Differential Response to Colors by the Lizard Uta palmeri (Reptilia: Iguanidae)

Many lizards have brightly colored body parts thought to be signals, but color perception in lizards has not been well studied. We present data documenting differential response to colors in an iguanid lizard. Free-living Uta palmeri differentially approached and bit at a red-colored object when simultaneously presented objects of four different colors (red, blue, yellow, black). This response to red was statistically significant for all three age-sex classes of lizards tested (adult males, adult females, juveniles). In addition, juveniles and adult females exhibited intermediate levels of responses (approaching and sniffing, and licking) to the yellow object but adult males did not. Seasonally important food items of this species are red (fish regurgitated by nesting seabirds) and yellow (yolk from broken seabird eggs), and response behavior (biting versus licking) was similar to that exhibited during feeding. Thus, as presented in our experimental paradigm, red and yellow elicited feeding responses. The spectral reflectance curves of the red and yellow stimuli were found to exhibit peaks at wavelengths of 630 nm (range 570–670), and at 600 nm (range 550–700), respectively. These values overlap with the spectral range of the gravid coloration of female U. palmeri (peak 615 nm, range 550–690) that is thought to be a signal to conspecifics. Furthermore, the reflectance curves are similar in shape and height (intensity). Thus, the similarities of the reflectance curves of the red paint and of the natural coloring suggest that palmeri can detect the female gravid coloration. Whether the response to red objects is due to discriminating differences in hue or in relative brightness remains to be examined.