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Say it with bowers: if male bowerbirds build it, females will come. But in the mountains of New Guinea, one species is sending mixed messages
Natural History, March, 2002 by J. Albert C. Uy
The first Westerners to penetrate the rugged interior of New Guinea encountered a world of plants and animals new to them. One of the earliest European naturalists to explore the inland mountains was Odoardo Beccari, who set out in 1872 to climb the Arfak range in a northwestern peninsula of the island. Before his ascent, Beccari had heard stories of a small mountain bird with prodigious architectural talents, and in the Arfaks he found both the bird and its structures. They proved to live up to the rumors.
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Now known as the Vogelkop bowerbird, this uniformly brown creature was scientifically christened Amblyornis inornatus, its species name taken from the Latin for "unadorned." Its behavior, however, is reflected in the name used by local New Guineans: burung pintar, or "clever bird." It was this reputation that first led me to New Guinea to study the Vogelkops. In 1994, along with my then doctoral advisor, Gerald Borgia, a biologist who had already spent more than twenty years studying various bowerbirds, I climbed up the Arfak slopes.
Found only on the large island of New Guinea and in Australia, bowerbirds comprise nineteen species. Males of all but three species are polygynous, meaning that they try to mate with as many females as possible. In some species, one male can mate with as many as twenty females in a single season, while the majority fail to mate at all. Of the polygynous species, fourteen have the peculiar habit of building ground-based structures, called bowers, solely to attract the opposite sex. Bower design and decoration are specific to each kind of bowerbird. For example, the satin bowerbird, which inhabits the dry woodlands of eastern Australia, erects two parallel walls of sticks on top of a circular platform, also made of sticks. The walls flank a path that visiting females step onto. Adorning the platform in front of the path are objects such as assorted blue parrot feathers, white snail shells, and yellow and purple blossoms from wild tobacco. Other species of bowerbirds build towers; some simply clear leaf litter from the ground to form a court where the male dances for visiting females. In their own way, most bowerbirds are skilled architects, but none can rival the plain brown Vogelkop.
A male Vogelkop selects a forest sapling and tightly weaves sticks around it, shaping a conical hut that can reach six feet in width and four feet in height. Huts typically have a single doorway, neatly trimmed to form a perfect arch, which opens out onto a thick carpet of moss up to six feet square, also laid by the industrious male. On this mossy stage, the male displays thousands of objects he has collected from the surrounding forest, including orange rhododendron flowers, yellow leaves, blue fruits, red ginger berries, iridescent blue beetle carapaces, shiny fungi, and feathers from other birds, such as birds of paradise. (At one site we studied, a male pilfered a strip of blue tarp from our camp and laid it under his doorway; another stole a pair of knee-high green socks with bright yellow stripes.) Males arrange these objects according to color and size and promptly remove any that decay. In fact, the best way to coerce a male to come down from the forest canopy and onto his bower is to mix up his decorations. He quickly returns and puts everything back in order, sometimes in the presence of a surprised spectator.
The dimensions of a Vogelkop bower are even more impressive given the size of the builder. Weighing less than five and a half ounces, a Vogelkop male is not much bigger than an American robin. Great time and energy are thus invested in constructing and maintaining the relatively colossal bowers, illustrating the lengths to which the birds go to attract females. The bower is not used as a roost or a nest site. Females, which usually mate with only one male in a season, rear their young on their own, building simple bowl-shaped nests six inches in diameter and six to ten feet up in a tree.
Hut-building Vogelkops inhabit New Guinea's Tamrau and Wandammen Mountains as well as the Arfak range. In 1981 physiologist Jared Diamond, of the University of California, Los Angeles, found an isolated population of Vogelkop bowerbirds in the Kumawa Mountains, about 100 miles south of the Arfaks. The Vogelkops of Kumawa (and the adjacent Fakfak range) construct strikingly different bowers. Instead of elaborate huts, these birds erect five-foot-high, spindly spires. Made of sticks loosely interwoven around a sapling, the spire resembles a dry Christmas tree. At the base of the spire, the male neatly lays a circular carpet, usually of black moss. The decorations are spartan, consisting exclusively of drab objects such as brown bamboo bark, black seedpods, and brown snail shells, all arranged by color and type near the carpet's perimeter. Given their distinct bower styles and color preferences, and the species-specific character of most bowers, one might guess that spire builders and hut builders are two kinds of bowerbirds. Yet they are physically identical and are classified as the same species.
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