the bowerbird and art -- 7/10/19
Today's selection -- from The Elephant in the Brain by Kevin Simler and Robin Hanson. The bowerbird is one of the most astonishing creatures on the planet:
"Bowerbirds are a family of 20 species scattered across the forests and shrub lands of Australia and New Guinea. What's distinctive about these birds are their eponymous bowers -- the elaborate structures built by the males of the species to attract females. Different species build their bowers in different shapes and sizes. Some are long avenue-like walkways flanked by walls of vertically placed sticks. Others are more like a maypole, circular structures propped up against a small sapling. Perhaps most impressive are the expansive gazebo-like bowers built by the humble (10-inch long) Vogelkop bowerbird. These structures tower up to nine feet off the ground, with an opening large enough (as Miller puts it) 'for David Attenborough to crawl inside.' The zoologists who first encountered these structures couldn't believe they'd been built by such a tiny bird, assuming instead that the local villagers had built them for their children to play in.
"As if these architectural feats weren't impressive enough, the male bowerbird takes the incredible further step of decorating his bower. This is where the parallels to human art become especially pronounced. Some species daub the walls of their bowers with a blueish 'paint' that they regurgitate through their beaks. Others amass large collections of rare and visually fascinating objects -- round pebbles, snail shells, flower petals, shiny beetles -- and spend hours arranging them meticulously around their bowers. Satin bowerbirds have a preference for blue objects: feathers, berries, flowers, and even industrial artifacts like bottle caps and ballpoint pens.
"These bowers serve only a single purpose: they're built by the males to attract females. Crucially, they aren't used by the females for laying eggs and raising young. After mating with a male, the female flies off to build her own (much smaller) cup-shaped nest up in a tree, and she raises her chicks entirely on her own, without any help from her mate.
|Two males displaying to a female masked bowerbird, Sericulus aureus, illustrated by John Gould(1804–1881)|
"From the perspective of the female, then, the male bowerbird exists only to provide his half of the genome. This may seem like a waste. Why doesn't he help raise his chicks, like the males of so many other bird species? But in fact, the bowerbird male provides more than just cheap sperm; crucially, he provides battle-tested sperm. Sperm that comes with a seal of approval from Mother Nature, certifying that the male in question is physically and (by implication) genetically fit. To construct and decorate a bower, a male must spend most of his free time scouring the forest for materials and arranging them meticulously into place. When his ornaments fade, he must collect new ones. He also needs to defend his bower against attack by his rivals, who are keen to sabotage his structure and steal his more impressive ornaments. 'During the breeding season,' writes Miller, 'males spend virtually all day, every day, building and maintaining their bowers.' The reward for all this effort is more mating opportunities. A successful male bowerbird can mate with as many as 30 females in a single mating season. The flip side, of course, is that some males with less-impressive bowers don't attract any females, and as a result their inferior genes don't get passed along to the next generation.
"It's instructive to consider this behavior from the perspective of both males and females. The male illustrates the virtue of the handicap principle. Bower-building is difficult, but that's precisely the point. If it were easy, every male could do it; fit males demonstrate their fitness only by doing things that unfit males can't do. Take the satin bowerbird, for instance. By focusing his collecting efforts on blue ornaments, which are exceedingly rare in nature, a satin male can prove his fitness more reliably than by using ornaments of any other color. Even a sickly male could decorate his hut with green or brown, colors that abound in the forest, but only the heartiest males can find enough blue to impress their potential mates. They collect blue objects not in spite of the difficulty, but because of it.
"Female bowerbirds, in turn, illustrate the importance of discernment in evaluating the displays of their male suitors. A female bowerbird will visit up to eight males before choosing her favorite to mate with. If she didn't shop around, she might inadvertently decide to mate with a less-fit male. This is especially important considering that environments can vary. If a satin bowerbird population happens to live in a forest with an abundance of blue-colored objects, even a relatively unfit male might be able to muster a display that would be impressive in a blue-scarce environment. It's only by shopping around for the most impressive displays that the female can ensure she's mating with the fittest male.
"There are intriguing parallels between bowerbird behavior and human art."