No evidence for a ‘warning effect’ of blue light in roe deer

Physiological investigations of cervid eyes have revealed two different types of cones indicating high visual sensitivity in the ‘blue’ and ‘green’ spectral range (400–450 nm and 510–540 nm). Although detailed knowledge about light perception in large mammals is still missing, light reflecting devices such as wildlife warning reflectors are frequently used in animalvehicle collision mitigation. Light of wavelengths in the range of 440–490 nm (‘blue’ light) has recently been advocated to evoke a warning effect in cervids due to its rare occurrence in the natural environment. We conducted a behavioural study with captive roe deer Capreolus capreolus to investigate whether roe deer exhibit a specific behavioural response to ‘blue’ light (wavelengths 440–490 nm). Compartmented feeders were pseudo‐randomly illuminated with either ‘blue’ (colour: blue, 440–490 nm) or ‘warm‐white’ light (colour: yellow‐orange, 575–675 nm), or left unilluminated to assess changes in feeding time and feeder‐compartment choice in dependence of illumination. Although feeding times were found to be generally shorter under illumination there was no difference between illumination types. Moreover, roe deer favoured the illuminated feeder compartment over non‐illuminated ones. Our results highlight that roe deer differentiate between light and no light conditions while ‘blue’ light (440–490 nm) did not exert a ‘warning effect’ in roe deer.