Spectral sensitivity and colour vision in the ground-dwelling sciurids: results from golden mantled ground squirrels and comparisons for five species.

Behavioural measurements of several indices of visual sensitivity and colour vision for the golden-mantled ground squirrel (Spermophilus lateralis) are reported. The spectral sensitivity functions for this animal show a change from having a single peak at about 520 nm to having a strongly bipartite appearance with peaks at about 540 and 460 nm as the level of light adaptation is increased from low to higher levels. Discrimination tests reveal that these squirrels have dichromatic colour vision with spectral neutral points centered at 507.5 nm. Comparisons are made of the visual capacities of five species of ground-dwelling sciurids, all of which have been tested in the same situations. These comparisons indicate that: (1) the retinas of all of these species contain a small number of functional rods in addition to a much more obvious cone population; (2) the spectral sensitivity functions of these species do not show systematic variations; (3) the cone pigments found in the retinas of these animals have sensitivity peaks at about 440 and 525 nm; (4) all of these species have dichromatic colour vision; (5) there is no evidence for systematic differences in visual sensitivity or colour vision among these five species.