Editing Turtle (section)

=== Senses ===
[[File:Red Eared Slider's Eye.jpg|thumb|The [[red-eared slider]] has an exceptional seven types of color-detecting cells in its eyes.<ref name="Fritsches et al 2013"/>|alt=head of a red-eared slider turtle|left]]

Turtles make use of [[Visual perception|vision]] to find food and mates, avoid predators, and orient themselves. The [[retina]]'s light-sensitive cells include both [[Rod cell|rods]] for vision in low light, and [[Cone cell|cones]] with three different [[photopigment]]s for bright light, where they have full-color vision. There is possibly a fourth type of cone that detects [[ultraviolet]], as hatchling sea turtles respond experimentally to ultraviolet light, but it is unknown if they can distinguish this from longer wavelengths. A freshwater turtle, the [[red-eared slider]], has an exceptional seven types of cone cell.<ref name="Fritsches et al 2013"/><ref name="Granda Dvorak 1977 pp. 451–495">{{cite book |last1=Granda |first1=Alan M. |last2=Dvorak |first2=Charles A. |title=The Visual System in Vertebrates |chapter=Vision in Turtles |series=Handbook of Sensory Physiology |publisher=Springer Berlin Heidelberg |publication-place=Berlin, Heidelberg |year=1977 |volume=7 / 5 |issn=0072-9906 |doi=10.1007/978-3-642-66468-7_8 |pages=451–495|isbn=978-3-642-66470-0 }}</ref><ref name="Jacobs 1981">{{cite book |last=Jacobs |first=Gerald |chapter=Reptiles: The Turtle |title=Comparative Color Vision |publisher=Academic Press |publication-place=New York |year=1981 |isbn=978-0-12-378520-6 |pages=102–105}}</ref>

Sea turtles orient themselves on land by night, using visual features detected in dim light. They can use their eyes in clear surface water, muddy coasts, the darkness of the deep ocean, and also above water. Unlike in terrestrial turtles, the [[cornea]] (the curved surface that lets light into the eye) does not help to focus light on the retina, so focusing underwater is handled entirely by the lens, behind the cornea. The cone cells contain oil droplets placed to shift perception toward the red part of the spectrum, improving color discrimination. Visual acuity, studied in hatchlings, is highest in a horizontal band with retinal cells packed about twice as densely as elsewhere. This gives the best vision along the visual horizon. Sea turtles do not appear to use [[polarized light]] for orientation as many other animals do. The deep-diving leatherback turtle lacks specific adaptations to low light, such as large eyes, large lenses, or a reflective [[Tapetum lucidum|tapetum]]. It may rely on seeing the [[bioluminescence]] of prey when hunting in deep water.<ref name="Fritsches et al 2013">{{cite book |last1=Fritsches |first1=Kerstin A. |last2=Warrant |first2=Eric J. |chapter=Vision |editor-last=Wyneken |editor-first=Jeanette |title=The Biology of Sea Turtles |publisher=CRC Press |year=2013 |isbn=978-1-4398-7308-3 |oclc=828509848 |pages=31–58}}</ref>

Turtles have no ear openings; the [[eardrum]] is covered with scales and encircled by a bony [[otic capsule]], which is absent in other reptiles.{{sfn|Orenstein|2012|p=36}} Their hearing thresholds are high in comparison to other reptiles, reaching up to 500 [[Hz]] in air, but underwater they are more attuned to lower frequencies.<ref>{{cite book|last=Willis|first=Katie L. |title=The Effects of Noise on Aquatic Life II |chapter=Underwater Hearing in Turtles |series=Advances in Experimental Medicine and Biology |year=2016 |volume=875 |pages=1229–1235 |doi=10.1007/978-1-4939-2981-8_154 |pmid=26611091|isbn=978-1-4939-2980-1 }}</ref> The [[loggerhead sea turtle]] has been shown experimentally to respond to low sounds, with maximal sensitivity between 100 and 400&nbsp;Hz.<ref name="MartinAlessi2012">{{cite journal |last1=Martin |first1=Kelly J. |last2=Alessi |first2=Sarah C. |last3=Gaspard |first3=Joseph C. |last4=Tucker |first4=Anton D. |last5=Bauer |first5=Gordon B. |last6=Mann |first6=David A. |title=Underwater Hearing in the Loggerhead Turtle (''Caretta caretta''): a Comparison of Behavioral and Auditory Evoked Potential Audiograms |journal=Journal of Experimental Biology |volume=215 |issue=17 |year=2012 |pages=3001–3009 |issn=1477-9145 |doi=10.1242/jeb.066324 |pmid=22875768 |s2cid=459652 |url=https://scholarcommons.usf.edu/etd/3233 |doi-access=free }}</ref>

Turtles have [[Olfactory system|olfactory]] (smell) and [[vomeronasal organ|vomeronasal]] receptors along the nasal cavity, the latter of which are used to detect chemical signals.{{sfn|Orenstein|2012|pp=35–36}} Experiments on green sea turtles showed they could learn to respond to a selection of different odorant chemicals such as [[triethylamine]] and [[cinnamaldehyde]], which were detected by olfaction in the nose. Such signals could be used in navigation.<ref name="MantonKarr1972">{{cite journal |last1=Manton |first1=Marion |last2=Karr |first2=Andrew |last3=Ehrenfeld |first3=David W. |title=Chemoreception in the Migratory Sea Turtle, ''Chelonia mydas'' |journal=The Biological Bulletin |volume=143 |issue=1 |year=1972 |pages=184–195 |issn=0006-3185 |doi=10.2307/1540338 |jstor=1540338 |url=https://www.biodiversitylibrary.org/part/24653 |access-date=June 6, 2021 |archive-date=June 6, 2021 |archive-url=https://web.archive.org/web/20210606225146/https://www.biodiversitylibrary.org/part/24653 |url-status=live }}</ref>