Species‐specific differences in relative eye size are related to patterns of edge avoidance in an Amazonian rainforest bird community

• Published in: Ecology and evolution Vol. 4; no. 19; pp. 3736 - 3745
• Main Authors: Martínez‐Ortega, Cristina, Santos, Eduardo S.A., Gil, Diego
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01-10-2014; BlackWell Publishing Ltd
• Subjects: Acuity; Animal behavior; Avian vision; Avoidance; Birds; Body size; Communication; Communities; ecology; Eye; Eye (anatomy); Foraging habitats; Forests; habitat use; Habitats; Light; light environment; Microenvironments; Microhabitats; Nocturnal; Occupancy; Original Research; perception; Predation; Prey; Rainforests; Species; Strata; Tropical forests; Visual acuity; Brazil; Amazon Basin; habitat use; ecology; Avian vision; light environment; perception
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.1194

Eye size shows a large degree of variation among species, even after correcting for body size. In birds, relatively larger eyes have been linked to predation risk, capture of mobile prey, and nocturnal habits. Relatively larger eyes enhance visual acuity and also allow birds to forage and communicate in low‐light situations. Complex habitats such as tropical rain forests provide a mosaic of diverse lighting conditions, including differences among forest strata and at different distances from the forest edge. We examined in an Amazonian forest bird community whether microhabitat occupancy (defined by edge avoidance and forest stratum) was a predictor of relative eye size. We found that relative eye size increased with edge avoidance, but did not differ according to forest stratum. Nevertheless, the relationship between edge avoidance and relative eye size showed a nonsignificant positive trend for species that inhabit lower forest strata. Our analysis shows that birds that avoid forest edges have larger eyes than those living in lighter parts. We expect that this adaptation may allow birds to increase their active daily period in dim areas of the forest. The pattern that we found raises the question of what factors may limit the evolution of large eyes.
In the Amazonian rain forest, strong differences in light conditions exist between the edge and the interior of the forest. Bird species in this areas differ in the extent to which they avoid borders and favour the interior of the forest. Here we show that birds that avoid forest edges have larger eyes for their size, and this presumably help them dwell in dim light conditions.