Wavelength discrimination in the ‘visible’ and ultraviolet spectrum by pigeons

Using operant conditioning methods, the pigeon's wavelength discrimination abilities were assessed in two experiments to generate discrimination functions. Both these functions showed three minima at 460, 530 and 595 nm. In the second wavelength discrimination experiment, extending measurements into the UV spectral region, pigeons also maintained good discrimination between wavelengths within the UV range tested. A fourth minimum was indicated at the lower end of the spectral range tested (365–385 nm). The results point to the complexity of the pigeon's chromatic system, which must be at least tetrachromatic, probably pentachromatic.