Friday, May 18, 2012

They are what make a bird a bird

kw: book reviews, nonfiction, animals, birds, feathers, natural history

I suppose there are good reasons that it is a crime to possess a feather from any wild bird in the United States, but it is a shame. Birds shed feathers all the time, whether sparrow, swallow, robin, crow, hawk, owl or eagle. Whatever passes through or over your yard, leaves an occasional calling card, particularly during molting. Children (and many adults) delight in collecting fallen feathers.

I used to put a few feathers in the brim of my hat. Every year there would be new ones, and the colorful ones—blue jay or cardinal or swallow—make a great accent. I learned early on to first freeze a feather to kill mites and fleas. But in recent years, I don't wear wild bird feathers any more; it could land me in jail.

In a closing chapter of Feathers: The Evolution of a Natural Miracle, author Thor Hanson took an unusual feather he had found to the Smithsonian Feather Identification Laboratory. It was from a leg of a golden eagle. The lab curator did not return it to him; she is authorized to keep feathers of endangered birds, and he is not.

There is much to learn from the book. Feathers first evolved nearly 200 million years ago. Remnant molecules in Chinese dinosaur fossils showed that they were as brilliantly colored as modern birds. Yet feathers evolved only once, so they are a "hard feature", compared to eyes, which evolved independently at least four times, and flight itself, which evolved independently at least five times.

I was surprised to learn that feathers did not evolve from scales. Their development is so different that they cannot be related. I didn't fully understand the explanation of the way a feather grows, but the intricate on-and-off dance of keratin-producing cells is a spectacular, choreographed sequence. It is amazing that the process works at all, yet it produces thousands of feathers, on every bird's body, year after year. A natural miracle indeed!

A coat of feathers is no simple matter. When we look at a bird, we see the contour feathers that cover most of the body, the pinions or flight feathers on the trailing edges of the wings, a few tail feathers, and perhaps some downy bits poking out on the legs. Under the contour feathers a layer or more of down feathers provides the best thermal insulation known, by far. My 2.5-pound down sleeping bag has kept me warm in subzero campouts. If I wanted the same insulating value from a "fiberfill" type synthetic, I'd need at least eight pounds, and the bag would take up four times the space, even scrunched into a stuff bag.

How then does a bird keep from boiling over on a warm day? I can shed the sleeping bag easily, but the robin in my yard, who is equipped to sleep through a freezing night, must wear the same integument six months later when the temperature exceeds 90° F (32° C). Birds don't sweat! If needed, they pant, they hide in the shade, they splash in water, and they start out by being several degrees hotter than the average small mammal, so they are more likely to be radiating heat out to the environment, rather than receiving it.

When I finished reading the book, I thought, "Is this all?" The fifteen chapters cover numerous aspects of feathers, from their history and evolution to the sexual selection that has led to so many spectacular varieties, from their uses both industrial and fashionable to the many theories of how flight evolved, and most of all to the simple wonder of such surprisingly complex and beautiful objects. The author's passion shines through the writing, making the reading all the more enjoyable. From some writers, 300 pages is a lot. From Thor Hanson, it is just an appetizer!

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