Eye Size, Foraging Methods and the Timing of Foraging in Shorebirds

1. Birds with large eyes can achieve a greater pupil diameter and/or focal length, and hence, all other things being equal, greater visual sensitivity and resolution than birds with small eyes. Thus eye size is predicted to reflect adaptations to ecology. 2. We tested three predictions about the relationships between eye size, foraging method (from wholly visual to tactile techniques) and the daily pattern of foraging activity (diurnal/nocturnal) in shorebirds, using phylogenetic comparative methods. 3. We found that shorebirds that forage at night were more likely to have large eyes, but species using vision to detect their prey did not have larger eyes than species that detect their prey by touch. We also found no evidence that nocturnal foragers are more likely than diurnal foragers to use tactile rather than visual cues to detect their prey. 4. These results indicate that evolutionary changes toward nocturnal habits are associated with increases in eye size, and thus with increases in aspects of visual capacity, but that foraging mode may not be the prime selective force in this taxon.