Winter weather here in Michigan is pretty variable. Today the temperature is supposed to get up into the 50s, but other days the high may be much closer to 0F.
Migratory birds like ducks and geese generally head south for the winter, but songbirds stick around. The interesting thing is that you don’t seem to see them on very cold days; it’s not until the temps get into the upper 20s that you start to see them flitting around.
So what are they doing on the very cold days? Presumably they need to eat/drink then too, but I don’t see them out foraging. Are they somehow able to subsist for several days without eating/drinking?
Generally they will tuck themselves into some sheltered place like in conifer foliage or clusters of dead leaves to minimize exposure. And they are out foraging; they just minimize the time they are out in the open.
So on warm days when they’re out and about much more, what are they doing with their time that they’re not doing on cold days? Pursuing mating opportunities?
In the winter they’re just trying to survive. On warmer winter days they will spend time looking for food beyond the bare minimum to put on some fat. In the spring, when there’s more food around, they’ll eat more and use the energy for singing, courtship, defending territories, and laying eggs.
Spending more energy in hopes that it’ll gain them more food? Even animals that don’t hibernate bulk up for the winter, but I’d be surprised that they didn’t take advantage of warmer days when foraging will cost them fewer calories to do.
My back yard. One of the rooms of this house is apparently poorly insulated, and one very cold days there are often dozens of birds tucked up against the foundation.
Birds are pretty tolerant of cold weather. They can fluff their feathers to give them good insulation. Birds do not fly south because it is too cold for them, they fly south because in winter they no longer have access to the food they need.
In far northern locations, if there is water that is kept open (like hot water outflow from industrial plants), waterfowl might stay all winter. But ducks and geese move south when ice freezes over all the food sources where they can forage.
Boreal bids do just fine when it is minus 50, they are not biologically equipped to endure colder temperatures any more so than tropical birds. But they can stay in the north all winter because the food supply (tree-borne seeds, mostly) remain abundant and accessible when it is very cold. Birds that eat, say, flying insects, would starve quickly in a Nunavut winter.
They’re hopping around in the snow, under a sagging arbor vitae, happily eating the seeds I tossed there.
ETA: (Hm. I could say something very naughty about ‘tossing my seeds’.)
