Bowerbird
From The Art and Popular Culture Encyclopedia
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Bowerbirds make up the bird family Ptilonorhynchidae. The family has 20 species in eight genera. These are medium to large-sized passerines. Their diet consists mainly of fruit but may also include insects (especially for nestlings), flowers, nectar and leaves in some species.
The most notable characteristic of bowerbirds is their extraordinarily complex courtship and mating behaviour, where males build a bower to attract mates. There are two main types of bowers. One clade of bowerbirds build so-called maypole bowers, which are constructed by placing sticks around a sapling; in some species, these bowers have a hut-like roof. The other major bowerbuilding clade builds an avenue type-bower made of two walls of vertically placed sticks. In and around the bower, the male places a variety of brightly colored objects he has collected. These objects — usually different among each species — may include hundreds of shells, leaves, flowers, feathers, stones, berries, and even discarded plastic items, coins, nails, rifle shells, or pieces of glass. The males spend hours arranging this collection. Bowers within a species share a general form but do show significant variation, and the collection of objects reflects the biases of males of each species and its ability to procure items from the habitat, often stealing them from neighboring bowers. Several studies of different species have shown that colors of decorations males use on their bowers match the preferences of females.
Uy and collaborators have shown that mate-searching females commonly visit multiple bowers, often returning to the male several times, watching his elaborate courtship displays and inspecting the quality of the bower and tasting the paint the male has placed on the bower walls. Many females end up selecting the same male, and many under-performing males are left without copulations. Females mated with top-mating males tend to return to the male the next year and search less.
Gilliard has suggested the "transfer effect", in which he claimed that bowerbird species that build the most elaborate bowers are dull in color and show little variation between male and female, whereas in bowerbird species with less elaborate bowers, the males have bright plumage. This hypothesis is not well supported because species with vastly different bower types have similar plumage. Borgia has suggested that the bower functioned initially as a device that benefits females by protecting them from forced copulations and thus giving them enhanced opportunity to choose males and benefits males by enhancing female willingness to visit the bower. Evidence supporting this hypothesis comes from observations of Archbold's bowerbirds that have no true bower and have greatly modified their courtship so that the male is limited in his ability to mount the female without her cooperation. In toothbilled bowerbirds that have no bowers, males may capture females out of the air and forcibly copulate with them. Once this initial function was established, bowers were then co-opted by females for other functions such as use in assessing males based on the quality of bower construction. Recent studies with robot female bowerbirds by Patricelli and collaborators have shown that males react to female signals of discomfort during courtship by reducing the intensity of their potentially threatening courtship. Coleman and colleagues found that young females tend to be more easily threatened by intense male courtship, and these females tend to choose males based on traits not dependent on male courtship intensity. The high degree of effort directed at mate choice by females and the large skews in mating success directed at males with quality displays suggests that females gain important benefits from mate choice. Since males have no role in parental care and give nothing to females except sperm, it is suggested that females gain genetic benefits from their mate choice, but this has not been established, in part, because of the difficulty of following offspring performance because males take seven years to reach sexual maturity.
This complex mating behaviour, with its highly valued types and colors of decorations, has led some researchers to regard the bowerbirds as among the most behaviorally complex species of bird. It also provides some of the most compelling evidence that the extended phenotype of a species can play a role in sexual selection and indeed act as a powerful mechanism to shape its evolution, as seems to be the case for humans.
In addition, many species of bowerbird are superb vocal mimics. Macgregor's Bowerbird, for example, has been observed imitating pigs, waterfalls, and human chatter. Satin Bowerbirds commonly mimic other local species as part of their courtship display.
Bowerbirds have also been observed creating optical illusions in their bowers to appeal to mates. They arrange objects in the bower's court area from smallest to largest, creating a forced perspective which holds the attention of the female for longer. Males with objects arranged in a way that have a strong optical illusion are likely to have higher mating success.
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