Bower Structure is a Good Predictor of Mating Success in the Great Bowerbird

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Male Great Bowerbirds Chlamydera nuchalis build a bower and pile decorations around it for courtship display. We tested the effect of the bower structure and amounts of decorations on the mating success of owner males in a population of C. n. nuchalis near Darwin, Northern Territory, Australia. We collected data on measurements of bowers and mating success of individual owner males for 16 and 14 bowers in 2005 and 2006, respectively. We used five variables (avenue length, avenue width, wall thickness, bower height and degree of asymmetry) corresponding to the bower structure, and two variables (coverage (%) of green decorations and that of all decorations) corresponding to amounts of decorations as explanatory variables. An analysis of the generalized linear mixed model and model selection revealed that avenue length and wall thickness affected mating success positively, and that of avenue width, negatively. Avenue length and wall thickness correspond to the size of the bower, which suggests that a larger bower provides females with better protection from a vigorous male's display. A long and narrow avenue may provide a refuge for females from the harassment by an owner male. No variables corresponding to decorations were important for the mating success.