How Cold Is Too Cold for Wild Birds?

The short answer

• No air temperature on its own is too cold for a healthy wild songbird. Chickadees and tits winter in forests where it reaches -4 to -22 °F (-20 to -30 °C).
• The working line is about 0 °F (-18 °C) held for days. In a study of Black-capped Chickadees, birds with feeders survived the winter at 69% against 37% without, and the gap opened mostly in months with more than 5 days below that mark.
• A small bird gets through a cold night on fat it gained that day, about 0.74 g for a chickadee, and by letting its body cool from about 108 °F to about 95 °F. That cooling saves far less at -4 °F than on a mild night, so fat carries the hardest nights.
• Freezing rain can be worse than deep cold. It seals seeds, buds and bark under glaze, and after the 1998 ice storm, counts of chickadees, jays and woodpeckers fell more in iced areas than outside them.
• What to do: keep feeders full through any run of days near 0 °F, fill before dusk, and switch to hulled foods when ice is forecast.

No air temperature on its own is too cold for a healthy wild songbird. The number that matters is about 0 °F (-18 °C), held for days. In a study of Black-capped Chickadees, birds with feeders outlived birds without them mostly in months with more than 5 days below that mark. And the weather that does the most harm is often freezing rain near 32 °F, not dry cold far below it.

Most answers online for this question are about pet parrots and backyard chickens. Those birds live in cages and coops, and their numbers do not carry over to a chickadee in a spruce.

What "too cold" means for a wild bird#

For a wild bird, too cold does not mean a reading on a thermometer. It means a night longer and colder than the fat the bird stored that day can pay for. Cold sets the size of the bill. Food and daylight decide whether the bird can pay it.

Two terms carry the rest of this page.

Nocturnal hypothermia is a controlled drop in body temperature at night. The bird turns its own thermostat down to lose less heat. It is not the same as the illness people call hypothermia, and the bird warms back up at dawn.

Freezing rain is, in the National Weather Service's words, rain that falls as a liquid but freezes into glaze on contact. An ice storm is a long spell of it.

How a chickadee gets through a cold night#

Small birds run hot. Chickadees and tits of 10 to 13 g hold a daytime body temperature of 41 to 43 °C (about 106 to 109 °F) in winter, say Anders Brodin, Jan-Åke Nilsson and Andreas Nord in a 2017 paper in Oecologia. At night they can let it fall to about 35 °C (95 °F).

That saving is real, but it shrinks as the night gets colder. By the authors' figures, an 11.5 g bird that drops 8 °C (about 14 °F) saves 35% of its night energy at 20 °C (68 °F). At -20 °C (-4 °F) it saves only 10%. On the coldest nights, fat has to cover almost the whole bill.

So the bird eats all day to build that fat. The paper puts the daily gain at about 0.74 g, typical for a Black-capped Chickadee in winter. That is almost a tenth of its lean body mass, every day.

The cooling still matters a great deal. In their model, a bird that saved 30% of its night energy this way had a 71% chance of getting through the winter, against 13% without it. The abstract sums it up as a 58% gain in survival over a 100-day winter.

North American birds do the same thing. Sheldon Cooper and James Gessaman measured Mountain Chickadees and Juniper Titmice in Utah. Both cooled down at night all year, by 3 to 11 °C (about 5 to 20 °F) below their daytime level. That saved 7 to 50% of night energy in the chickadees and 10 to 28% in the titmice.

Where the 0 °F line comes from#

Brittingham and Temple compared chickadees with and without feeders in a study published in Ecology in 1988. Birds with feeders survived the winter at 69%. Birds without them survived at 37%. Monthly survival was 95% against 87%, and fed birds were 0.13 g heavier.

The key line is about timing. The survival gap opened mainly in months with severe weather, which the authors define as more than 5 days below -18 °C. That is -0.4 °F, so call it 0 °F. In those months, they write, high energy demand probably made it hard for unfed birds to get enough from scattered natural food.

So if you travel during a spell like that, ask a neighbor to keep the feeders full. In an ordinary month, the study points to a much smaller gap, and a few days away matter less.

That is the honest answer to "how cold is too cold". A night at 0 °F is not the problem. A week of them is.

A cold week, walked through#

Take a chickadee on the edge of a town in the upper Midwest in January. Suppose a cold front brings six days in a row with lows below 0 °F, and some nights near -4 °F.

The nights. The bird can still cool itself to about 95 °F. But at -4 °F, by the Brodin figures, that saves only about 10% of the night's energy. Most of the bill comes from fat.

The days. The bird has to put back about 0.74 g of fat before each dusk. Days are short, so it has fewer hours to do it. With no ice, its natural food is still out there. It is just scattered and slow to find.

The month. Six days below 0 °F puts this January past the 5-day mark. In the Brittingham and Temple study, months like this are where most of the gap between fed and unfed birds appeared.

The feeder. A full tube of black oil sunflower and a cake of suet let the bird refill fast. Filling before dusk matters most, as the two-fill routine on winter bird feeding explains. Now suppose the feeder runs empty on day three. The bird has to spend more of its short day searching, in exactly the kind of month where unfed birds fell behind.

Why ice can be worse than cold#

Freezing rain changes the problem. The air may sit at 30 °F, warm by winter standards. But seeds, buds and bark go under a shell of glaze, and the food is there but cannot be reached.

A North American record comes from the January 1998 ice storm. It brought five days of nearly non-stop freezing rain to Quebec, with temperatures below 0 °C (32 °F). Blais, Savard and Gauthier compared Christmas Bird Counts from before and after it, in 15 iced areas and 16 areas outside the storm.

Counts of Mourning Dove, Rock Dove, Hairy Woodpecker, Blue Jay, Black-capped Chickadee and House Sparrow fell more in the iced areas. Brown Creeper and Downy Woodpecker were also down there. Only the European Starling showed a clear rise there. Birds of open country that feed on the ground came through better than birds that feed in trees. The authors call the effect quite significant.

Ice also works on the bird itself. Laura Erickson, writing for her For the Birds program, notes that when ice coats feathers, birds lose both their insulation and their ability to move. She also notes that birds roosting in tree holes have been sealed in by thick ice.

What to do at each temperature#

Each row below comes from a ruling made above.

For freezing rain, the site's own feeder fixes apply. Sunflower hearts and shelled peanuts stay loose when in-shell seed welds into a crust. A hopper feeder with deep eaves keeps glaze off the seed. Erickson's advice for ice is cover as well as food, which means shrubs and evergreens near the feeders, as set out on native plants and cover.

Water runs short in a hard freeze too. A heated bath keeps a patch open; setup is on bird baths and water, and running cost on heated bird bath cost to run.

Which birds the evidence covers#

The figures on this page come from chickadees, tits and titmice. That makes them a close guide for the Black-capped Chickadee and the Tufted Titmouse, the small clingers that spend winter in trees.

The ice storm study widens the list. It found counts of the Hairy Woodpecker, Downy Woodpecker and Blue Jay down after the storm. The European Starling went the other way.

What this page does not cover#

This page is about healthy wild songbirds outdoors. It does not apply to pet birds, chickens or ducks, which live in shelters people control. It does not cover hummingbirds, which have their own cold problem: see nectar freezing point and the Anna's Hummingbird profile. A bird that sits fluffed and will not fly off is more likely sick than cold, and the signs are on bird diseases at feeders.

The 0 °F line is one study's definition of a severe month, not a proven threshold for every species. The abstract does not say whether it counted daily lows or daily averages. The survival figures are for chickadees, and the 58% gain is a computer model, not a field count. Feeders help most in hard spells, but birds do not depend on them, as do birds depend on feeders sets out. For the rest of the year, use the feeding calendar.

Frequently asked questions#

What temperature is too cold for wild birds?

There is no single number. Chickadees and tits winter in forests where nights fall to -4 to -22 °F (-20 to -30 °C). The closest thing to a line comes from a study of Black-capped Chickadees: birds with feeders outlived birds without them mainly in months with more than 5 days below 0 °F (-18 °C). So a run of days near 0 °F is when cold starts to cost lives, and a single cold night is not.

Can wild birds freeze to death?

Yes, but cold rarely acts alone. A small bird dies on a cold night when it runs out of the fat it stored that day. Ice is the other danger: Laura Erickson notes that when ice coats feathers, birds lose both their insulation and their ability to move, and that cavity-roosting birds have been sealed into trees by thick ice.

How do small birds survive freezing nights?

Two ways. They eat hard all day and go to roost with fat to burn, about 0.74 g for a chickadee. They also let their body temperature fall at night, from about 108 °F to about 95 °F in chickadees and tits. That controlled cooling, called nocturnal hypothermia, cuts the heat they lose. A model of a small tit found it raised the odds of surviving a 100-day winter by 58%.

Is freezing rain worse for birds than snow or cold?

It can be. Freezing rain falls as liquid and freezes into glaze on contact, so seeds, buds and bark end up under a shell of ice. After five days of freezing rain in Quebec in January 1998, Christmas Bird Counts of chickadees, Blue Jays and Hairy Woodpeckers fell more in the iced areas than in areas outside the storm. Ground feeders of open country came through better than birds that feed in trees.

Do birds need my feeder when it is very cold?

Not most of the time. But in a long cold spell it can matter a great deal. In the chickadee study, birds with feeders survived the winter at 69% against 37% without, and most of that gap came in months with more than 5 days below 0 °F. That is the time to keep feeders full and to arrange a neighbor if you travel.

Sources and further reading

1. Impacts of supplemental feeding on survival rates of Black-capped Chickadees (Brittingham and Temple 1988, Ecology 69(3):581-589) Penn State, abstract Monthly survival 95 vs 87%, over-winter 69 vs 37%, 0.13 g heavier; difference mainly in months with more than 5 days below -18 °C
2. Adaptive temperature regulation in the little bird in winter (Brodin, Nilsson and Nord 2017, Oecologia 185(1):43-54) PubMed Central, open access Day body temperature 41-43 °C, night down to 35 °C; about 0.74 g fat a day for a 10-13 g tit or chickadee; savings 35% at 20 °C, 10% at -20 °C; modeled survival 0.13 to 0.71, 58% over 100 days
3. Nocturnal hypothermia in seasonally acclimatized Mountain Chickadees and Juniper Titmice (Cooper and Gessaman 2005, The Condor 107(1):151-155) BioOne Both species used nocturnal hypothermia year round, night body temperature 3-11 °C below day, savings 7-50% in chickadees, 10-28% in titmice
4. Impact of an ice storm on resident bird populations in eastern North America (Blais, Savard and Gauthier 2001, The Forestry Chronicle 77(4):661-666) Canadian Institute of Forestry January 1998 storm, five days of freezing rain below 0 °C; Christmas Bird Counts in 15 affected and 16 control areas; tree foragers hit harder than open-country ground feeders
5. Ice Storms (For the Birds radio program, 2 April 2007) Laura Erickson Ice on feathers costs insulation and mobility; cavity roosters sealed in by ice; cover and food as the backyard response
6. Glossary: freezing rain NOAA National Weather Service Rain that falls as a liquid but freezes into glaze on contact