By Sarah Wilson,
Healthy Planet Staff Writer
The recent deep freeze got me wondering how ducks can walk across ice or paddle in near-freezing water without a problem?
To understand this, we begin with the fact that according to the Phylogenetic system, birds are reptiles. This system sorts life by ancestry, not by how they look.Both birds and what we generally think of as reptiles sport two holes on each side of the skull, making them brethren.
Why does this matter for our question? Because of the skin on their legs. Duck legs are covered by something called “scutes.” Scutes (from Latin for shield) are thick and durable. When you think of Alligator hide, you’re thinking of scutes.
Not only are scutes amazingly rugged, protecting from cuts and scrapes, but they also hold in moisture. A bird’s leg is always dry, which explains why songbirds don’t stick to the metal perches on bird feeders in subzero temps.
For our duck question, those thick scutes minimize heat loss, too.
Under those scutes, a duck’s anatomy is the next clue. Unlike our limbs, which are packed with muscle and nerves, those skinny duck legs are mostly bone and sinew with few nerves. The muscles that do much of the work of the leg, the drumstick if I may, are covered in fat and then protected by warm down feathers.
But doesn’t the warm blood coming down from the body and the cold blood coming up from the feet cause massive heat loss for this bird? No. They have something called a rete mirabile (rough translation: wonderful net). Think avian heat exchange system. It’s a network of interwoven arteries and veins that moderate the blood temperature in both directions.
Warm blood, as it heads from the toasty body to the chilly foot, “meshes” with the cold blood in the veins heading from the chilly foot back to the toasty body. The temperature of both streams changes.
The warm body blood is cooled so the duck has less heat loss from their feet, and the cold foot blood is warmed so the duck’s body doesn’t have to expend energy doing that. The duck ends up with an unfrozen foot and a consistently warm body.
To sum up, because duck legs are covered with scutes, are made of little more than bone and sinew, have few nerves, and have an efficient heat exchange system, a duck can waddle across the ice without a problem.
Nature is amazing.