Increment-threshold spectral sensitivity in the tawny owl ( Strix aluco)

Abstract

Colour vision has previously been shown to be present in the tawny owl ( Strix aluco)—a totally nocturnal bird. Photopic increment-threshold spectral sensitivity functions were behaviourally determined in three tawny owls, using a two-choice simultaneous discrimination procedure. The functions obtained from the three birds showed very close agreement. All had maximum sensitivity at about 580 nm and in two of the birds a submaximum at about 525 nm was evident. A comparison is made between this function and that from two humans tested in the same apparatus. The possible effects of selective absorption by pre-retinal media on the owl's function are considered. The owl's function is compared with similar data available for other species of bird.