01/31/2019
Story and photo by Gabrielle L. Wheeler
Last week I wrote about tundra swans floating at the southern tip of Keuka Lake in Hammondsport. My encounter with these winter waterfowl has gotten me thinking. How is a bird able to sit in frigid water and not get hypothermia? The answer to that question is simply complex and has much to do with two different things: feathers and blood flow.
All birds have feathers but not all feathers are created equally, nor do all birds wear the same number of like feathers. This makes sense, of course. The hair (and skin) of cattle that originate from hot locations, such as Brahman cattle of India, is different from those originating in colder locations, such as highland cattle of Scotland. Thus, waterfowl that spend winter months in colder locations have more feathers that keep them warm in sub-zero temperatures. There is a reason down feathers are used in winter jackets and that is because the contour of these feathers allows them to hold a little pocket of warm air within the plumy wisps. Waterfowl and all non-migratory birds make use of a thick layer of down feathers that keep warm air close to the skin.
Waterfowl (and most other kinds of birds) also have a gland at the base of the tail, the uropygial gland, that produces oil that is spread on feathers and makes them waterproof. In order to repel the frigid waters of a winter lake, ducks and other waterfowl must spend much time preening to keep feathers freshly oiled. Water-repelling feathers keep cold water off dry skin that, if exposed, would quickly lead to hypothermia. Thus, between the waterproofing and an insulation of warm downy feathers, the birds are primed to make it through the winter.
However, there is one other question: Why don’t waterfowl get frostbite on their bare feet? This is attained through a counter-current heat exchange system. In this system, the blood coming into the feet loses its heat to the blood going back up into the body. In this way, the blood that goes into the feet is already cooled and that heat does not get lost to the environment. It also prevents cold blood from circulating back into the body, which would lower the core body temperature.
While these adaptations to help waterfowl survive cold temperatures are impressive, it is important to note that it doesn’t work like an on/off switch. Birds acclimate over the course of the winter, and a bird can suffer from hypothermia and frostbite if not given time to adjust.
