Thursday, June 16, 2011

Feathers: The Evolution of a Natural Miracle by Thor Hanson

(Note: The bird photographs in this blog posting were taken by me, are copyrighted by me, and can only be re-used with my permission.)

Feathers: The Evolution of a Natural Miracle
Feathers:  The Evolution of a Natural Miracle, by Thor Hanson

"The true mystery of the world," Oscar Wilde said (sounding, unintentionally I'm sure, like a Zen teacher), "is the visible, not the invisible."  I think about that idea almost every time I watch birds.  A chickadee starts in a bush on the front edge of my yard, darts skyward, and then flies straight through the middle of the cherry tree -- through the close set branches, the thick spring leaves -- and out the other side.  It's something we see every day.  In fact, all too often, it's something we don't see at all.

And yet, it's a miracle.

Black-capped Chickadee

Forget, for a moment, the wonder of flight itself.  Think simply about what it takes for the chickadee to fly at full speed through that tree.  The precision control to fly through such tight spaces, avoiding all obstacles.  The speed with which eye and brain must process information, even in flickering, constantly changing light.  It's a feat that should take our breath away in awe.  Every time.

And the magic of birds is closely tied up with the secrets of their most distinctive feature:  feathers.  Most of us don't spend a lot of time thinking about feathers apart from the birds themselves, but Thor Hanson, a conservation biologist and author (his previous book was The Impenetrable Forest: My Gorilla Years in Uganda) has.  And the result is his new book Feathers: The Evolution of a Natural Miracle.  At the  risk of overusing the word, I have to say that the book itself is a kind of miracle too:  an enjoyable, well written popular science book that is not only neck deep in real, hands-on science -- from chemistry to evolutionary biology to acoustics and paleontology -- but also manages to take us to the quirky, off-beat places where the human fascination with feathers lives.  It's a delightful trip, and if I wanted I could probably write an easy, intriguing review just by listing some of the fascinating nuggets you'll stumble across in this book.  I'll try to resist that impulse.

Bird feathers can create color in two different ways, by pigment and by structural properties that effect the refraction of light.  Much of the vibrant blue of a Steller's Jay's color, for instance, is due to the refractory properties of the feathers, not just to pigment.

Hanson begins where all things in biology begin -- with evolution.  In 1861 a quarryman in Germany uncovered what would become one of the most famous fossils in the world  -- the ancient winged creature that scientists named Archaeopteryx.  When that fossil made its way to England, it sparked one of the most heated debates in the history of science.  On one side, Sir Richard Owen, Director of the natural history at the British Museum, the man who coined the word "dinosaur" and a staunch believer "species were created and altered only by the hand of God."  On the other was "Darwin's bulldog" Thomas HuxleyOn the Origin of the Species was only two years old, and the debate over evolution was front page news.  Owen flatly denied that  Archaeopteryx was any kind of intermediate step, claiming that it was "simply the earliest known example of a fully formed bird."  But Huxley was not convinced.  He undertook an ambitious study of avian anatomy, and answered Owen with a series of papers and lectures that showed Archaeopteryx similarities to both birds and reptiles.  "But he went further," Hanson writes, "identifying a small dinosaur ... Compsognathus longipes that resembled Archaeopteryx in everything but the feathers .... "  There at the very beginning of the debate, Huxley laid out the basis for what most scientists now believe is the inescapable conclusion -- birds are the descendants of dinosaurs, and specifically, of a class of bipedal dinosaurs called Theropods.

But the debate goes on.

A young Cooper's Hawk.
Hanson introduces us to Dr. Richard Prum, whose theory of the development of feathers, derived from his knowledge of how feathers grow, has become the framework for modern ideas of feather evolution. To Xing Xu, a Chinese paleontologist who has uncovered some of the most important links in the story of birds (and feathers):  Sinosauropteryx prima, the first fossil that showed, definitively, evidence of proto-feathers (dinofuzz) -- Caudipteryx zoui, also a theropod dinosaur, but with distinctive feathered hands and tail -- and many more.  And we meet the dissenters, like Alan Feducia, a professor at the University of North Carolina, the de-facto leader of an increasingly marginalized group who call themselves BAND (Birds are Not Dinosaurs).

Tiny songbirds, like these bushtits, are constantly faced with the dual challenges of staying warm and staying cool. 

But evolution is only part of the story.  Just as fascinating are feathers as they exist today, in all their diversity and wonder.  From insulating down to sensitive facial feathers that can read air currents with amazing accuracy to aerodynamic flight feathers as sophisticated as anything humans have designed.  Feathers are the most efficient insulating material in the natural world, far outstripping the abilities of skin, hair or scales.  For instance, a Golden Crown Kinglet, Hanson tells us, one of the smallest of songbirds, can survive in places where night time temperatures get as low as 17 degrees below zero (-27 C), and devotes the vast majority of its feathers (7 percent of its body weight) to insulation.  "The difference between the outdoor air temperature and the cozy space inside a kinglet's feather coat could be as large as an astonishing 140 degrees (Fahrenheit)  ...."  He goes on to note that hundreds of bird species live at least part of the year above the Arctic Circle, that Penguins incubate their eggs unprotected in the middle of the Antarctic winter, and that the Bar-Headed Goose flies over thirty thousand feet high in its migration over the Himalayas.  "At that altitude, the air temperatures and wind chill often combine to dip below -80 degrees Fahrenheit ... Like Kinglets, these birds rely on feathers to insulate their bodies against the elements."

There is much more to Hanson's book, and I can't possibly go into everything.  (The flip-side of feathers' insulating power is that birds, whose metabolic rates are much higher than mammals, have had to develop elaborate cooling systems to keep from overheating.)  He also shows us some of the ways humans have co-opted bird's feathers -- from fashion to the design of airplane wings to quill pens.

Feathers  is a book almost any bird person will love. 

Check out my most recent posting Newcomers:  Birds of Spring at our sister blog, Birdland West.

You can read more about the evolution of feathers in the recent National Geographic Article, here.

1 comment:

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