Fluffy feathers for winter warmth
Winter poses several challenges for birds. Scarce food supplies and limited water are just a few obvious challenges to winter survival for nearly all birds. Extremely cold temperatures, strong winds, driving snow, and freezing rain are another set of problems that birds must overcome. Add to this long and dark nights that seem to go on forever can be deadly for birds. So, just how do birds survive the rigors of winter?
As you can imagine, birds have many adaptations to help survive extreme winter weather. One of these adaptations is more common than you think. Feathers are the first and best line of defense, and are critical to a bird’s survival. But what do you really know about a birds feathers?
Many of our wintering birds, such as the American goldfinch and black-capped chickadee, add additional feathers in preparation for winter. A goldfinch or chickadee is coved with approximately 1,100 feathers during summer, but increases to over 2,500 in winter. That is about a 45 percent increase in feather density. However, if you look at the bird, it really doesn’t look like it has so many more feathers. That is because the outer contour feathers overlap each other and lay flat. The other increase in feathers are in small, fluffy down feathers, which occur under the outer feathers, so you won’t see these at all.
Not only do birds that live in cold climates have more feathers than birds in warm climates, aquatic birds, such as ducks and geese, have more feathers than terrestrial species of a similar size. Undoubtedly, this is due to the rapid loss of heat when a bird is exposed to water.
To demonstrate just how important feathers are for birds, all you need to do is look at how much feathers weigh. This might be a little confusing at first, but listen to this. For a bird to fly, they need to be as lightweight as possible. So, nearly every part of a bird’s body is modified to make it as lightweight as possible. For example, birds don’t have teeth because a full set of teeth are very heavy. Instead, they have a lightweight bill or beak. Birds also have mostly hollow bones, as opposed to solid bones, which are extremely heavy. So…. feathers need to be light. Who hasn’t heard of the saying “light as a feather?" Individual feathers are light, but when you put all the feathers together, they have considerable weight. In fact, in most bird species, the feathers are usually two to three times heavier than the bird’s entire skeletal system.
Obviously, feathers keep the birds warm. During very cold days, and nights, birds fluff up their feathers, reducing the amount of heat loss by up to 30 percent, compared to when their feathers are not fluffed up.
Bird feathers also help keep birds dry in wet weather. We have always thought that a bird expresses oil from a gland near the base of their tail, called the urpygial gland, to make their feathers waterproof. Turns out this isn’t totally correct. While the oil might help with water repellent, it’s not essential. The micro-structure of the feather's barbs and barbules, which make up the feather, provide evenly-spaced ridges with narrow gaps that shed water quickly and efficiently, giving the feather the waterproofness without the oil. The oil is there to keep the feather lubricated and from becoming brittle and breaking prematurely. As you can see, there is more to a bird’s feather than meets the eye. Until next time…
Stan Tekiela is an author / naturalist and wildlife photographer who travels the U.S. to study and capture images of wildlife. He can be followed on www.facebook.com and twitter.com. He can be contacted via his web page at www.naturesmart.com.