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Ornithological Science
Abstract
Abstract
Bowers are display structures built by male bowerbirds (Ptilonorhynchidae) to court females. Avenue bowers consist of two parallel walls of upright sticks. Visiting females enter the avenue between the walls to watch the male displaying on a platform at either end of the bower. According to the “Optimal Illumination” hypothesis, bowers are oriented to optimise the amount of sunlight falling on the displaying male and the decorations on the platform. We studied bower orientation and platform utilisation at bowers of the western race of the Great Bowerbird, Chlamydera nuchalis nuchalis, near Darwin, Northern Territory, Australia. Most bowers were oriented in a NNE-SSW direction, in contrast to the prevailing NNW-SSE pattern observed in the eastern race, C. n. orientalis, in north Queensland. The disparity between these study populations in bower orientation appears to be related to their geographic latitudes and, consequently, azimuth of the sun during the peak morning display period. Males displayed on the platform that received the most sunlight. Moreover, mating success at east-facing bowers was higher than at west-facing bowers. These findings support the “Optimal Illumination hypothesis”. This is the first report demonstrating that bower orientation influences mating success based on quantitative data in avenue bower building species.
We are very grateful to R. Luxton for his hospitality and unrestricted access to his property, Coomalie Farm. We thank K. Ueda, M. Takagi, N. Yamaguchi, O. Mikami, K. Mikami, S. Mori, Y. Hayashi and members of the Laboratory of Ecology, Department of Biology, Faculty of Sciences, Kyushu University and the Laboratory of Animal Ecology, Department of Life Sciences, Rikkyo University for their field assistance and valuable suggestions. E. Kasuya helped us with the statistical analysis of data. We also are very grateful to G. Borgia and J. R. Madden for their valuable comments on this manuscript. This study was financially supported by the Grant-in-Aid for Scientific Research from the Japanese Society for Promotion of Science to KE (No. 14405007 and No. 17255003). This study was conducted under permits from Charles Darwin University Animal Ethics Committee, the Parks and Wildlife Commission of the Northern Territory, and the Australian Bird and Bat Banding Schemes.
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