Sm Pearn

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

As in many parrots, the plumage of the budgerigar Melopsittacus undulatus reflects near–ultraviolet (UVA) wavelengths (300–400 nm) and exhibits UVA–induced fluorescence. However, there have, to our knowledge, been no tests of whether the yellow fluorescence observed under intense UVA illumination has any role in signalling. Four experiments were carried out on wild–type budgerigars, where the presence and absence of UV reflectance and fluorescence were manipulated using filters. Few studies have attempted to separate the contribution of UV reflectance to plumage hue as opposed to brightness or distinguish between a role in sexual as opposed to social preferences. However, our first experiments show that not only do females consistently prefer UV–reflecting males, but also that the observed preferences are due to removal of UV affecting the perceived hue rather than brightness. Furthermore, we found no effect of the light environment on male response to females, suggesting that the female preferences relate to plumage colour per se. Whilst UV reflectance appears important in heterosexual choice by females, it has no detectable influence on same–sex association preferences. The results from the second series of experiments suggest that enhancement of the budgerigars yellow coloration through fluorescence has no effect on male attractiveness. However, the fluorescent plumage may play a role in signalling by virtue of the fact that it absorbs UVA and so increases contrast with nearby UV–reflecting plumage. Our study provides convincing evidence that UV reflectances can play a role in mate choice in non–passerines, but no evidence that the yellow fluorescence observed under UVA illumination is itself important as a signal.

The role of ultraviolet-A reflectance and ultraviolet-A induced fluorescence in the appearance of budgerigar plumage: insights from spectrofluorometry and reflectance spectrophotometry.

Fluorescence has so far been found in 52 parrot species when illuminated with ultraviolet–A (UVA) ‘black’ lamps, and two attempts have been made to determine whether such fluorescence plays any role in sexual signalling. However, the contribution of the reflectance versus fluorescence to the total radiance from feathers, even in the most studied species to date (budgerigars), is unclear. Nor has the plumage of this study species been systematically assessed to determine the distribution of fluorescent patches. We therefore used spectrofluorometry to determine which areas of budgerigars fluoresce and the excitation and emission spectra involved; this is the first time that such a technique has been applied to avian plumage. We found that both the yellow crown and (normally hidden) white downy chest feathers exhibit strong UVA–induced fluorescence, with peak emissions at 527 nm and 436 nm, respectively. Conversely, the bright–green chest and dark–blue tail feathers do not fluoresce. When comparing reflectance spectra (400–700 nm) from the yellow crown using illuminants with a proportion of UVA comparable to daylight, and illuminants with all UVA removed, no measurable difference resulting from fluorescence was found. This suggests that under normal daylight the contribution of fluorescence to radiance is probably trivial. Furthermore, these spectra revealed that males had fluorescent crowns with substantially higher reflectance than those of females, in both the UV waveband and at longer wavelengths. Reflectance spectrophotometry was also performed on a number of live wild–type male budgerigars to investigate the chromatic contrast between the different plumage areas. This showed that many plumage regions are highly UV–reflective. Overall our results suggest that rapid surveys using UVA black lamps may overestimate the contribution of fluorescence to plumage coloration, and that any signalling role of fluorescence emissions, at least from the yellow crown of budgerigars, may not be as important as previously thought.

Correction for Pearn et al., Ultraviolet vision, fluorescence and mate choice in a parrot, the budgerigar Melopsittacus undulatus

Correction for ‘Ultraviolet vision, fluorescence and mate choice in a parrot, the budgerigar Melopsittacus undulatus’ by S. M. Pearn, A. T. D. Bennett and I. C. Cuthill (Proc. R. Soc. Lond. B 268, 2273–2279. (doi: 10.1098/rspb.2001.1813)). On page 2275, §2d(i), the word ‘negative’ was incorrectly printed as ‘positive’.