Data from: Individual variation in cone photoreceptor density in house sparrows: implications for between-individual differences in visual resolution and chromatic contrast

Between-individual variation has been documented in a wide variety of
taxa, especially for behavioral characteristics; however, intra-population
variation in sensory systems has not received similar attention in wild
animals. We measured a key trait of the visual system, the density of
retinal cone photoreceptors, in a wild population of house sparrows
(Passer domesticus). We tested whether individuals differed from each
other in cone densities given within-individual variation across the
retina and across eyes. We further tested whether the existing variation
could lead to individual differences in two aspects of perception: visual
resolution and chromatic contrast. We found consistent between-individual
variation in the densities of all five types of avian cones, involved in
chromatic and achromatic vision. Using perceptual modeling, we found that
this degree of variation translated into significant between-individual
differences in visual resolution and the chromatic contrast of a plumage
signal that has been associated with mate choice and agonistic
interactions. However, there was no evidence for a relationship between
individual visual resolution and chromatic contrast. The implication is
that some birds may have the sensory potential to perform “better” in
certain visual tasks, but not necessarily in both resolution and contrast
simultaneously. Overall, our findings (a) highlight the need to consider
multiple individuals when characterizing sensory traits of a species, and
(b) provide some mechanistic basis for between-individual variation in
different behaviors (i.e., animal personalities) and for testing the
predictions of several widely accepted hypotheses (e.g., honest
signaling).