ORIGINAL PAPER N. S. Hart á J. C. Partridge á A. T. D. Bennett I. C. Cuthill Visual pigments, cone oil droplets and ocular media in four species of estrildid ®nch Accepted: 6 May 2000 / Published online: 10 June 2000 Ó Springer-Verlag 2000 Abstract A microspectrophotometric study was con- ducted on the retinal photoreceptors of four species of bird: cut-throat ®nches Amadina fasciata), gouldian ®nches Erythrura gouldiae), white-headed munias Lonchura maja) and plum-headed ®nches Neochmia modesta). Spectral characteristics of the photoreceptors in all four species were very similar. Rods contained a medium-wavelength-sensitive visual pigment with a wavelength of maximum absorbance at 502±504 nm. Four spectrally distinct types of single cone contained a visual pigment with wavelength of maximum absor- bance at either 370±373 nm ultraviolet-sensitive), 440±447 nm short-wavelength-sensitive); 500 nm me- dium-wavelength-sensitive) or 562±565 nm long-wave- length-sensitive). Oil droplets in the ultraviolet-sensitive single cones showed no detectable absorption between 330 nm and 800 nm. Oil droplets in the short-, medium-, and long-wavelength-sensitive single cones had cut-o wavelengths at 415±423 nm, 510±520 nm and 567± 575 nm, respectively. Double cones contained the visual pigment with wavelength of maximum absorbance at 562±565 nm observed in long-wavelength-sensitive sin- gle cones. Only the principal member of the double cone pair contained an oil droplet P-type, cut-o wavelength at 414±489 nm depending on species and retinal loca- tion). Spectral transmittance of the intact ocular media of each species was measured along the optic axis. Wavelengths of 0.5 transmittance for all species were very similar 316±318 nm). Key words Colour vision á Microspectrophotometry á Photoreceptor á Retina á Bird Abbreviations D dorsal á LWS long-wavelength- sensitive á MSP microspectrophotometer á MWS medium-wavelength-sensitive á PBS phosphate-buered saline á SWS short-wavelength-sensitive á UVS ultraviolet sensitive á V ventral á VS violet-sensitive á k max wavelength of maximum absorbance á k cut cut-o wavelength á k mid wavelength of half maximum measured absorptance á kT 0.5 wavelength of 0.5 transmittance Introduction The retinae of most diurnal birds studied to date con- tain a single class of medium-wavelength-sensitive MWS) rod, a single class of long-wavelength-sensitive LWS) double cone, and four classes of spectrally dis- tinct single cone which are maximally sensitive to long, medium, short, and either violet VS) or ultraviolet UVS) wavelengths Jane and Bowmaker 1988; Bow- maker et al. 1993, 1997; Maier and Bowmaker 1993; Hart et al. 1998; Das et al. 1999; Hart et al. 1999, 2000). The spectral sensitivity of a given photoreceptor cell is determined by the absorptance of the visual pigment in the outer segment and, in the case of avian or some reptilian cones, the transmittance of the oil droplet lo- cated in the ellipsoid region of the inner segment, through which some or all of the light incident upon the outer segment must have passed Baylor and Hodgkin 1973; Bowmaker 1977; Neumeyer and JaÈger 1985; Ka- wamuro et al. 1997). Each type of cone visual pigment is reliably associ- ated with a speci®c type of oil droplet. With the ex- ception of the transparent, or `T-type', oil droplets found in the VS/UVS single cones, which show no detectable absorption from at least 330 nm to 800 nm, they contain short-wavelength-absorbing pigments carotenoids) and are generally considered to act as long-pass cut-o ®lters Liebman and Granda 1975; Goldsmith et al. 1984; Lipetz 1984b). The dierence in spectral transmittance between droplet types depends on the type and concentration of the carotenoids they contain. J Comp Physiol A 2000) 186: 681±694 Digital Object Identi®er DOI) 10.1007/s003590000121 N. S. Hart á J. C. Partridge &) á A. T. D. Bennett á I. C. Cuthill School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK e-mail: j.c.partridge@bristol.ac.uk Tel.: +44-117-928-7591; Fax: +44-117-925-7373