Visual pigments, oil droplets, ocular media and cone photoreceptor distribution in two species of passerine bird: the blue tit (Parus caeruleus L.) and the blackbird (Turdus merula L.)

J Comp Physiol A. 2000 Apr;186(4):375-87. doi: 10.1007/s003590050437.


The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the visual pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (lambda(max)) of long-wavelength-sensitive single and double cone visual pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitive-single cones of both species cut off wavelengths below 570-573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise lambda(max) of the long-wavelength-sensitive visual pigment is optimised for the visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their visual ecology.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Absorption
  • Analysis of Variance
  • Animals
  • Anterior Eye Segment / chemistry
  • Anterior Eye Segment / physiology*
  • Aqueous Humor / chemistry
  • Aqueous Humor / physiology
  • Color Perception / physiology*
  • Cornea / chemistry
  • Cornea / physiology
  • Lens, Crystalline / chemistry
  • Lens, Crystalline / physiology
  • Oils / analysis
  • Retinal Cone Photoreceptor Cells / chemistry
  • Retinal Cone Photoreceptor Cells / cytology
  • Retinal Cone Photoreceptor Cells / physiology*
  • Retinal Pigments / analysis
  • Retinal Pigments / physiology*
  • Retinal Rod Photoreceptor Cells / physiology
  • Songbirds / physiology*
  • Species Specificity
  • Spectrophotometry, Ultraviolet
  • Vitreous Body / chemistry
  • Vitreous Body / physiology


  • Oils
  • Retinal Pigments