As this throwback winter plods on, with ice fishers on the ponds and ice floes on the bay, one of the most common questions us bird folks get is “how do birds survive these brutal temperatures?”
Good question. The first answer is pretty simple – feathers. Feathers, especially the soft inner downy ones, are wonders of natural engineering. The downy feathers, which are wispy and chaotic compared with the more orderly outer feathers, trap heat and block wind, even more so when the birds fluff them up to trap air in them – this is why robins and other songbirds are round on a really cold day. The large ducks known as eiders seem to have the best down of all, which they famously pluck from their own bodies to insulate their nests. Much of the eider down traded globally for use in coats and comforters comes from these nests after the eiders are done with them, mostly from Iceland.
“But what about the parts with no feathers?” you are probably shouting at your radio. Another good question but calm down – I’m getting to that. Bird feet are really cold, such that you wouldn’t want to share a bed with one on a cold night, but they have little in the way of nerve tissue or even water in the cells of the feet – it’s mostly bone and sinew – so they don’t get frostbite or probably feel much discomfort. They also have a special circulatory system where blood vessels coming to and from the body are close together to exchange heat, so the cold blood from the feet gets warmed by blood coming down from the body, protecting the core from that freezing cold foot blood.
That covers the exterior and some of the HVAC system for birds, but you still need a lot of fuel for that high metabolism. A chickadee maintains a body temp that would kill humans, about 108 degrees Fahrenheit, even on these frigid days. To survive the night, however, they basically go into hypothermia to save energy, lowering their core temp about 12 or 15 degrees below normal. But they still need eat enough during daylight to gain 10% of their body weight in fat, every day, then burn that fat overnight to stay alive. That’s like us gaining 15 pounds of fat in between breakfast and bedtime, something I attempted several times over the holidays but failed.
While seedeaters like sparrows and finches and fruit eaters like robins and bluebirds have plenty of food all winter in this world of weeds, it’s the insectivores that amaze me – look outside right now and imagine your survival depends on somehow finding enough insects to stoke your metabolism through another night huddled in a hollow tree. Golden-crowned Kinglets, many of which winter well north of here, are even smaller than chickadees, and eat almost exclusively insects, including their eggs.
In these deep freezes, it seems like birds would have a hard time finding water, but their water needs are less in winter, and some think they get much of the water they need from their food in cold weather. But there are also sneaky water sources even in prolonged freezing weather, like trickles of moving water at stream outflows, groundwater seeps, melting icicles, and even snow, which they will eat. But I am always shocked how little activity I see at my heated bird bath in really cold weather, supporting the idea that water is not as limiting as food is in freezing weather.
Ultimately, the answer to how birds survive this cold weather is that they are just way tougher than we are. All of our technological achievements seem like artifice when you consider that any chickadee can best us on a cold day, even finding the energy to sing a bit. But it’s still hard to watch them with those naked little legs exposed to the cold – does anyone else want to give them little boots? Ok, maybe it’s just me.