird feet get cold?
Birds’ feet are made to withstand freezing temperatures. Their legs and feet lack the insulating feather coverage of their bodies, but they have a built-in central heating system. Arteries carrying warm blood from the body run right alongside veins carrying cool blood from the feet and legs in a Countercurrent heat exchange system. The warm arterial blood transfers its heat to the cooler venous blood, keeping the feet from freezing.
Birds also have tendons that automatically constrict blood vessels in their legs when temperatures drop. This reduces blood flow to the extremities so less body heat is lost from the feet. Their scaly skin and tough keratin scales also resist freezing. Most small birds keep their feet from freezing by frequently perching and fluffing feathers to cover their toes.
Do all birds migrate or hibernate in winter?
Not all birds leave their breeding grounds for warmer climates in winter. Which birds stay or go depends on available food sources. Birds that depend on insects or nectar must migrate south or perish when their food sources disappear. Examples are warblers, hummingbirds, swallows, and swifts. But birds that can switch to seeds, berries, and small mammals in winter often remain in their breeding territory year-round. Examples include chickadees, titmice, woodpeckers, grouse, crows, and owls. Even within a species, only the far northern populations may migrate south. More temperate populations can withstand cold winters as long as they have access to food.
Some birds partially hibernate or go into a torpor to conserve energy on extremely cold nights. Their body temperature and metabolism drop, allowing them to roost in a dormant state until morning. Birds that exhibit torpor include hummingbirds, nightjars, and poorwills.
Adaptations of arctic birds
Birds living in the arctic and antarctic have specialized adaptations for withstanding bitter subzero temperatures. Besides having the densest plumage of all birds, other adaptations include:
- Compact round body shape – Minimizes exposed surface area.
- Countercurrent heat exchange in legs – Retains body heat in core and prevents foot frost bite.
- Modified bill structure – Prevents freezing or frost damage.
- Feathered feet and legs – Insulate and prevent freezing.
- White winter plumage – Camouflages them against the snow.
- Featherless eye ring – Prevents frost build up that could blind them.
- Shortened extremities – Reduce amount of tissue vulnerable to freezing.
- High fat reserves – Provides energy for generating heat.
- Down lining in nests – Insulates incubating eggs from the cold ground.
Do cavity nesting birds stay warmer?
Cavity nesting birds gain considerable warmth benefits from nesting in enclosed tree cavities or nest boxes. The cavity shields the nest and birds from cold winds and weather. The outer tree wood also provides excellent insulation from temperature extremes. Studies show cavity temperatures average 15-20 degrees warmer than the outside air temperature. However, cavities can also overheat babies on hot summer days if adequate ventilation is not provided. Some ways cavity nesting birds stay cool in summer include:
- Sit at cavity entrance where air flow is greatest.
- Wear wet feathers during incubation.
- Pant to evaporate water and dissipate heat.
- Flutter wings to circulate air.
- Leave nest periodically.
So while cavities provide shelter from the cold, their enclosed space poses overheating risks in hot weather that birds must mitigate through behavioral adaptations.
Winter feeding tips
Birds benefit greatly from extra food sources provided by humans during harsh winter weather. Here are some tips for feeding birds in winter:
- Provide both seeds and suet or peanut butter. Seeds give energy while fat provides calories for generating warmth.
- Use mesh bags or platform feeders to minimize build up of old, moldy food.
- Site feeders in sheltered spots protected from wind and rain.
- Place feeders close to trees or shrubs to provide quick escape cover.
- Clean feeders regularly to prevent disease transmission.
- Provide fresh water for drinking and bathing. Use heaters or replace it often to prevent freezing.
- Put feeders out before winter storms so birds can stock up on food.
- Supplement natural foods by planting berry producing shrubs and trees.
With good planning, backyard birders can create an essential winter refuge filled with shelter, water, and nutrition to help local birds survive the toughest weather.
Signs of hypothermia in birds
During extreme cold spells, some birds may develop hypothermia if they cannot find adequate food and shelter. Signs of hypothermia in birds include:
- Shivering – Earliest sign as they try to warm up.
- Fluffed up feathers – Trying to trap body heat.
- Lethargy – Sitting with eyes closed, barely moving.
- Weakness – Unable to fly or grip tightly.
- Disorientation – Confused, may not flee.
- Uncontrolled head movements or seizures.
- Staggering or falling off perches.
- Labored breathing.
- Coma and death.
Birds suffering hypothermia need immediate warming and rehydration. Providing a heat lamp, warm indoor area, and fluids can help stabilize their condition. Once warmed, get them to a wildlife rehabilitator quickly for supportive care. Prevent hypothermia by ensuring birds have access to winter food and roosting sites before extreme weather hits.
Conclusion
Winter weather presents considerable survival challenges for birds. But with adequate food sources and shelter, most species have evolved adaptations enabling them to withstand freezing temperatures and winter storms. While prolonged extreme cold can overwhelm their survival abilities, birds are incredibly resilient to cold. Providing extra food, water, and roost boxes can help local birds endure winter and gives us the chance to enjoy their beauty and songs even on the bleakest winter day.
