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Who Needs Wet Suits With Feathers Like These?

Two Types of Feather

Photo: Woody Hagge

A loon's body feathers are two main types: contour feathers and down feathers. Down feathers are soft, fluffy gray feathers that insulate a loon's body to hold its heat inside. These are like the stuffing in a human's down jacket, or a nice thick sweater. The best thing about down is the insulation it provides. But you wouldn't want to face a rainstorm in just a sweater! Like a warm sweater, the worst thing about down is how absorbent it is. Down quickly gets soaked and mats together when wet. So not only do loons have to keep their skin dry, but also keep all of their down feathers dry. They can do this thanks to their outer contour feathers. These feathers cover every millimeter of down and skin, working like a perfect rain suit, or a diver's dry suit.

Contour feathers take their name from the fact that they give loon bodies their shape, or contour. Loon contour feathers are beautifully patterned black and white. The white parts of the neck feathers are longer than the black, giving a loon's neck the texture of exquisite velvet corduroy. Contour feathers are designed to keep the body inside nice and dry. Water molecules are attracted to other water molecules, and that's why water forms droplets rather than sheeting away on most surfaces. Contour feathers are so tightly fitted together that drops of water can't squeeze between. To help even more, loons have an oil gland on the base of their tail. It looks like a funny pimple, and when they squeeze it or rub it with their bill, small amounts of oil come out, which they wipe on their outer feathers to make them more waterproof.

But No Feathers Here!
Although the loon's skin is protected by down and contour feathers, its beak, eyes, legs, and feet are bare. So how does a loon keep those body parts warm in frigid waters? The loon's beak is made of the same kind of tissue as our fingernails, without a blood supply that could get cooled by the air and then travel to the rest of the loon's body. No matter how cold the beak gets, the rest of the loon can stay warm. The legs and feet have a much smaller blood flow than our legs and feet, but still need enough blood to power the muscles that help it swim. Blood flowing from the cold feet back up into the warm body gets heated before it reaches the body because it travels in vessels right next to the hot blood traveling down to the feet from the body. This is called a "double shunt system."

That still leaves a loon's eyes. Loon eyes don't turn nearly as much as ours do, so their eyelids don't expose as much of their eyes. That's why you don't see more than the iris and pupil on a bird's eye. Minimizing the exposed part of the eye helps prevent it from drying out when a bird is flying, and from losing too much body heat. And for even more help, birds have an inner eyelid called the nictitating membrane. Birds can swim or fly with this inner eyelid closed part of the time and still see because the membrane is transparent.

How Many Feathers In All?
Are you curious about how many feathers a loon has on its body? "Back in 1936 and 1949," says bird expert Laura Erickson, "two ornithologists actually counted every contour feather on several birds. The smallest number was on the Ruby-throated Hummingbird, who had 940. The most was on a Tundra Swan, with 25,216. We don't know of anyone who counted all the feathers on a loon, but we'd guess they have somewhere between 18,000 and 20,000."

 

 
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