Visual pigments, cone oil droplets and ocular media in four species of estrildid finch

A microspectrophotometric study was conducted on the retinal photoreceptors of four species of bird: cut-throat finches (Amadina fasciata), gouldian f inches (Erythrura gouldiae), white-headed munias (Lonchura maja) and plum-h eaded finches (Neochmia modesta). Spectral characteristics of the photorece ptors in all four species were very similar. Rods contained a medium-wavele ngth-sensitive visual pigment with a wavelength of maximum absorbance at 50 2-504 nm. Four spectrally distinct types of single cone contained a visual pigment with wavelength of maximum absorbance at either 370-373 nm (ultravi olet-sensitive), 440-447 nm (short-wavelength-sensitive); 500 nm (medium-wa velength-sensitive) or 562-565 nm (long-wavelength-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-wa velength-sensitive single cones had cut-off wavelengths at 415-423 nm, 510- 520 nm and 567-575 nm, respectively. Double cones contained the visual pigm ent with wavelength of maximum absorbance at 562-565 nm observed in long-wa velength-sensitive single cones. Only the principal member of the double co ne pair contained an oil droplet (P-type, cut-off wavelength at 414-489 nm depending on species and retinal location). Spectral transmittance of the i ntact ocular media of each species was measured along the optic axis. Wavel engths of 0.5 transmittance for all species were very similar (316-318 nm).