Color vision of the endemic Nēnē, or Hawaiian Goose (Branta sandvicensis): a case study

Abstract Color vision is a key aspect of bird vision; however, only 2 out of the 172 species in the Anatidae family have been fully studied. We characterize the color visual system properties of a third species, the Hawaiian island endemic goose, the Nēnē ( Branta sandvicensis ). We measured eye size, ocular media transmittance, retinal opsin sequences, photoreceptor sensitivity, and relative photoreceptor densities. We found that the Nēnē has a violet-sensitive visual system containing all five opsin classes typical of multiple bird species, including those in the Anatidae family. Compared to other Anatidae species, the Nēnē has relatively higher sensitivity to wavelengths of light particularly in the ‘green’ and ‘yellow’ portions of the visible light spectrum, relatively lower ultraviolet transmittance through the ocular media, and relatively higher relative densities of medium-wavelength sensitive single cones. Several physiological parameters of the single Nēnē examined in this study differed from those of their closest living relative and sister taxon, the Canada Goose ( Branta canadensis ), suggesting that color vision can diverge between two closely related species. We also provide the parameters necessary for perceptual modeling of the Nēnē visual system for use in future avian deterrent development.