Friday, March 8, 2013

Let It Roll Off Your Back

When skies are grey and pouring rain, people will grab their raincoats and umbrellas before going outdoors.

Many wild animals will take cover under trees or in any dry space they can find because, as everyone knows, being out in the cold can be hard to bear, but being soaked to the skin along with being out in the cold is quite a bit worse. 
Blue Penguin, Christchurch NZ - Photo by Gay Schroer
Since this is very true for people and many animals, how come penguins can be seen in the Antarctic, swimming comfortably in the frigid waters, and then hopping out of the water onto the snow as if neither situation is very cold?

How about ducks and geese swimming in a pond on a cold winter’s evening, never seeming to be bothered by the chilling water? 
Tsavo, a Bateleur Eagle, shows off his beautiful head feathers (Photo by WBS volunteer Sandra Lowe Murray)
This is all possible because of the remarkable thing that only birds are lucky enough to posses—feathers!  Feathers have unique qualities that not only allow most birds to fly, but also to keep birds warm/cool and dry when necessary.
Parts of a feather: 1-Vane, 2-Rachis, 3-Barb, 4-Afterfeather, 5-Hollow Shaft, Calamus (Illustration from Wikipedia website) 
An extremely important component of feather waterproofing is the structure of the feathers themselves. The longest and thickest part of a feather is called a rachis.  From the rachis grow the barbs.  These barbs together form the vane or blade of the feather (the softer more pliable section).  Off of the barbs are smaller protrusions referred to as barbules. These are microscopic and have tiny hooks on them that connect the barbules together and by extension, the barbs themselves. When all of the barbules and barbs are hooked together (in a sort of “Velcro” fashion) this creates touch points on the feather that makes the water bead, and keeps water from seeping into the feather itself.
Note how this Barn Owl's feathers overlap, like shingles on a roof
Since bird feathers have the ability to repel water, slightly overlapping feathers across the body makes feathers act like roof shingles so that the water can roll down each feather and then off the bird.  Birds also have a gland at the base of their tails that secretes oil.  Through preening, the oil is spread over all feathers and aids in keeping birds waterproof.
Jet, an American Kestrel can control his body temperature by raising or lowering his feathers (Photo by Gay Schroer)
There is a big difference between uropygial gland oil and fossil fuel oil.  Oil spills will separate the feathers and cause gaps in the arrangement of them.  This allows water and cool/hot temperatures to reach their down feathers (fluffy feathers that generally lie below the contour feathers) and also their skin. In addition to the lack of waterproofing, the oil-covered birds will try to preen (run feathers through their beak) continuously to rid their feathers of the oil.  Not only will the bird swallow oil, constant and non-stop preening is called hyper-preening and can result in permanent feather damage (broken rachises, barbs and barbules).
Oiled Bird (photo from the Wikipedia website)
Some bird species like pigeons and herons have types of feathers called powder down. Instead of molting, powder down feathers continuously grow and the barbs break down into a fine powder which is spread throughout the rest of the feathers.  This powder is believed to help repel water from some bird’s feathers.
Some birds, such as this Great Blue Heron have powder down (Photo by Gay Schroer)
While all of the above tactics aid in keeping water off of a bird’s feathers, Sand Grouse that live primarily in the desert have feathers that capture water.  These feathers are curved and are able to keep water trapped so that, after it bathes in water (which can be miles from its nest), it can then carry the caught water back to its chicks, which drink the water from their parents’ feathers. 

So whether or not they are keeping dry or carrying water with them, something as light as a feather, is heavy with importance for a bird’s survival.

The next time you visit the World Bird Sanctuary be sure to check out the “touch table” display to see just how remarkable a feather truly is.

Submitted by Teresa Aldrich, World Bird Sanctuary Naturalist/Trainer 

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