Sunday, January 23, 2011
How Do Birds Survive the Cold?
I checked the thermometer before I went outside to fill the feeders this morning. -16º F.
I bundled up - hat, coat, boots and gloves. But it just wasn't enough. In a matter of minutes, I felt the cold biting at my fingers and nostrils.
My breath froze on my eyeglasses. By the time I filled the 6 feeders, my fingers were numb. And I could feel the ice clinging to the tiny hairs inside my nose.
The birds outside didn't look much better. They all had frost around their faces too.
How do these creatures survive temperatures like this?
The answers have to do with feathers and behavior, anatomy and physiology.
Songbirds need to maintain an average body temperature of ~104º F. On really cold days, they fluff out their feathers to trap body heat, creating a thermal barrier against the cold. That's what they were doing this morning. All the birds at my feeders were fluffed out like cute little plush toys - almost as wide as long.
Birds feeding on the ground - the juncos, Tree Sparrows and cardinals - fed while squatting down so their feathers covered their legs and feet. One of the cardinals shivered (to increase his body temperature) as he pecked at cracked corn. A Blue Jay up in the spruce tree near my feeders, squatted on a limb, fluffed out its feathers to cover its feet and turned its body towards the sun. Then the jay buried his beak under his wing.
Yes, beaks play a significant role in avian thermoregulation. Beak size matters. In warm climates, large beaks help birds dissipate heat. Smaller beak size (in relation to body size) in colder climates helps birds reduce heat loss.
But what about plumage color? Why do so many of the birds at my feeders have white plumage on their bellies and black feathers on their backs?
Dark feathers assist with thermo-regulation. The dark pigments absorb heat from the sun (like a black car sitting in a parking lot in the summer). The "white" feathers provide additional insulation - holding in the heat generated by the bird's metabolism.
What makes white feathers "warmer" than others? They're structurally different. The "white" feathers are created due to an absence of pigments in the cells. The spaces where the pigments would be are "empty" of pigments but full of air. The bubbles of air - like the air spaces in downy feathers - trap body heat, increasing the feather's insulating capability.
Cardinals don't fit this black & white plumage theory. But they're originally "southern" birds. They've extended their range north with the increased number of people feeding birds in the winter.
For more information on how birds survive the cold, check out this website
Posted by hvhughes at 12:53 PM