I'm not really as much of a winter person as some people are. I don't mind a bit of it, and I used to relish winter for tobogganing, playing hockey on the pond, snowshoeing, cross-country skiing and the like. But I am fascinated by the way the numerous types of plants and wildlife survive the wintry elements, and I don't mind sitting in a warm environment pondering some of these mysteries.
I have been reading a book entitled "Life in the Cold: an introduction to winter ecology", by Peter J. Marchand, a professor in Vermont. It deals a lot with the physics side of things, regarding heat transfer, the effects of short-wave vs long-wave sunlight radiation, etc. and how the many species of flora and fauna deal with the cold. Physics was never one of my strengths, and I found my eyes glazing over in some parts of the book, but other parts were much clearer to me. So some of the following is what I learned from this book regarding birds.
Of course as we know, many birds fly south, especially those which require insects or open water. But we have lots of resident species which may alter their diet from insects during the warmer periods to seeds during the colder months. By not flying hundreds or thousands of kilometres south to avoid winter, they save a lot of energy. Those that do migrate risk numerous hazards along the way. That isn't to suggest there aren't hazards by staying here in the winter. And to some of the really northern species, such as this Snow Bunting in the following photo, southwestern Ontario is already hundreds or thousands of kilometres south, so they've already experienced some migration hazards and may experience more while they are here.
The key to survival is to minimize heat loss. For mammals, eating enormous amounts of food in the fall to add fat layers is a common strategy. Birds cannot add much fat, however, since it would interfere with the mechanics of flight. In most cases, especially for smaller songbirds, they can only add enough fat to enable them to survive for a day or two before refuelling becomes more critical.
Some birds will find places of shelter in which to roost. It may be an old woodpecker hole, or a dense evergreen from which to escape the effects of the wind and extreme cold. On occasion, more than one bird will use the same shelter, using the 'huddling' effect to share heat and conserve energy. However they had better ensure that a Raccoon or an Eastern Screech Owl isn't already using the hole!
|used Pileated Woodpecker hold|
But please, residents of Chatham, do not start praying for those conditions again. While many crows perished, they were the obvious ones victims of this extreme weather. Many smaller birds died as well!
Another strategy used by some birds, including Black-capped Chickadees, is to go into a state of partial torpor. Hummingbirds are well known for this strategy.
What about those birds that spend a lot of time on the snow, or in water that is just barely above freezing? Wet feathers are an immediate danger, as mentioned above in the discussion on crows, but some species of waterfowl dive into the freezing water frequently to obtain food. The natural oil in the feathers keeps the feathers from getting wet as long as it is replenished by the bird's oil glands.
Food supply can be a problem, when the ice gets too restrictive and prevents the birds from accessing what they need. Then alternate food sources much help them through the tough times. However in some cases, such as this Redhead below, feeding on zebra mussels isn't part of its normal diet. It may help them through for a short time, but some of them won't make it.
|Mallards, American Black Duck|
|Herring Gulls and Ring-billed Gull|
So next time you see a goose standing in the snow on one leg, or a songbird such as this Eastern Towhee doing the same on a branch near a feeder, you will know why it can survive.