Biology Reference
In-Depth Information
On cold nights, roosting chickadees “turn their thermostat down” by allowing their
body temperature, normally above 100°F (38°C), to drop to as low as 82° (28°C). This
saves energy, just as we do when we turn down the thermostat in our house or apartment.
Whenachickadeeawakensonacoldwintermorning,itimmediatelystartstoshiver.That
muscle activity quickly raises its body temperature back to normal.
Another strategy that some species use to survive long winter nights in the far north is
to cozy up to one another. Chickadees don't do this — each one sleeps in its own cavity
— but bluebirds, creepers, and Pygmy Nuthatches sometimes do.
Redpolls have more rods in their retinas than do many songbirds, allowing them to see
better in dim light. They start feeding before dawn and continue to eat voraciously after
sunset. They also have well-developed pouches along their esophagus, allowing them to
load up on seeds at day's end so they can stoke the metabolic fires through the night.
Q Why don't birds get cold feet?
A
Actually, songbirds do get very cold feet: the surface temperature of their toes may be
barely above freezing even as the bird maintains its core body temperature above 100°F
(38°C). But most birds don't succumb to frostbite because there is so little fluid in the
cells of their feet, and because their circulation is so fast that blood doesn't remain in the
feet long enough to freeze.
Wedon'tknowifcoldfeetbotherbirds.Wedoknowthattheyhavefewpainreceptors
in their feet, and the circulation in their legs and feet is a double-shunt — the blood ves-
sels going to and from the feet are very close together, so blood flowing back to the body
is warmed by blood flowing to the feet. The newly cooled blood in the feet lowers heat
loss from the feet, and the warmed blood flowing back into the body prevents the bird
from becoming chilled.
