Bower paint removal leads to reduced female visits, suggesting bower paint functions as a chemical signal

The multifaceted courtship display of male satin bowerbirds, Ptilonorhynchus violaceus, involves several elements that have been studied in detail. However, one of their most unique display elements, bower painting, has received relatively little attention despite males' large investment of time in this behaviour. Male bowerbirds chew plant material and apply the resulting mixture of masticated vegetation and male saliva or 'bower paint' to a chest-high band inside their bower walls. Searching females taste this paint, suggesting that paint may be a chemosensory signal. We used both behavioural observations and experimental approaches to examine predictions made by two hypotheses for the function of bower paint. We measured natural variation in paint quantity to investigate whether quantity of paint at bowers is related to other male display traits, male mating success and male physical condition. We also investigated whether males and females are affected by experimental removal of bower paint. Additionally, we assessed male response to paint transplants from other individuals. We found a significant correlation between the amount of paint and a composite estimate of several other measures known to indicate bower and decoration display quality. Also, males whose bowers underwent experimental removal of paint had fewer females return for second courtships and copulations than did control males. This result provides the first experimental evidence that females respond to bower paint. These findings establish that bower paint is a trait that affects mate-searching decisions by females and demonstrates that the quantity of bower paint is important in attracting females.