For the Birds Radio Program: February Thaw

Original Air Date: Feb. 15, 1991

Warm weather in winter is a mixed blessing. (Date confirmed)

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It’s not unusual to have a day or two of unseasonable weather in February, but last week’s warm spell was truly unprecedented. Suddenly robins were turning up in people’s lawns, trees were threatening to bud out, and winter looked pretty much over.

Warm weather in winter, like just about everything else in life, is a mixed blessing. A few species of birds do get spring fever and move north before it’s really safe. Male robins are always among the first to arrive. The bulk of them follow the 37-degree isotherm, but some move when the average temperature is even lower. The first to come get top choice for prime breeding territories, which is a pretty big advantage as long as they actually survive. The competition between daring early migrants and safe but late ones has been part of robin evolution for tens of thousands of years. The years when early thaws are followed by mild conditions, the early migrants raise extra babies, maximizing their reproduction. In years when many of the early migrants die in bad weather, the robins genetically predisposed to migrate later have the advantage. Over the long run, both groups keep going. Fortunately, many robins are flexible enough to turn around and head south again if bad weather returns.

Mild weather, even for a few days, is great if you’re a northern finch or a chickadee. These species aren’t much into skiing or hockey, so thawing snow doesn’t screw up their leisure time. Little birds keep warm in part by shivering. A chickadee’s muscles are in a constant state of shivering as long as the temperature is lower than about 64 degrees, which means those tiny sprites burn up a lot of fat. By February, their fat reserves can be pretty much exhausted. A mild spell gives them an opportunity to stuff their little faces and replenish their supplies once again.

And even more than food, these thaws provide birds with real drinking water. Eating snow not only doesn’t quench thirst, it also quickly lowers body temperature. Birds often gather at dripping icicles and roadside puddles on a sunny winter day. For them, fresh drinking water is as welcome a treat as champagne is for a World Series winning team.

During mild weather, birds can eat their fill with time to spare, which they use for several purposes. The better the weather, the more time chickadees and woodpeckers have to sing or drum out their mating songs, sealing their pair bonds for another breeding season. And in good weather, birds spend more time away from their tried-and-true feeding grounds, searching out backup systems just in case. The chickadees that get most of their winter food around my feeder spend nice days cruising the neighborhood looking for other feeders and good trees. As soon as the weather gets bad, they come back to my place, but this method gives them insurance just in case my feeder runs dry.

During nice weather, some people complain about lousy skiing conditions, and others spend the entire nice period worrying about how bad the weather will be as soon as the warm spell is over. Chickadees take the weather as it comes, rejoicing in pleasant days, but somehow finding beauty and cheer in raging blizzards as well. No matter what the weather, it’s nice to spend it with a chickadee.