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What big eyes you have!

Eye size shows a large degree of variation among species, even after correctingfor body size. In birds, relatively larger eyes have been linked to predation risk,capture of mobile prey, and nocturnal habits. Relatively larger eyes enhancevisual acuity and also allow birds to forage and communicate in low-light situations.Complex habitats such as tropical rain forests provide a mosaic of diverselighting conditions, including differences among forest strata and at differentdistances from the forest edge. We examined in an Amazonian forest bird communitywhether microhabitat occupancy (defined by edge avoidance and foreststratum) was a predictor of relative eye size. We found that relative eye sizeincreased with edge avoidance, but did not differ according to forest stratum.Nevertheless, the relationship between edge avoidance and relative eye sizeshowed a nonsignificant positive trend for species that inhabit lower foreststrata. Our analysis shows that birds that avoid forest edges have larger eyesthan those living in lighter parts. We expect that this adaptation may allowbirds to increase their active daily period in dim areas of the forest. The patternthat we found raises the question of what factors may limit the evolution oflarge eyes.


  • Amazonian forest edge