A grey squirrel spectral sensitivity by heterochromatic flicker and its implications

Abstract

A behavioural spectral sensitivity curve for the grey squirrel ( Sciurus carolinensis leucotis). at a light level about 3.5 log units above its scotopic threshold, is found by heterochromatic flicker photometry. The overall sensitivity maximum is near 525 nm, and there is a dip in the curve near 491 nm. significant at the ± 95% confidence level, as found in other squirrels. The possible contribution of a colour-opponent system is considered. In view of Loew's MSP identification of P500 in the r-type, and P543 in the c-type receptors, the relationship of the squirrel's visual performance to these pigments is discussed. In the absence of any other receptor type, the possibility is considered that the structurally ambiguous r-type might take part in antagonistic interaction at photopic levels, as well as mediating scotopic vision.