Flower choice and bower decoration in the satin bowerbird Ptilonorhynchus violaceus: a test of hypotheses for the evolution of male display

Abstract

Flowers are a common decoration used on the bowers of male satin bowerbirds. The characteristics of flowers that promote their use as decorations by males are evaluated. Out of a total of 70 species recorded along transects, inflorescences from 29 species were found on bowers. Seven flower species accounted for 93% of the inflorescences used on bowers. Blue and purple species occurred on bowers at a greater frequency than they occurred in the habitat. White and yellow species appeared on bowers proportionately less often, and orange, pink and red not at all. Male satin bowerbirds used a wider range of colours of flowers than has been previously reported, and preferred blue and purple over yellow and white flowers. Flower choice experiments showed that males may discriminate between flowers only on the basis of colour, and that males favour flowers that appear infrequently on bowers. The results suggest several conclusions about how flowers are used on bowers. (1) Male flower preferences and male ability to collect inflorescences affect how flowers are used on bowers. The common use of flowers shown to be less preferred in choice tests implies that there are constraints on the gathering of more preferred flowers and this causes males to produce suboptimal displays. (2) Male preference for novel flowers suggests that flower choice by males is due to a set of general selection criteria and does not result from preferences for specific flower species. (3) The strong male preference for, and the high rate of use of, rare blue flowers supports the hypothesis that the rarity of colours may influence the evolution of male flower references. This strong preference for scarce flowers offers some support for models that suggest that male displays are not arbitrary, but may serve as indicators of male quality as sires.