Received: SeptemAccepted: FebruPublished: March 29, 2017Ĭopyright: © 2017 Tyrrell, Fernández-Juricic. PLoS ONE 12(3):Įditor: Daniel Osorio, University of Sussex, UNITED KINGDOM Overall, we argue that there is more to avian binocularity than meets the eye.Ĭitation: Tyrrell LP, Fernández-Juricic E (2017) Avian binocular vision: It’s not just about what birds can see, it’s also about what they can’t. We discuss different strategies-wide binocular fields, large eye movements, and long beaks-that minimize the potential negative effects of the anterior blind area. But in non-visually guided foragers, there is no consistent relationship between the beak and anterior blind area. For example, fish- and insect-eating specialists can see more of their own beak than birds eating immobile food can. In visually guided foragers, the ability to see the beak-and how much of the beak can be seen-varies predictably with foraging habits.
This result suggests that the anterior blind area and beak visibility do play a role in shaping binocular fields, and that binocular field width is not solely determined by the need for stereoscopic vision. We found that birds with proportionally longer beaks have longer anterior blind areas and thus narrower binocular fields. We used published data on visual field configuration in 40 species of birds and measured beak and skull parameters from museum specimens. We tested for the first time some specific predictions about the functional role of the anterior blind area in birds controlling for phylogenetic effects. Additionally, the anterior blind area is of functional significance for birds because the beak falls within this blind area. Therefore, species with wider binocular fields also have shorter anterior blind areas and objects along the mid-sagittal plane can be imaged at closer distances. This anterior blind area is important when discussing the evolution of binocular vision because its relative length is inversely correlated with the width of the binocular field. However, the blind area in front of the head that is proximal to the binocular visual field is often neglected.
Binocular vision in vertebrates has been implicated in several functions, including depth perception, contrast discrimination, etc. With the exception of primates, most vertebrates have laterally placed eyes.
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