Editing Hummingbird (section)

=== Vision ===
[[File:Rufous Hummingbird, male 01.jpg|thumb|left|Male rufous hummingbird (''Selasphorus rufus'') displaying a proportionally large eye in relation to its head]]

Although hummingbird eyes are small in diameter (5–6&nbsp;mm), they are accommodated in the [[skull]] by reduced skull [[ossification]], and occupy a larger proportion of the skull compared to other birds and animals.<ref name="ocampo">{{Cite journal |last1=Ocampo |first1=Diego |last2=Barrantes |first2=Gilbert |last3=Uy |first3=J. Albert C. |date=2018-09-27 |title=Morphological adaptations for relatively larger brains in hummingbird skulls |journal=Ecology and Evolution |volume=8 |issue=21 |pages=10482–10488 |doi=10.1002/ece3.4513 |issn=2045-7758 |pmc=6238128 |pmid=30464820|bibcode=2018EcoEv...810482O }}</ref>

Further, hummingbird eyes have large [[cornea]]s, which comprise about 50% of the total transverse eye diameter, combined with an extraordinary density of [[retinal ganglion cell]]s responsible for visual processing, containing some 45,000 [[neuron]]s per mm<sup>2</sup>.<ref name="lisney">{{Cite journal |author1=Lisney, T.J. |author2=Wylie, D.R. |author3=Kolominsky, J. |author4=Iwaniuk, A.N. |year=2015 |title=Eye morphology and retinal topography in hummingbirds (''Trochilidae Aves'') |url=https://www.karger.com/Article/FullText/441834 |journal=Brain, Behavior and Evolution |volume=86 |issue=3–4 |pages=176–190 |doi=10.1159/000441834 |pmid=26587582 |doi-access=free}}</ref> The enlarged cornea relative to total eye diameter serves to increase the amount of light perception by the eye when the [[pupil]] is dilated maximally, enabling [[nocturnal]] flight.<ref name="lisney" />

During evolution, hummingbirds adapted to the navigational needs of visual processing while in rapid flight or hovering by development of the exceptionally dense array of retinal neurons, allowing for increased [[spatial resolution]] in the [[geometric terms of location|lateral and frontal]] [[visual field]]s.<ref name=lisney/> [[Morphology (biology)|Morphological]] studies of the hummingbird brain showed that neuronal [[hypertrophy]] {{Ndash}} relatively the largest in any bird {{Ndash}} exists in a region called the ''[[pretectal area|pretectal]] nucleus lentiformis [[Midbrain|mesencephali]]'' (called the ''nucleus of the [[optic tract]]'' in mammals) responsible for refining dynamic visual processing while hovering and during rapid flight.<ref>{{Cite journal |author1=Iwaniuk, A.N. |author2=Wylie, D.R. |year=2007 |title=Neural specialization for hovering in hummingbirds: hypertrophy of the pretectal nucleus Lentiformis mesencephali |url=http://www.psych.ualberta.ca/~dwylie/Iwaniuk%20and%20Wylie%20JCN%202007.pdf |journal=Journal of Comparative Neurology |volume=500 |issue=2 |pages=211–221 |doi=10.1002/cne.21098 |pmid=17111358 |s2cid=15678218}}</ref><ref name="gaede">{{Cite journal |last1=Gaede |first1=A.H. |last2=Goller |first2=B. |last3=Lam |first3=J.P. |last4=Wylie |first4=D.R. |last5=Altshuler |first5=D.L. |year=2017 |title=Neurons responsive to global visual motion have unique tuning properties in hummingbirds |journal=Current Biology |volume=27 |issue=2 |pages=279–285 |doi=10.1016/j.cub.2016.11.041 |pmid=28065606 |doi-access=free |bibcode=2017CBio...27..279G |s2cid=28314419}}</ref>

The enlargement of the brain region responsible for visual processing indicates an enhanced ability for perception and processing of fast-moving visual stimuli encountered during rapid forward flight, insect foraging, competitive interactions, and high-speed courtship.<ref name=gaede/><ref name="sd2017">{{Cite web |date=5 January 2017 |title=Hummingbirds see motion in an unexpected way |url=https://www.sciencedaily.com/releases/2017/01/170105123115.htm |access-date=24 April 2017 |website=ScienceDaily}}</ref> A study of broad-tailed hummingbirds indicated that hummingbirds have a fourth [[Photoreceptor cell#Difference between rods and cones|color-sensitive visual cone]] (humans have three) that detects [[Ultraviolet|ultraviolet light]] and enables discrimination of [[Color#Spectral colors|non-spectral colors]], possibly having a role in flower identity, courtship displays, territorial defense, and predator evasion.<ref name="stoddard">{{Cite journal |author1=Stoddard, M.C. |author2=Eyster, H.N. |author3=Hogan, B.G. |author4=Morris, D.H. |author5=Soucy, E.R. |author6=Inouye, D.W. |date=2020-06-15 |title=Wild hummingbirds discriminate nonspectral colors |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=26  |display-authors=3 |pages=15112–122 |doi=10.1073/pnas.1919377117 |issn=0027-8424 |pmc=7334476 |pmid=32541035 |bibcode=2020PNAS..11715112S |doi-access=free}}</ref> The fourth color cone would extend the range of visible colors for hummingbirds to perceive ultraviolet light and color combinations of feathers and gorgets, colorful plants, and other objects in their environment, enabling detection of as many as five non-spectral colors, including purple, ultraviolet-red, ultraviolet-green, ultraviolet-yellow, and ultraviolet-purple.<ref name=stoddard/>

Hummingbirds are highly sensitive to stimuli in their visual fields, responding to even minimal motion in any direction by reorienting themselves in midflight.<ref name=gaede/><ref name=sd2017/><ref name="goller">{{Cite journal |author1=Goller, B. |author2=Altshuler, D.L. |year=2014 |title=Hummingbirds control hovering flight by stabilizing visual motion |journal=Proceedings of the National Academy of Sciences |volume=111 |issue=51 |pages=18375–380 |bibcode=2014PNAS..11118375G |doi=10.1073/pnas.1415975111 |pmc=4280641 |pmid=25489117 |doi-access=free}}</ref> Their visual sensitivity allows them to precisely hover in place while in complex and dynamic natural environments,<ref name=goller/> functions enabled by the [[lentiform nucleus]] which is tuned to fast-pattern velocities, enabling highly tuned control and collision avoidance during forward flight.<ref name=gaede/>