Bower characteristics and spatial arrangement of decorations among Vogelkop Bowerbirds of the Arfak Mountains, West Papua

Vogelkop Bowerbirds (Amblyornis inornatus) of the hut-building populations in West Papua build the most elaborately decorated structure in the animal kingdom excluding humans, consisting of a roofed hut and a forecourt with piles of flowers, fruits and other items. A previous study of the species in the Arfak Mountains concluded that both hut size and the areal coverage of blue decorations on courts were important in determining mating success. We measured the characteristics of 13 bowers in a dense population of the species, located only 44 km from the previous study site, and found no correlation between hut size and coverage of colourful decorations. Multivariate analyses indicated that the number of flowers and orange or red items were the most important variables distinguishing bowers from each other. The location of decorations was not random. Fleshy fruits and orange flowers were mostly placed on the left side of the court or inside the hut, while blackish dry fruits/fungi/wood were typically on the right side or off-court. The majority of bowers faced north (±45°), allowing decorations to be illuminated most of the day, while limiting the light that enters the hut during the morning. Video taken at three bowers suggested that the owner of the bower with the most decorations and highest illumination was the most successful in mating. We propose different functions for the hut and court: court decorations serve to attract females to bowers, while the hut functions primarily to hide the displaying male prior to and during mating.