Nature Notes for January 31, 2014
Arctic temperatures, ice, wind chill, and blizzard
conditions have resulted in Environment Canada issuing many watches and
warnings this winter. We are admonished to stay indoors or leave no skin
exposed if we have to venture out. For most humans, this has been a winter to
stay close to the fire and read.
So just how do birds survive in these conditions?
Those that can’t tolerate the cold fly to warmer places for the winter. Others
have adapted to survive in frigid temperatures.
Birds are warm blooded creatures, with a slightly
higher body temperature than most mammals. They must maintain their temperature
or perish. They have several adaptations to help this.
First, they are covered with feathers. Feathers are
very good insulators. As cold temperatures approach, birds that stay for the
winter grow more feathers, much as a dog grows a denser coat of fur. The small,
down feathers which grow close to the skin are excellent insulators. People
stuff coats with the down feather of Eider ducks, collected from nests, to keep
themselves warm. Often, birds will fluff their feathers a bit, creating small
air pockets which add to the insulation.
Feathers are also waterproof, which prevents
heat-stealing moisture from penetrating to the skin.
Birds have what is essentially a heat exchanger in
their legs. The blood in the arteries going to the feet passes alongside the
incoming veins, passing the heat to the incoming blood and hence warming it. As
well, birds can restrict the amount of blood going to their feet, which also
reduces heat loss. Often the temperature of duck feet will be only just above
freezing, while the rest of the bird is very warm.
Sometimes you may see a bird standing on one foot,
with the other tucked up into the body feathers to keep it warm. Many birds sit
on their feet to warm them. The ducks in Cobourg Harbour often roost on the
shore with feet tucked up into their feathers.
Birds must eat a lot of high quality food to
maintain their body temperatures. The ice storm which occurred just before
Christmas would have been a great hardship for many birds, since their food was
unavailable, locked up in a coating of ice. Many birds probably did die,
although I have seen a few robins and waxwings, both fruit dependent in winter,
since the ice storm, so some survived.
Such species as Blue Jays and Black-cappedChickadees store a supply of seeds for the winter. I have watched Blue Jays
make many trips to acorn laden oak trees in the fall. They are storing the
acorns above the snow, in crevices in trees or even nooks in a building. My
backyard chickadees have many sunflower seeds stored in the cracks in the fence
of my backyard. The Gray Jay is well known for caching food, a necessity since
this species starts nesting while there is still snow on the ground.
At my backyard feeders, there is always a rush of
birds – Black-capped Chickadees and Mourning Doves mostly this year – first
thing in the morning. These birds feed furiously to replenish the energy that
they have expended overnight just to stay alive. After they have fed, they will
seek out a sheltered spot to roost and stay still.
In my garden, a favourite roost of the Mourning
Doves is the branches of the spruce tree. Depending on the direction of the
wind, the favoured roost may change a bit. If there is sun, the birds will be
in the sun, feathers puffed out, absorbing the solar warmth.
Birds use several techniques for overnight survival.
Night roosts are in sheltered places, out of the wind. Some species, such as
Ruffed Grouse and Snow Buntings, actually dive under the snow. The snow
provides insulation. Groups of cavity
nesting birds such as bluebirds, pile into a cavity or nest box. A number of
birds in a small space will keep all of them warmer. Chickadees have the
ability to reserve energy by putting themselves into hypothermia overnight and
pulling out it at daylight.
It
really is remarkable that such small animals can tolerate such cold
temperatures as we have had this winter. When the mercury drops to -30ºC, as it
has several times this winter, I fear that even I become an armchair birder,
enjoying the birds from the comfort of my house.
