Colour vision in Finlayson’s squirrel (Callosciurus finlaysonii): is conspicuous pelage colour useful for species recognition?

Finlayson’s squirrel, Callosciurus finlaysonii, is distributed in lowland forests throughout South-East Asia. Its pelage colour is conspicuous and polymorphic (red, black, white and a mixture of these colours), which is characteristic of the species, with 16 subspecies described based on pelage colour patterns. Two closely related species, the brown C. erythraeus and the orange C. caniceps, are also distributed throughout the region. To examine whether the conspicuous pelage colour is a visual clue for species/subspecies discrimination, we experimentally assessed the colour vision of C. finlaysonii. Optically measured pelage colours of the dorsal body differed greatly among seven subspecies of C. finlaysonii and also differed among the three species of the region. Colour vision tests revealed that C. finlaysonii can discriminate the colour of conspecific white, black, and red pelages from the orange pelages of C. caniceps. They can also discriminate the brown pelages of C. erythraeus and conspecific white and black pelages, but they cannot discriminate between the brown and red pelages because they have dichromatic colour vision. White, black and orange pelage colours could be useful clues for species/subspecies recognition in Callosciurus.