Ultraviolet vision, fluorescence and mate choice in a parrot, the budgerigar Melopsittacus undulatus

As in many parrots, the plumage of the budgerigar Melopsittacus undulatus r eflects near-ultraviolet (UVA) wavelengths (300-400 nm) and exhibits UVA-in duced fluorescence. However, there have, to our knowledge, been no tests of whether the yellow fluorescence observed under intense UVA illumination ha s any role in signalling. Four experiments were carried out on wild-type bu dgerigars, where the presence and absence of UV reflectance and fluorescenc e were manipulated using filters. Few studies have attempted to separate th e contribution of UV reflectance to plumage hue as opposed to brightness or distinguish between a role in sexual as opposed to social preferences. How ever, our first experiments show that not only do females consistently pref er UV-reflecting males, but also that the observed preferences are due to r emoval of UV affecting the perceived hue rather than brightness. Furthermor e, we found no effect Of the light environment on male response to females, suggesting that the female preferences relate to plumage colour per se. Wh ilst UV reflectance appears important in heterosexual choice by, females, i t has no detectable influence on same-sex association preferences. The resu lts from the second series of experiments suggest that enhancement of the b udgerigar's yellow coloration through fluorescence has no effect on male at tractiveness. However, the fluorescent plumage may play a role in signallin g by virtue of the fact that it absorbs UVA and so increases contrast with nearby UV-reflecting plumage. Our study provides convincing evidence that U V reflectances can play a role in mate choice in non-passerines, but no evi dence that the yellow fluorescence observed under UVA illumination is itsel f important as a signal.