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Published online by Cambridge University Press: 27 February 2018
Colour is an important feature that increases the visibility of objects and may aid recognition of con-specifics. The adaptive significance of the ability to utilize colour cues has been demonstrated in a number of species, in particular in relation to food selection. The evolution of trichromatic colour vision in primates has been associated with the advantages that it provided in the selection of yellow and orange fruits (Mollon, 1989) or tender young red foliage (Dominy and Lucas, 2001) from a background of green. The horse is a generalist herbivore that must both select nutritious plants and avoid toxic ones. Familiarity is an important factor in this selection process (Augner et al., 1998), although it is not clear exactly what features are used to recognise previously ingested and “safe” herbage.
The horse has been shown to possess dichromatic colour vision. There are two types of cone photopigment in the equine retina, with spectral peaks at 429 and 545 nanometres (Macuda, 2000).