The visual acuity and refractive state of the American kestrel (Falco sparverius).

The pattern electroretinogram (PERG) was used to measure the visual acuity and refractive state of nine American kestrels (Falco sparverius). Visual acuity was determined from psychometric functions of PERG amplitude vs. spatial frequency. Refractive state was measured by finding the trial lens that resulted in the highest acuity. All nine kestrels were found to be emmetropic. Their median visual acuity was 29 c/deg. The PERG, however, underestimates behaviorally determined visual acuity by approximately 37%. When adjusted for this underestimation, the median kestrel acuity was 46 c/deg. The visual acuity of American kestrels is compared to reports in the literature of 17 other species of birds.