Sensory capacities and the nocturnal habit of owls (Strigiformes)

Abstract

Behavioural studies show that in the eye of the Tawny Owl Strix aluco both absolute visual sensitivity and maximum spatial resolution at low light levels are close to the theoretical limit dictated principally by the quantal nature of light and the physiological limitations on the structure of vertebrate eyes. However, when the owl's visual sensitivity in relation to naturally occurring ligh levels is analysed, it is concluded that at night there will often be occasions when vision can only be used to control the owl's behaviour with respect to large objects.Owls are capable of detecting and catching prey by hearing alone. However, absolute auditory sensitivity is not superior to that of mammals (including Man), but does appear to have reached the absolute limit on sensitivity in the aerial environment, which is dictated by the minimum ambient sound level.An explanation of the owl's ability to be active at night based only upon high sensory sensitivity is thus untenable. Many features of the natural behaviour of the Tawny Owl (e.g., the high degree of territoriality, prey catching technique, dietary spectrum) may be interpreted as reflections of an additional requirement for the nocturnal habit beyond high sensory sensitivity: detailed knowledge of local topography.