Apprentice Behavior In Bower Birds

The family includes species with socially monogamous and polygynous mating systems. Monogamous pairs of catbirds defend an all-purpose territory. Males do not assist with nest building, incubation, or brooding of nestlings (which they do feed). The promiscuous males of the 17 polygynous bowerbirds defend only the immediate area of their bowers. A seasonal hyperabundance of fruits permits promiscuous males to spend inordinate amounts of time at their courts, in attracting/ courting females, while also permitting females to nest and provision their offspring unaided.

Uniquely within the avian world, promiscuous males clear court areas and skillfully build complex symmetrical structures of sticks, grasses, or other vegetation, and decorate them. Three types of modified courts are: cleared and leaf-decorated courts, maypole bowers, and avenue bowers. Maypoles consist of branches and/or saplings with accumulations of orchid stems or sticks and an elaborate and decorated discrete mat beneath it. Avenues consist of two parallel walls of sticks or grass stems placed vertically into a foundation that is laid on a ground court that may extend beyond one or both ends of the bower to form a platform.

Male bowerbirds decorate courts and bowers with items such as leaves, flowers, fruits, lichens, beetle wing cases, insect skeletons, tree resin, snail shells, bones, river-worn pebbles, and specific parrot tail feathers and nuptial plumes of adult males of certain birds of paradise. Charcoal, glass, and innumerable other man-made objects may also be used. Males of some species manufacture and apply paint to bowers, even holding a wad of vegetable matter in the bill tip to use as a tool to apply paint. Because of this complex behavior, bower-birds have been associated with high intelligence and artistic abilities.

Courts and bowers are located on favored topography exhibiting one or more micro-environmental features required by males. Bower sites are occupied for decades, and adult males exhibit long-term (one or more decades) fidelity to them. Immature males spend an apprenticeship of five to six years visiting rudimentary, or practice, courts or bowers of their own construction and bowers of adult males to acquire skills for better bower building, decorating, and displaying to attract females.

Courts and bowers are critical to male reproductive success in the polygynous species. They provide a focal point to which males attract females for courting and mating. Adult males of most species average 50-70% of daylight at their bower sites. Activities at bower sites involve vocalizations (advertisement song and other calls, including mimicry), bower maintenance (building, decorating, painting), display, and chasing unwanted conspecifics away. Rival males damage each others bowers and/or steal favored decorations, in so doing improving their own chances of attracting more potential mates.

Male satin bowerbird (Ptilonorhynchus violaceus) in its bower (Australia). (Photo by Tom McHugh. Photo Researchers, Inc. Reproduced by permission.)

Sexual selection, through mate choice by females, is fundamentally important to the evolution of elaborate display traits (ornate plumage and/or bower complexity/decoration) of bowerbirds. In some species colorful and elaborate display plumage has been lost and replaced by, or transferred to, a bower structure and its decorations. Discerning females assess the frequency and intensity of male bower attendance, the quality and/or quantity of bowers and decorations, displays, plumage, and vocalizations before soliciting the male of their choice. It is the older males, those with greater experience, skills, and survival, that are typically selected as mates by females.

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