The roles of receptor noise and cone oil droplets in the photopic spectral sensitivity of the budgerigar, Melopsittacus undulatus
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Individual budgerigars (Melopsittacus undulatus) were taught to detect narrow bands of wavelengths under ambient illumination of known spectral composition. Because the cone pigments of this species of bird have been identified and data on carotenoid absorbance present in the cone oil droplets are available, predictions of the Vorobyev-Osorio equations can be calculated with reasonable confidence. Based on more than 27,600 individual choices made by several birds at 10 wavelengths, the photopic sensitivity (i.e., color thresholds) of these birds is found to be consistent with the hypothesis that threshold discrimination of colored targets is limited by receptor noise and that high sensitivity to near-ultraviolet wavelengths is in harmony with the relatively small number of ultraviolet cones present in the retina. The pronounced fine structure of the sensitivity spectrum is caused by the absorption of cone oil droplets. Under natural sunlight, containing more energy in the near-ultraviolet than is present in artificial indoor lighting, the birds' peak of sensitivity in the ultraviolet should be much less prominent than it is in laboratory experiments.
KeywordsBird vision Budgerigars Color discrimination Cone oil droplets Receptor noise
This work was supported by NSF Grant No. 9816069. We are grateful to Daniel Osorio for commenting on a draft of the manuscript. These experiments comply with current laws in the United States, and the protocols for care and feeding of the birds were approved by the Institutional Animal Care and Use Committee of Yale University.
- Burkhardt D, Maier E (1989) The spectral sensitivity of a passerine bird is highest in the UV. Naturwissenschaften 76:82–83Google Scholar
- Kavanau JL (1987) Lovebirds, cockatiels, budgerigars: behavior and evolution. Science Software Systems, Los Angeles, CAGoogle Scholar
- Kelber A, Vorobyev M, Osorio D (2003) Animal colour vision— behavioural tests and physiological concepts . Biological Reviews (of the Cambridge Philosophical Society) (in press)Google Scholar
- Maier EJ (1992) Spectral sensitivities including the UV of the passeriform bird Leiothrix lutea. J Comp Physiol A 170:709–714Google Scholar
- Maier EJ, Bowmaker JK (1993) Colour vision in the passeriform bird, Leiothrix lutea: Correlation of visual pigments, absorbance, and oil droplet transmission with spectral sensitivity. J Comp Physiol A 172:295–301Google Scholar
- Morton ES (1982) Grading, discreteness, redundancy, and motivational-structural rules. In: Kroodsma D, Miller EH (eds) Acoustic communication in birds. Academic Press, New York, 183–212Google Scholar
- Palacios AG, Goldsmith TH, Bernard GD (1996) Sensitivity of cones from a cyprinid fish (Danio aequipinnatus) to ultraviolet and visible light. Vis Neurosci 13:411–421Google Scholar
- Pepperburg IM (1999) The Alex studies: cognitive and communicative abilities of grey parrots. Harvard University Press, Cambridge, MAGoogle Scholar
- Vorobyev M, Osorio D (1998) Receptor noise as a determinant of colour thresholds. Proc R Soc Lond Ser B 265:351–358Google Scholar
- Wilkie SE, Vissers PMAM, Das D, Degrip WJ, Bowmaker JK, Hunt DM (1998) The molecular basis for UV vision in birds—spectral characteristics, cDNA sequence and retinal localization of the UV-sensitive visual pigment of the budgerigar (Melopsittacus undulatus). Biochem J 330:541–547PubMedGoogle Scholar