SMALL PASSERINES CAN DISCRIMINATE ULTRAVIOLET SURFACE COLORS

Hollow-dwelling passerine birds were tested for UV surface colour disc rimination by using the instinct to bring food to nestlings that makes a bird search for the nest under changing conditions. The experiments were carried out on breeding pairs of pied flycatcher (Muscicapa hypo leuca), great tit (Parus major) and tree sparrow (Passer montanus) in the wild by the method of alternative choice of entrance into a double nesting-box with the nestlings in one or the other section. The entra nces were marked with sheets of painted papers that had different refl ectances in UV. For a human observer, all marks looked achromatic. Bir ds were trained to discriminate the mark coloured with UV-absorbing pa int from a neutral one (with equal reflectance throughout the spectrum ). Birds easily learned to search for the UV-absorbing mark, and trans ferred the acquired habit when tested with new marks that differed onl y slightly from the initial ones in lightness to eliminate brightness cues.