Editing Crocodile (section)

==Biology and behaviour==

Crocodilians are more closely related to birds and dinosaurs than to most animals classified as reptiles, the three families being included in the group [[Archosauria]] ('ruling reptiles'). Despite their prehistoric look, crocodiles are among the more biologically complex reptiles. Unlike other reptiles, a crocodile has a [[cerebral cortex]] and a four-chambered [[heart]]. Crocodilians also have the functional equivalent of a diaphragm by incorporating muscles used for aquatic locomotion into respiration.<ref name="Uriona & Farmer, 2008">{{cite journal|vauthors=Uriona TJ, Farmer CG |year=2008|title=Recruitment of the diaphragmaticus, ischiopubis and other respiratory muscles to control pitch and roll in the American alligator (''Alligator mississippiensis'') |journal=Journal of Experimental Biology|volume=211|pages=1141–1147|pmid=18344489|doi=10.1242/jeb.015339|issue=Pt 7|doi-access=free|bibcode=2008JExpB.211.1141U }}</ref> [[Salt gland]]s are present in the tongues of crocodiles and they have a pore opening on the surface of the tongue, a trait that separates them from alligators. Salt glands are dysfunctional in Alligatoridae.<ref name=ausfauna /> Their function appears to be similar to that of salt glands in [[marine turtle]]s. Crocodiles do not have sweat glands and release heat through their mouths. They often sleep with their mouths open and may pant like a dog.<ref>{{cite web | author= Anitai, Stefan | title = 14 Amazing Facts About Crocodiles – Living dinosaurs | date = 3 November 2007 | url=http://news.softpedia.com/news/14-Amazing-Facts-About-Crocodiles-69931.shtml | publisher= Softpedia | access-date = 1 April 2008}}</ref> Four species of freshwater crocodile climb trees to bask in areas lacking a shoreline.<ref>{{cite journal | url=http://www.herpetologynotes.seh-herpetology.org/Volume7_PDFs/Dinets_HerpetologyNotes_volume7_pages3-7.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.herpetologynotes.seh-herpetology.org/Volume7_PDFs/Dinets_HerpetologyNotes_volume7_pages3-7.pdf |archive-date=2022-10-09 |url-status=live | title=Climbing behaviour in extant crocodilians |author1=Dinets, Vladimir |author2=Britton, Adam |author3=Shirley, Matthew | journal=Herpetology Notes | year=2013 | volume=7 | pages=3–7}}</ref>

===Senses===
[[File:A crocodiles eye (7825799462).jpg|thumb|Crocodile eye]]
Crocodiles have acute senses, an evolutionary advantage that makes them successful predators. The eyes, ears and nostrils are located on top of the head, allowing the crocodile to lie low in the water, almost totally submerged and hidden from prey.

====Vision====
Crocodiles have very good night vision, and are mostly [[Nocturnality|nocturnal]] hunters. They use the disadvantage of most prey animals' poor nocturnal vision to their advantage. The light receptors in crocodilians' eyes include [[Cone cell|cones]] and numerous [[Rod cells|rods]], so it is assumed all crocodilians can see colours.<ref>{{cite web|url=http://wikis.evergreen.edu/m2o1112/index.php/Reptiles|title=Reptiles|author=evergreen|access-date=29 April 2013|archive-url=https://web.archive.org/web/20130615152003/http://wikis.evergreen.edu/m2o1112/index.php/Reptiles|archive-date=15 June 2013|url-status=dead}}</ref> Crocodiles have vertical-slit shaped pupils, similar to those of domestic cats. One explanation for the evolution of slit pupils is that they exclude light more effectively than a circular pupil, helping to protect the eyes during daylight.<ref name="Land, (2006)">{{cite journal | last1 = Land | first1 = M.F. | year = 2006 | title = Visual optics: the shapes of pupils | journal = Current Biology | volume = 16 | issue = 5| pages = R167–R168 | doi=10.1016/j.cub.2006.02.046 | pmid=16527734| doi-access = free | bibcode = 2006CBio...16.R167L }}</ref> On the rear wall of the eye is a [[tapetum lucidum]], which reflects incoming light back onto the retina, thus utilizing the small amount of light available at night to best advantage. In addition to the protection of the upper and lower eyelids, crocodiles have a [[nictitating membrane]] (sometimes called a "third eye-lid") that can be drawn over the eye from the inner corner while the lids are open. The eyeball surface is thus protected under the water while a certain degree of vision is still possible.<ref name="Encyclopædia Britannica">{{cite web|url=https://www.britannica.com/EBchecked/topic/143679/crocodile/38424/Form-and-function|title=Crocodile|author=Encyclopædia Britannica|access-date=29 April 2013}}</ref>

====Olfaction====
Crocodilian [[Olfaction|sense of smell]] is also very well developed, aiding them to detect prey or animal carcasses that are either on land or in water, from far away. It is possible that crocodiles use olfaction in the egg prior to hatching.<ref name="Encyclopædia Britannica" />

[[Chemoreception]] in crocodiles is especially interesting because they hunt in both terrestrial and aquatic surroundings. Crocodiles have only one olfactory chamber and the [[vomeronasal organ]] is absent in the adults<ref>{{cite journal | last1 = Hansen | first1 = A | year = 2007 | title = Olfactory and solitary chemosensory cells: two different chemosensory systems in the nasal cavity of the American alligator, Alligator mississippiensis | journal = BMC Neuroscience | volume = 8 | page = 64 | doi = 10.1186/1471-2202-8-64 | pmid = 17683564 | pmc = 1950884 | doi-access = free }}</ref> indicating all olfactory perception is limited to the olfactory system. Behavioural and olfactometer experiments indicate that crocodiles detect both air-borne and water-soluble chemicals and use their olfactory system for hunting. When above water, crocodiles enhance their ability to detect volatile odorants by gular pumping, a rhythmic movement of the floor of the pharynx.<ref>{{cite journal | last1 = Gans | first1 = C. | last2 = Clark | first2 = B. | year = 1976 | title = Studies on ventilation of Caiman crocodilus (Crocodilia: Reptilia) | url =https://deepblue.lib.umich.edu/bitstream/2027.42/21779/1/0000173.pdf | journal = Respir. Physiol | volume = 26 | issue = 3| pages = 285–301 | doi=10.1016/0034-5687(76)90001-3| pmid = 951534 | hdl = 2027.42/21779 | hdl-access = free }}</ref><ref>{{cite journal | last1 = Putterill | first1 = J.F. | last2 = Soley | first2 = J.T. | year = 2006 | title = Morphology of the gular valve of the Nile crocodile, Crocodylus niloticus (Laurenti, 1768) | journal = J. Morphol. | volume = 267 | issue = 8| pages = 924–939 | doi=10.1002/jmor.10448| pmid = 16634086 | s2cid = 21995436 }}</ref> Crocodiles close their nostrils when submerged, so olfaction underwater is unlikely. Underwater food detection is presumably gustatory and tactile.<ref>Schwenk, K. (2008). Comparative anatomy and physiology of chemical senses in nonavian aquatic reptiles. In, ''Sensory Evolution on the Threshold: Adaptations in Secondarily Aquatic Vertebrates''. J.G.M [[Hans Thewissen|Thewissen]] and S. Nummels (Eds). University of California Press, Berkeley. pp. 65–81</ref>

====Hearing====
Crocodiles can hear well; their [[Eardrum|tympanic membranes]] are concealed by flat flaps that may be raised or lowered by muscles.<ref name=ausfauna />

====Touch====
The touch sensors, concentrated in crocodile skin, can be thicker than those in human fingerprints.<ref>{{Cite web|date=9 November 2012|title=Croc Jaws More Sensitive Than Human Fingertips|url=https://www.nationalgeographic.com/animals/article/121108-nile-crocodile-duncan-leitch-science-human-sensitive-touch|archive-url=https://web.archive.org/web/20210325143141/https://www.nationalgeographic.com/animals/article/121108-nile-crocodile-duncan-leitch-science-human-sensitive-touch|url-status=dead|archive-date=25 March 2021|access-date=31 January 2022|website=Animals|language=en}}</ref> Crocodiles can feel the touch on their skin.<ref>{{Cite web|date=14 October 2021|title=Do Crocodiles Feel Pain? (Surprising Answer) {{!}}|url=https://wildexplained.com/do-crocodiles-feel-pain/|access-date=31 January 2022|language=en-us}}</ref>

'''Cranial''': The upper and lower jaws are covered with sensory pits, visible as small, black speckles on the skin, the crocodilian version of the [[lateral line]] organs seen in fish and many amphibians, though arising from a completely different origin. These pigmented nodules encase bundles of [[Axon|nerve fibers]] innervated beneath by branches of the trigeminal nerve. They respond to the slightest disturbance in surface water, detecting vibrations and small pressure changes as small as a single drop.<ref>{{cite news|url=https://www.cbc.ca/news/science/alligators-detect-silent-ripples-when-hunting-1.320458|title=Alligators detect silent ripples when hunting|author=CBCnews|year=2002|access-date=29 April 2013|work=CBC News}}</ref> This makes it possible for crocodiles to detect prey, danger and intruders, even in total darkness. These sense organs are known as domed pressure receptors (DPRs).<ref name="Jackson and Brooks">{{cite journal | last1 = Jackson | first1 = K. | last2 = Brooks | first2 = D.R. | year = 2007 | title = Do crocodiles co-opt their sense of "touch" to "taste"? A possible new type of vertebrate sensory organ | url = http://people.whitman.edu/~jacksok/AMRE2447.pdf | journal = Amphibia-Reptilia | volume = 28 | issue = 2 | pages = 277–285 | doi = 10.1163/156853807780202486 | access-date = 29 April 2013 | archive-url = https://web.archive.org/web/20130730091857/http://people.whitman.edu/~jacksok/AMRE2447.pdf | archive-date = 30 July 2013 | url-status = dead }}</ref>

'''Post-Cranial''': While alligators and caimans have DPRs only on their jaws, crocodiles have similar organs on almost every scale on their bodies. The function of the DPRs on the jaws is clear; to catch prey, but it is still not clear what the function is of the organs on the rest of the body. The receptors flatten when exposed to increased osmotic pressure, such as that experienced when swimming in sea water [[hyperosmotic]] to the body fluids. When contact between the integument and the surrounding sea water solution is blocked, crocodiles are found to lose their ability to discriminate salinities. It has been proposed that the flattening of the sensory organ in hyperosmotic sea water is sensed by the animal as "touch", but interpreted as chemical information about its surroundings.<ref name="Jackson and Brooks" /> This might be why in alligators they are absent on the rest of the body.<ref>{{cite web|url=http://crocodilian.com/cnhc/cbd-gb1.htm |title=Crocodilian Biology Database – Integumentary Sense Organs |publisher=Crocodilian.com |access-date=26 April 2013}}</ref>

===Hunting and diet===
[[File:Crocodile attack during Mara River crossing - frame 1 - Flickr - Lip Kee.jpg|thumb|Nile crocodile attacking wildebeest]]
[[File:Human Crocodile Conflict.jpg|thumb|An example of humans and mugger crocodiles in the same environment]]
[[File:Crocodile at Ranganathittu, Mysore, Karnataka.JPG|thumb|Even a cruising crocodile is difficult to locate]]
Crocodiles are [[ambush predator]]s, waiting for fish or land animals to come close, then rushing out to attack. Crocodiles mostly eat [[fish]], [[amphibian]]s, [[crustacean]]s, [[mollusc]]s, [[bird]]s, [[reptile]]s, and [[mammal]]s, and they occasionally [[cannibalize]] smaller crocodiles. What a crocodile eats varies greatly with species, size and age. From the mostly fish-eating species, like the [[Slender-snouted crocodile|slender-snouted]] and [[freshwater crocodile]]s, to the larger species like the [[Nile crocodile]] and the [[saltwater crocodile]] that prey on large mammals, such as [[Bovinae|buffalo]], [[deer]] and [[wild boar]], diet shows great diversity. Diet is also greatly affected by the size and age of the individual within the same species. All young crocodiles hunt mostly [[invertebrates]] and small [[fish]], gradually moving on to larger prey. Being [[ectotherm]]ic (cold-blooded) predators, they have a very slow [[metabolism]], so they can survive long periods without food. Despite their appearance of being slow, crocodiles have a very fast strike and are top [[predator]]s in their environment, and various species have been observed attacking and killing other [[predator]]s such as [[shark]]s and [[big cat]]s.<ref name = NGeographicCroc>{{cite web|url=https://www.nationalgeographic.com/animals/?nav=A-Z |title=Saltwater Crocodile, Saltwater Crocodile Profile, Facts, Information, Photos, Pictures, Sounds, Habitats, Reports, News – National Geographic |publisher=Animals.nationalgeographic.com |access-date=16 March 2010}}</ref><ref>{{cite web |url=http://crocodilian.com/cnhc/csp_cnil.htm |title=Crocodilian Species – Nile Crocodile (Crocodylus niloticus) |publisher=Crocodilian.com |access-date=26 April 2013 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025183255/http://crocodilian.com/cnhc/csp_cnil.htm |url-status=dead }}</ref> Crocodiles are also known to be aggressive [[scavenger]]s who feed upon [[carrion]] and steal from other predators.<ref>{{cite web|url=http://www.australiananimallearningzone.com/saltwater-crocodile-crocodylus-porosus.htm|title=Saltwater Crocodile Profile|work=Australian Animal|date=22 December 2012 }}</ref> Evidence suggests that crocodiles also feed upon fruits, based on the discovery of seeds in stools and stomachs from many subjects as well as accounts of them feeding.<ref>{{cite magazine|url=http://www.popsci.com/article/science/are-crocodiles-secret-fruit-lovers|title=ARE CROCODILES SECRET FRUIT-LOVERS?|magazine=[[Popular Science]]|author=Jon Tennant}} 13 November 2013</ref><ref>{{cite web|url=http://www.livescience.com/39198-crocodiles-alligators-eat-fruit.html?li_source=LI&li_medium=more-from-livescience|title=Crikey! Crocodiles and Alligators Snack on Fruit|work=[[Live Science]]|author=Charles Q. Choi|date=27 August 2013}} 27 August 2013</ref>

Crocodiles have the most acidic stomach of any vertebrate. They can easily digest bones, hooves and horns. The [[BBC TV]]<ref>BBC channel 1 program ''Inside The Perfect Predator'', Thursday 25 March 2010</ref> reported that a [[Nile crocodile]] that has lurked a long time underwater to catch prey builds up a large [[oxygen debt]]. When it has caught and eaten that prey, it closes its right [[aortic arch]] and uses its left aortic arch to flush blood loaded with [[carbon dioxide]] from its muscles directly to its stomach; the resulting excess acidity in its blood supply makes it much easier for the stomach lining to secrete more [[stomach acid]] to quickly dissolve bulks of swallowed prey flesh and bone. Many large crocodilians swallow stones (called gastroliths or stomach stones), which may act as ballast to balance their bodies or assist in crushing food,<ref name=ausfauna /> similar to grit ingested by birds. [[Herodotus]] claimed that Nile crocodiles had a [[symbiosis|symbiotic relationship]] with certain birds, such as the [[Egyptian plover]], which enter the crocodile's mouth and pick [[leech]]es feeding on the crocodile's blood; with no evidence of this interaction actually occurring in any crocodile species, it is most likely mythical or allegorical fiction.<ref>{{cite web |author=Adam Britton |url=http://crocodilian.blogspot.com/2009/09/crocodile-myths-1-curious-trochilus.html |title=Croc Blog: Crocodile myths #1 – the curious trochilus |publisher=Crocodilian.blogspot.com |date=6 September 2009 |access-date=26 April 2013 |archive-date=11 March 2013 |archive-url=https://web.archive.org/web/20130311082746/http://crocodilian.blogspot.com/2009/09/crocodile-myths-1-curious-trochilus.html |url-status=dead }}</ref>

====Bite====
[[File:Nile Crocodile (Crocodylus niloticus) trying to swallow a big Tilapia (Oreochromis sp.)... (16818888756).jpg|thumb|left|Nile crocodile trying to swallow a big [[Tilapia]] in [[Kruger National Park]], South Africa]]
Since they feed by grabbing and holding onto their prey, they have [[Evolution|evolved]] sharp teeth for piercing and holding onto flesh, and powerful muscles to close the jaws and hold them shut. The teeth are not well-suited to tearing flesh off of large prey items as are the dentition and claws of many mammalian carnivores, the hooked bills and talons of [[Bird of prey|raptorial birds]], or the serrated teeth of sharks. However, this is an advantage rather than a disadvantage to the crocodile since the properties of the teeth allow it to hold onto prey with the least possibility of the prey animal escaping. Cutting teeth, combined with the exceptionally high [[bite|bite force]], would pass through flesh easily enough to leave an escape opportunity for prey. The jaws can bite down with immense force, by far the strongest bite of any animal. The force of a large crocodile's bite is more than {{convert|5000|lbf|N|abbr=on}}, which was measured in a {{convert|5.5|m|ft|abbr=on}} [[Nile crocodile]], in the field;<ref>National Geographic documentary; "Bite Force", Brady Barr.</ref> comparing to {{convert|335|lbf|N|abbr=on}} for a [[Rottweiler]], {{convert|800|lbf|N|abbr=on}} for a [[hyena]], {{convert|2200|lbf|N|abbr=on}} for an [[American alligator]],<ref>{{cite web|url=http://dogfacts.wordpress.com/2008/02/03/national-geographics-dr-brady-barrs-bite-pressure-tests/ |title=National Geographic's Dr. Brady Barr's Bite Pressure Tests &#124; Dog Facts |publisher=Dogfacts.wordpress.com |access-date=26 April 2013|date=3 February 2008 }}</ref>{{failed verification|date=October 2014}} and {{convert|4095|lbf|N|abbr=on}} for the largest confirmed [[great white shark]].<ref name="GWB">{{cite journal|last=Wroe|first=S.|author2=Huber, D. R.|author3=Lowry, M.|author4=McHenry, C.|author5=Moreno, K.|author6=Clausen, P.|author7=Ferrara, T. L.|author8=Cunningham, E.|author9=Dean, M. N. |author10= Summers, A. P.|title=Three-dimensional computer analysis of white shark jaw mechanics: how hard can a great white bite?|url=http://www.bio-nica.info/Biblioteca/Wroe2008GreatWhiteSharkBiteForce.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.bio-nica.info/Biblioteca/Wroe2008GreatWhiteSharkBiteForce.pdf |archive-date=2022-10-09 |url-status=live|journal=Journal of Zoology|volume=276|issue=4|pages=336–342|year= 2008|doi=10.1111/j.1469-7998.2008.00494.x}}</ref>

A {{convert|5.2|m|ft|abbr=on}} long saltwater crocodile has been confirmed as having the strongest [[bite|bite force]] ever recorded for an animal in a laboratory setting. It was able to apply a bite force value of {{convert|3700|lbf|N|abbr=on}}, and thus surpassed the previous record of {{convert|2125|lbf|N|abbr=on}} made by a {{convert|3.9|m|ft|abbr=on}} long [[American alligator]].<ref name="lappin">{{cite journal|title=The ontogeny of bite-force performance in American alligator (Alligator mississippiensis)|journal=[[Journal of Zoology]]|volume=260|issue=3|pages=317–327|url=http://www.alligatorfarm.us/images/Research/Erickson%20et%20al.%202003.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.alligatorfarm.us/images/Research/Erickson%20et%20al.%202003.pdf |archive-date=2022-10-09 |url-status=live|doi=10.1017/S0952836903003819|year=2003|last1=Erickson|first1=Gregory M.|last2=Lappin|first2=A. Kristopher|last3=Vliet|first3=Kent A.}}</ref><ref>{{cite journal|url=https://www.sciencedaily.com/releases/2012/03/120316093427.htm|title=Australian saltwater crocodiles are world's most powerful biters |journal=PLOS ONE |volume=7 |issue=3 |pages=e31781 |doi=10.1371/journal.pone.0031781 |pmid=22431965 |pmc=3303775 |date=16 March 2012 |access-date=26 April 2013|bibcode=2012PLoSO...731781E|last1=Erickson |first1=Gregory M. |last2=Gignac |first2=Paul M. |last3=Steppan |first3=Scott J. |last4=Lappin |first4=A. Kristopher |last5=Vliet |first5=Kent A. |last6=Brueggen |first6=John D. |last7=Inouye |first7=Brian D. |last8=Kledzik |first8=David |last9=Webb |first9=Grahame J. W. |doi-access=free }}</ref> Taking the measurements of several {{convert|5.2|m|ft|abbr=on}} crocodiles as reference, the bite forces of 6-m individuals were estimated at {{convert|7700|lbf|N|abbr=on}}.<ref name=autogenerated1>{{cite web|url=http://news.nationalgeographic.com/news/2012/03/120315-crocodiles-bite-force-erickson-science-plos-one-strongest/ |archive-url=https://web.archive.org/web/20120317064400/http://news.nationalgeographic.com/news/2012/03/120315-crocodiles-bite-force-erickson-science-plos-one-strongest/ |url-status=dead |archive-date=17 March 2012 |title=Crocodiles Have Strongest Bite Ever Measured, Hands-on Tests Show |publisher=News.nationalgeographic.com |date=15 March 2012 |access-date=26 April 2013}}</ref> The study, led by Dr. [[Gregory M. Erickson]], also shed light on the larger, [[extinct]] species of [[crocodilian]]s. Since crocodile [[anatomy]] has changed only slightly over the last 80 million years, current data on modern crocodilians can be used to estimate the bite force of extinct species. An {{convert|11|to(-)|12|m|ft|adj=on}} [[Deinosuchus]] would apply a force of {{convert|23100|lbf|N|abbr=on}}, nearly twice that of the latest, higher bite force estimations of [[Tyrannosaurus]] ({{convert|12814|lbf|N|abbr=on}}).<ref name="nationalgeographic1" /><ref name="FalkinghamBatesBiteforce2012">{{cite web|url=http://www.smithsonianmag.com/science-nature/The-Tyrannosaurus-Rexs-Dangerous-and-Deadly-Bite-37252918/|title=The Tyrannosaurus Rex's Dangerous and Deadly Bite|website=[[Smithsonian (magazine)|Smithsonian]]|date=October 2012|first=Riley|last=Black|access-date=6 June 2021}}</ref><ref name="BatesFalkingham2012">{{Cite journal|last1=Bates|first1=K. T.|last2=Falkingham|first2=P.L.|date=29 February 2012|title=Estimating maximum bite performance in Tyrannosaurus rex using multi-body dynamics|journal=Biology Letters|volume=8|issue=4|pages=660–664|doi=10.1098/rsbl.2012.0056|pmid=22378742|pmc=3391458}}</ref><ref>Crispian Scully, (2002) ''Oxford Handbook of Applied Dental Sciences'', Oxford University Press –{{ISBN|978-0-19-851096-3}} P156</ref> The extraordinary bite of crocodilians is a result of their [[anatomy]]. The space for the jaw muscle in the [[skull]] is very large, which is easily visible from the outside as a bulge at each side. The [[muscle]] is so stiff, it is almost as hard as bone to touch, as if it were the continuum of the skull. Another trait is that most of the muscle in a crocodile's jaw is arranged for clamping down. Despite the strong muscles to close the jaw, crocodiles have extremely small and weak muscles to open the jaw. Crocodiles can thus be subdued for study or transport by [[duct tape|taping]] their jaws or holding their jaws shut with large [[rubber band]]s cut from automobile [[tire|inner tube]]s.

===Locomotion===
[[File:Crocodile farm in Mexico.JPG|thumb|A crocodile, in a farm, gaping to thermoregulate]]
Crocodiles can move quickly over short distances, even out of water. The [[land speed]] record for a crocodile is {{convert|17|km/h|0|abbr=on}} measured in a galloping [[Freshwater crocodile|Australian freshwater crocodile]].<ref>{{cite web | last = Britton | first = Adam | title = Crocodilian Biology Database FAQ, "How fast can a crocodile run?" | url=http://www.flmnh.ufl.edu/cnhc/cbd-faq-q4.htm | access-date = 2 February 2008}}</ref> Maximum speed varies between species. Some species can gallop, including Cuban crocodiles, Johnston's crocodiles, New Guinea crocodiles, [[Dwarf crocodile|African dwarf crocodiles]], and even small [[Nile crocodiles]]. The fastest means by which most species can move is a "belly run", in which the body moves in a snake-like (sinusoidal) fashion, limbs splayed out to either side paddling away frantically while the tail whips to and fro. Crocodiles can reach speeds of {{convert|10|-|11|km/h|0|abbr=on}} when they "belly run", and often faster if slipping down muddy riverbanks. When a crocodile walks quickly, it holds its legs in a straighter and more upright position under its body, which is called the "high walk". This walk allows a speed of up to 5&nbsp;km/h.<ref>{{cite book|last1=Walters|first1=Martin|last2=Johnson|first2=Jinny|title=Encyclopedia of Animals|publisher=Marks and Spencer p.l.c|isbn=978-1-84273-964-8|page=145}}</ref>

Crocodiles may possess a [[homing instinct]]. In northern Australia, three rogue saltwater crocodiles were relocated {{convert|400|km|0|abbr=on}} by [[helicopter]], but returned to their original locations within three weeks, based on data obtained from tracking devices attached to them.<ref>{{cite journal|author=Read M. A.|author2=Grigg G. C.|author3=Irwin S. R.|author4=Shanahan D.|author5=Franklin C. E. |year=2007 |title=Satellite Tracking Reveals Long Distance Coastal Travel and Homing by Translocated Estuarine Crocodiles, ''Crocodylus porosus'' |journal= PLOS ONE |volume=2 |issue=9 |page=e949 |doi=10.1371/journal.pone.0000949 |editor1-last=Lusseau |editor1-first=David |pmid=17895990 |pmc=1978533|bibcode=2007PLoSO...2..949R|doi-access=free}}</ref>

===Longevity===
Measuring crocodile age is unreliable, although several techniques are used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth—each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons.<ref>{{cite web|url=http://www.flmnh.ufl.edu/cnhc/cbd-faq-q3.htm |title=Crocodilian Biology Database, FAQ. "How long do crocodiles live for?" |publisher=Flmnh.ufl.edu |access-date=26 April 2013}}</ref> Bearing these inaccuracies in mind, it can be safely said that all crocodile species have an average lifespan of at least 30–40 years, and in the case of larger species an average of 60–70 years. The oldest crocodiles appear to be the largest species. [[Saltwater crocodile|''C. porosus'']] is estimated to live around 70 years on average, with limited evidence of some individuals exceeding 100 years.<ref>{{cite web |url=http://crocodilian.com/cnhc/cbd-faq-q3.htm |title=Crocodilian Biology Database – FAQ – How long do crocodiles live for? |publisher=Crocodilian.com |access-date=26 April 2013 |archive-date=21 March 2015 |archive-url=https://web.archive.org/web/20150321151949/http://crocodilian.com/cnhc/cbd-faq-q3.htm |url-status=dead }}</ref>

In captivity, some individuals are claimed to have lived for over a century. A male crocodile lived to an estimated age of 110–115 years in a Russian zoo in [[Yekaterinburg]].<ref name=yeka /> Named Kolya, he joined the zoo around 1913 to 1915, fully grown, after touring in an animal show, and lived until 1995.<ref name=yeka>{{cite news | agency=Associated Press | title=Crocodile at Russian zoo dies; on display since czars | date=16 February 1995 | work=The News–Journal | location=Daytona Beach, Florida | volume=70 | issue=47 | publisher=News–Journal Corporation | url=https://news.google.com/newspapers?nid=1901&dat=19950216&id=MqgtAAAAIBAJ&pg=2827,36264 }}</ref> A male freshwater crocodile lived to an estimated age of 120–140 years at the [[Australia Zoo]].<ref name=campbell2010>{{cite news | title=Freshie the croc dies at age 140 | first=Kieran | last=Campbell | date=24 March 2010 | url=http://www.sunshinecoastdaily.com.au/news/freshie-the-croc-dies-at-age-140/494141/ | work=Sunshine Coast Daily }}</ref> Known affectionately as "Mr. Freshie", he was rescued around 1970 by [[Bob Irwin]] and [[Steve Irwin]], after being shot twice by hunters and losing an eye as a result, and lived until 2010.<ref name=campbell2010 /> Crocworld Conservation Centre, in [[Scottburgh]], South Africa, claims to have a male [[Nile crocodile]] that was born in 1900. Named Henry, the crocodile is said to have lived in [[Botswana]] along the [[Okavango River]], according to centre director Martin Rodrigues.<ref>{{cite web|url=http://ibnlive.in.com/news/johannesburg-worlds-oldest-crocodile-turns-114/518422-2.html |archive-url=https://web.archive.org/web/20141217215908/http://ibnlive.in.com/news/johannesburg-worlds-oldest-crocodile-turns-114/518422-2.html |url-status=dead |archive-date=17 December 2014 |title=Johannesburg: World's oldest crocodile turns 114 |publisher=IBN Live |date=16 December 2014| access-date=19 December 2014}}</ref><ref>{{cite news |url=http://www.elnuevodia.com/celebrancumpleanosdelcocodrilomaslongevodelmundo-1911287.html |title=Celebran cumpleaños del cocodrilo más longevo del mundo |newspaper=[[El Nuevo Día]] |date=16 December 2014 |access-date=19 December 2014 |archive-date=21 December 2014 |archive-url=https://web.archive.org/web/20141221220518/http://www.elnuevodia.com/celebrancumpleanosdelcocodrilomaslongevodelmundo-1911287.html |url-status=dead }}</ref>

===Social behaviour and vocalization===
[[File:Crocodiles resting together.jpeg|thumbnail|right|Captive crocodiles resting together with open jaws.]]
Crocodiles are the most social of reptiles. Even though they do not form social groups, many species congregate in certain sections of [[river]]s, tolerating each other at times of [[feeding]] and [[Body temperature|basking]]. Most species are not highly territorial, with the exception of the saltwater crocodile, which is a highly [[territory (animal)|territorial]] and aggressive species: a mature, male saltwater crocodile will not tolerate any other males at any time of the year, but most other species are more flexible. There is a certain form of [[hierarchy]] in crocodiles: the largest and heaviest males are at the top, having access to the best basking site, while females are priority during a group feeding of a big kill or carcass. A good example of the hierarchy in crocodiles would be the case of the [[Nile crocodile]]. This species clearly displays all of these behaviours. Studies in this area are not thorough, however, and many species are yet to be studied in greater detail.<ref>{{cite web |url=http://crocodilian.com/cnhc/csp_cnil.htm |title=Crocodilian Species List |publisher=Crocodilian.com |access-date=26 April 2013 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025183255/http://crocodilian.com/cnhc/csp_cnil.htm |url-status=dead }}</ref> [[Mugger crocodile]]s are also known to show toleration in group feedings and tend to congregate in certain areas. However, males of all species are aggressive towards each other during mating season, to gain access to females.

Crocodiles are also the most vocal of all reptiles, producing a wide variety of sounds during various situations and conditions, depending on species, age, size and sex. Depending on the context, some species can communicate over 20 different messages through [[Animal communication|vocalizations]] alone.<ref>{{cite web|url=http://crocodilian.com/cnhc/croccomm.html |title=Crocodilian Communication |publisher=Crocodilian.com |access-date=29 April 2013}}</ref> Some of these vocalizations are made during social communication, especially during [[territory (animal)|territorial]] displays towards the same sex and [[courtship display|courtship]] with the opposite sex; the common concern being [[reproduction]]. Therefore most [[conspecific]] vocalization is made during the [[breeding season]], with the exception being year-round [[territorial behaviour]] in some species and quarrels during feeding. Crocodiles also produce different distress calls and in aggressive displays to their own kind and other animals; notably other predators during [[Interspecific competition|interspecific]] predatory confrontations over carcasses and terrestrial kills.

Specific vocalisations include&nbsp;—

* '''Chirp''': When about to hatch, the young make a "peeping" noise, which encourages the female to excavate the nest. The female then gathers the hatchlings in her mouth and transports them to the water, where they remain in a group for several months, protected by the female<ref>{{cite web|url=http://www.arkive.org/nile-crocodile/crocodylus-niloticus/|archive-url=https://web.archive.org/web/20090123041108/http://www.arkive.org/nile-crocodile/crocodylus-niloticus/|url-status=dead|archive-date=23 January 2009|author=Arkive|title=Nile crocodile (''Crocodylus niloticus'')|access-date=29 April 2013}}</ref>
* '''Distress call''': A high-pitched call used mostly by younger animals to alert other crocodiles to imminent danger or an animal being attacked.
* '''Threat call''': A hissing sound that has also been described as a coughing noise.
* '''Hatching call''': Emitted by a female when breeding to alert other crocodiles that she has laid eggs in her nest.
* '''Bellowing''': Male crocodiles are especially vociferous. Bellowing choruses occur most often in the spring when breeding groups congregate, but can occur at any time of year. To bellow, males noticeably inflate as they raise the tail and head out of water, slowly waving the tail back and forth. They then puff out the throat and with a closed mouth, begin to vibrate air. Just before bellowing, males project an [[infrasonic]] signal at about 10&nbsp;Hz through the water, which vibrates the ground and nearby objects. These low-frequency vibrations travel great distances through both air and water to advertise the male's presence and are so powerful they result in the water's appearing to "dance".<ref>{{cite web |url=http://factsanddetails.com/Asian.php?itemid=2435&subcatid=434 |archive-url=https://archive.today/20130629045148/http://factsanddetails.com/Asian.php?itemid=2435&subcatid=434 |url-status=dead |archive-date=29 June 2013 |author=Hays, J. |title=Crocodiles: Their history, characteristics and behavior |year=2008 |access-date=31 May 2013 }}</ref>

===Reproduction===
====Mating====
[[File:Nile crocodile eggs.jpg|thumb|Crocodile eggs]]
[[courtship display|Courtship]] takes place in a series of behavioural interactions that include a variety of snout rubbing and submissive display that can take a long time. Mating always takes place in water, where the pair can be observed mating several times.<ref name="autogenerated2000"/>

====Egg-laying & nesting====
[[Egg]]-laying usually takes place at night and about 30–40 minutes, which are laid in either holes or mound [[nest]]s, depending on species.<ref name="autogenerated2000"/>  The eggs are hard shelled, but translucent at the time of egg-laying. Depending on the species of crocodile, 7 to 95 eggs are laid. <ref name=webb/> [[Scute]]s may play a role in calcium storage for eggshell formation.<ref name=":0" />   

[[Nest]]ing periods range from a few weeks up to six months. A hole nest is usually excavated in sand and a mound nest is usually constructed out of vegetation. Females can build or dig several trial nests which appear incomplete and abandoned later. <ref name="autogenerated2000">{{cite book |author1=K. Richardson |author2=G. Webb |author3=C. Manolis |title = Crocodiles: Inside and Out |year = 2000}}</ref> Females are highly protective of their nests and young. Crocodile [[embryo]]s do not have sex chromosomes, and unlike humans, sex is not determined genetically. [[Temperature-dependent sex determination|Sex is determined by temperature]], where at {{convert|30|°C|0|abbr=on}} or less most hatchlings are females and at {{convert|31|°C|0|abbr=on}}, offspring are of both sexes. A temperature of {{convert|32|to|33|°C|0|abbr=on}} gives mostly males whereas above {{convert|33|°C|0|abbr=on}} in some species continues to give males, but in other species resulting in females, which are sometimes called high-temperature females.<ref name=webb>{{cite book |author1=G. Webb |author2=C. Manolis |title = Crocodiles of Australia |year = 1989}}</ref> Temperature also affects growth and survival rate of the young, which may explain the [[sexual dimorphism]] in crocodiles. The average [[incubation period]] is around 80 days, and also is dependent on temperature and species that usually ranges from 65 to 95 days. The eggshell structure is very conservative through evolution but there are enough changes to tell different species apart by their eggshell microstructure.<ref>{{cite journal | last1 = Marzola | first1 = M. | last2 = Russo | first2 = J. | last3 = Mateus | first3 = O. | year = 2015 | title = Identification and comparison of modern and fossil crocodilian eggs and eggshell structures | journal = Historical Biology | volume = 27 | issue = 1| pages = 115–133 | doi=10.1080/08912963.2013.871009| bibcode = 2015HBio...27..115M | s2cid = 85685470 }}</ref> 

At the time of hatching, the young start calling within the eggs. They have an [[egg-tooth]] at the tip of their snouts, which is developed from the skin, and that helps them pierce out of the shell. Hearing the calls, the female usually excavates the nest and sometimes takes the unhatched eggs in her mouth, slowly rolling the eggs to help the process. The young is usually carried to the water in the mouth. She would then introduce her hatchlings to the water and even feed them.<ref>{{cite web|url=http://scienceblogs.com/tetrapodzoology/2008/11/08/crocs-feed-their-babies/|title=Do crocodilians (sometimes) feed their young?|publisher=Science Blogs|author=Darren Naish}} 8 November 2008</ref> The mother would then take care of her young for over a year before the next mating season. In the absence of the mother crocodile, the father would act in her place to take care of the young.<ref>{{cite web|url=http://oddstuffmagazine.com/10-delightful-baby-animals-that-grow-up-to-be-fatal-predators.html|title=10 Delightful Baby Animals that Grow up to Be Fatal Predators|date=3 February 2012|publisher=Odd Stuff}} 3 February 2012</ref> However, even with a sophisticated [[Paternal care|parental nurturing]], young crocodiles have a very high mortality rate due to their vulnerability to predation.<ref>{{cite web|url=http://animals.mom.me/life-cycle-alligators-crocodiles-8058.html|title=THE LIFE CYCLE OF ALLIGATORS AND CROCODILES|publisher=Demand Media|author= Jasey Kelly}}</ref> A group of [[hatchling]]s is called a pod or [[Crèche (zoology)|crèche]] and may be protected for months.<ref name="autogenerated2000" />

===Cognition===
Crocodiles possess some advanced cognitive abilities.<ref name="LA">{{cite news|url=https://www.latimes.com/science/sciencenow/la-sci-sn-clever-crocodiles-alligators-sticks-twigs-birds-lure-prey-20131206-story.html|title=Scary smart! Clever crocodiles, alligators use sticks to lure prey|author=Amina Khan|newspaper=Los Angeles Times|date=6 December 2013}} 6 December 2013</ref><ref name="Wash">{{cite news|url=https://www.washingtonpost.com/national/health-science/crocodiles-and-their-ilk-may-be-smarter-than-they-look/2013/12/06/1084cf28-5d2c-11e3-bc56-c6ca94801fac_story.html|title=Crocodiles and their ilk may be smarter than they look|newspaper=[[The Washington Post]]|author=Jason G. Goldman}} 9 December 2013</ref> Crocodiles [[cooperative hunting|cooperatively hunt]]. <ref name="One">{{cite web|url=http://www.oneworldmagazine.org/tales/crocs/smart.html|archive-url=https://web.archive.org/web/20000930224445/http://www.oneworldmagazine.org/tales/crocs/smart.html|url-status=dead|archive-date=30 September 2000|title=The Crocodile Files|work=One World Magazine}}</ref> Large numbers of crocodiles swim in circles to trap fish and take turns snatching them. In hunting larger prey, crocodiles swarm in, with one holding the prey down as the others rip it apart.

[[Vladimir Dinets]] of the [[University of Tennessee]], observing crocodile's use of [[Tool use by animals#In reptiles|twigs as bait]] was inconclusive. <ref>{{Cite journal|last1=Dinets|first1=Vladimir |last2=Brueggen
|first2=J.C. |last3=Brueggen
|first3=J.D.  |url=https://www.researchgate.net/publication/271994159|date=December 2013|title=Crocodilians use tools for hunting|journal=[[Ethology Ecology & Evolution]]|volume=27|issue=1|pages=74–78|publisher= www.[[researchgate]].net|doi=10.1080/03949370.2013.858276}}
</ref>