Wednesday, June 22, 2011

403. Avian Architecture

A cape weaver building its intricate nest
By Henry Fountain, The New York Times, June 20, 2011

I live in a nice clapboard house and work in a gleaming steel-and-glass skyscraper, but after reading “Avian Architecture: How Birds Design, Engineer and Build” I feel cheated. I’ll never get to enjoy the comforts of the nest of a long-tailed tit.

As Peter Goodfellow, the book’s author, points out, the dome-shaped nest is one of the most beautiful and skillful constructions in the animal kingdom. The average one contains a couple of hundred sprigs of moss and several thousand lichen flakes, woven together with purloined spider silk and lined with feathers. A nice place for a nap, if you are six inches long.

“It’s an amazing creation,” Mr. Goodfellow, who has had the pleasure of watching long-tailed tits nest in his garden in Plymouth, England, said in a telephone interview. “What’s doubly astonishing is that they use it just once.”
Mr. Goodfellow is a retired teacher of English language and literature and a lifelong bird-watcher, although he takes his bird-watching only so far. “I’ve never actually gotten into the work of the scientist, who might well watch for a whole day or week while a bird makes a nest,” he said. “I’ve never had that deep science bent that’s made me sit down to do that sort of thing. I enjoy the reading and the writing.”
He first had the idea to write about nests 35 years ago, and the result was a book called “Birds as Builders.” This time, Mr. Goodfellow adds “designer” and “engineer” to the job description, and that does not seem at all like a stretch.
Nest designs fit into about 10 broad categories, and “Avian Architecture” provides what it calls “case studies” of each, with photographs and detailed drawings of construction techniques.
There are minimalist approaches like scrape nests — the small depression that the piping plover makes on a beach, for example — and hole nests like those that the red-cockaded woodpecker, a species found in the southeastern United States, drills into pine trees. (The exuded sap coats the tree surface around the hole, trapping snakes and other potential predators.) Aquatic nests of grebes and other freshwater birds are only slightly more complex, often made just by piling up vegetation until it forms a floating mass. Mound nests, made on land, are also often simple piles of mud, leaves or rocks.
Far more elaborate are the familiar cup and dome nests, and the less familiar hanging nests, that grace trees worldwide. These are where birds’ engineering skills shine. The song thrush, for example, a common European bird, begins building her (in many species, the female does the work) cup nest with a foundation of sturdy twigs, then adds moss and dried grass to form a crude cup, which is lined with wood pulp and mud and decorated on the outside with moss and leaves for camouflage. The Baltimore oriole weaves its nest of plant fibers, vine strips and hair from two or more attachment points on a tree branch. And that long-tailed tit uses the spider silk in Velcro-like fashion, detaching it from the lichen and moss and then reattaching to expand the nest if it has a larger brood.
Those examples, and the many more included in “Avian Architecture,” make the book a good gift for anyone who has doubts about Darwin. While evolution is seldom mentioned explicitly, it pervades this book both in broad ways (the sheer diversity of nest types, even among related species) and in specific ways (camouflaged eggs in nests where they lie in view of predators; white eggs in nests where they are out of sight).
Brood-keeping is the reason for most nests’ existence. “It’s been created to be the family home,” Mr. Goodfellow said. “That’s true whether it’s just a scrape in the sand or the beautiful little feathery, mossy cup of the hummingbird.” In most cases they are not love nests; mating occurs elsewhere.
The elaborate structures built by bowerbirds are an exception. Mr. Goodfellow devotes a chapter to these fascinating birds, relatives of the catbirds, which are found in Australia and New Guinea. They build structures of grass or sticks on the ground, often aligned east to west, and decorate them with leaves, stones or other objects. In the case of the satin bowerbird, most of the objects are in shades of blue, and can include bits of plastic or ribbon.
The structures are unusual, as is the fact that it is the male that builds and decorates them. And unlike most birds, which seem to have an innate ability to build a perfect nest first time, every time, there is evidence that bowerbirds build better bowers as the years pass by.
Then again, as “Avian Architecture” points out, these bowers are not really nests at all. They are courtship displays, designed to signal to females that the builder would make a good mate.
And once the female makes her choice and mates with the male of her liking, what happens?
“She goes off and makes a proper little cup nest to raise the young,” Mr. Goodfellow said.

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