Skip to main content
Dryad

Ecological and Morphological Correlates of Acuity in Birds

Data files

Jan 12, 2024 version files 9.47 MB

Abstract

Birds use their visual systems for a variety of important tasks, such as foraging and predator detection, that require them to resolve an image. However, visual acuity (the ability to perceive spatial detail) varies by two orders of magnitude across birds. Prior studies indicate that eye size and aspects of a species’ ecology may drive variation in acuity, but these studies have been restricted to small numbers of species. We used a literature review to gather data on acuity measured either behaviorally or anatomically for 94 species from 38 families. We then examined how acuity varies in relation to (1) eye size, (2) habitat spatial complexity, (3) habitat light level, (4) diet composition, (5) prey mobility, and (6) foraging mode. A phylogenetically-controlled model including all of the above factors as predictors indicated that eye size, habitat spatial complexity, light level, and diet composition are significant predictors of acuity. Examining each ecological variable in turn revealed that acuity is lower in species that inhabit spatially complex, vegetative habitats, and higher in species whose diet comprises vertebrates or scavenged food. Together, our results suggest that the need to detect important objects from far away—such as predators for species that live in open habitats, and food items for species that forage on vertebrate and scavenged prey—has likely been a key driver of higher acuity in some species, helping to elucidate how visual capabilities may be adapted to an animal’s visual needs.