Stealing behavior and the maintenance of a visual display in the satin bowerbird

Honest signals that indicate male quality have been observed in many species and are thought to have evolved to allow males to assess rivals accurately and respond to "cheaters." Females could potentially also use the same honest signals as reliable indicators of male quality. In bowerbirds, the numbers of specific bower decorations may serve as an honest signal of male quality: this study investigates whether decoration stealing among male satin bowerbirds at the Bunya Mountains, Australia, may also involve honest signals. In this study, we aimed to determine 1) predictors for the degree to which individual male satin bowerbirds steal, and are stolen from, and 2) predictors for why some male pairs interact by stealing, whereas other pairs do not. We also assessed how experimentally standardizing the number of decorations on bowers would affect the 1) frequency of stealing, 2) specific interactions among males, and 3) distribution of decorations across bowers. Bower decorations were labeled and tracked through one breeding season. Males that were successful stealers, stole from other successful stealers, had many feathers and bottle tops on their bowers and painted their bower walls often. Male pairs were more likely to interact by stealing if their bowers were in close proximity. Most of the stealing observed was of a reciprocal nature. After we standardized the numbers and types of decorations on a small group of males' bowers, the mean number of daily stealing gains and the total number of males interacting by stealing did not change. In addition, no significant novel stealing interactions were initiated after the manipulation. The average number of all bower decorations and the average number of rosella feathers on a given male's bower prior to the manipulation were proportional to the average numbers for the period after the manipulation. Furthermore, males that originally had better collections of decorations tended to suffer fewer losses due to stealing after the manipulation. Our results suggest that the total number of decorations, the total number of rosella feathers on a male's bower, and possibly stealing behavior, may form part of the basis of an honest signal indicating male quality and therefore might be correlated with mating success. Copyright 2007, Oxford University Press.