By David Bird
Some of Canada’s hardier bird species brave the winter right here at home. They have some good tricks up their sleeves.
If you stood outside in just about any Canadian city during January or February without a stitch of clothing, you'd become a Popsicle in short order. So we don heavy coats, thermal mitts and wool-lined boots. But what about birds? Not all of them head to warmer climes in winter, so how do they cope?
Actually, birds have an amazing number of behavioural and physiological adaptations for surviving the coldest of conditions. It has a lot to do with one of their unique features — feathers. If you're looking for natural lightweight insulation, you can’t find much better.
A) DRESS IN LAYERS
Just like we throw on extra clothing to combat winter cold, some birds enhance their insulation from feathers by moulting into fresh, thick plumage. Some sparrows that spend their winters in chilly areas actually increase their plumage weight by as much as 70 per cent from summer to winter.
Ever watch a bird on a really cold day fluff out all its feathers so that it looks like a little butterball? The bird is simply adjusting its feathers to create warm air pockets to increase the insulation value of its plumage. It’s the same principle as when you buy a winter coat — you want it a bit loose so that your body heats the trapped air to provide an extra layer of insulation.
B) FANCY FOOTWORK
So, how about ducks and geese that spend hours bobbing around in water barely above freezing temperature? They have waterproof plumage, but what keeps their legs and feet from becoming frostbitten and eventually gangrenous?
First, they reduce the circulation in their feet to a mere trickle in a network of blood capillaries. Just enough flows to keep the tissue cells alive. Second, through a special heat-exchange system, the arterial blood flowing to their feet heats up the cool venous blood returning to their body. All of this serves to keeps a water bird’s heat from being lost to the outside. Birds have another trick we humans can’t do. At night, especially in extremely cold weather, they can lower their body temperature a few degrees to conserve energy. When a bird becomes cold, it tenses its breast muscles and begins to shiver to generate body heat. Unlike us, they do this in an almost imperceptible manner.
C) CHANGING HABITS
Birds also adjust their behaviour to cope with cold. In really cold weather, land birds favour sheltered or wind-protected areas for feeding and roosting. Waterfowl often tuck their heads into their “armpits.” Some species, such as grouse, ptarmigan and even snow buntings, plunge into soft snow and use body heat to warm up their “cave.” On nights when temperatures are exceptionally frigid, some small birds will pack themselves into tree cavities. On one occasion, up to 50 titmice were found huddled in a ball-like mass in a cavity.
So don’t worry about the birds in winter. Nature has provided them with an array of adaptations. After all, if they couldn’t handle it, they wouldn't stay.