Editing Hippopotamus (section)

==Behaviour and ecology==
[[File:Hippo.ogv|thumb|right|Video of hippos in the wild]]
Hippos are [[semiaquatic]] and require enough water to immerse in, while being close to grass.<ref name=estes/> They mostly live in freshwater habitat, but can be found in [[estuaries]].<ref name=iucn/> They prefer relatively still waters with gently sloping shores, though male hippos may also be found in very small numbers in more [[Rapids|rapid]] waters with rocky slopes.<ref name=kingdon/>{{rp|264}} Like most herbivores, hippos will consume a variety of plants if presented with them in captivity, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants.<ref name="Grey"/> Hippos spend most of the day in water to stay cool and hydrated. Just before night begins, they leave the water to forage on land. A hippo will travel {{cvt|3|–|5|km}} per night, eating around {{cvt|40|kg}} of grass. By dawn, they are back in the water.<ref name=estes/>

Despite being semiaquatic, an adult hippo is not a particularly good swimmer, nor can it float. It rarely enters deep water; when it does, the animal moves by bouncing off the bottom. An adult hippo surfaces every four to six minutes, while young need to breathe every two to three minutes.<ref name="The Hippos"/>{{rp|3–4}} Hippos move on land by [[trot]]ting, and limb movements do not change between speeds. They can reach an airborne stage (a stage when all limb are off the ground) when they move fast enough. Hippos are reported to reach {{cvt|30|km/h}} but this has not been confirmed.<ref>{{cite journal|last1=Hutchinson|first1=J. R.|last2=Pringle|first2=E. V.|year=2024|title=Footfall patterns and stride parameters of Common hippopotamus (''Hippopotamus amphibius'') on land|journal=PeerJ|volume=12|page=e17675|doi=10.7717/peerj.17675|doi-access=free |pmid=38974416 |pmc=11227274}}</ref> They are incapable of jumping but can walk up steep banks.<ref name=estes/> The hippopotamus sleeps with both hemispheres of the brain resting, as in all land mammals, and usually sleeps on land or in water with the nostrils exposed. Despite this, it may be capable of sleeping while submerged, intermittently surfacing to breathe without waking. They appear to transition between different phases of sleep more quickly than other mammals.<ref>{{cite journal|author1=Dell, Leigh-Anne|author2=Patzke, Nina|author3=Spocter, Muhammad A.|author4=Bertelsen, Mads F.|author5=Siegel, Jerome M.|author6=Manger, Paul R.|year=2016|title=Organization of the sleep-related neural systems in the brain of the river hippopotamus (''Hippopotamus amphibius''): A most unusual cetartiodactyl species|journal=Journal of Comparative Neurology|volume=524|issue=10|pages=2036–2058|doi=10.1002/cne.23930|pmid=26588600 |pmc=8716328 }}</ref>

Because of their size and their habit of taking the same paths to feed, hippos can have a significant impact on the land across which they walk, keeping the land clear of vegetation and depressing the ground. Over prolonged periods, hippos can divert the paths of swamps and channels.<ref name="Botswana">{{Cite journal|journal = African Journal of Ecology|volume = 36|issue = 1|pages = 44–56|year = 1998|author1=McCarthy, T. S. |author2=Ellery, W. N. |author3=Bloem, A |title = Some observations on the geomorphological impact of hippopotamus (''Hippopotamus amphibius'' L.) in the Okavango Delta, Botswana|doi = 10.1046/j.1365-2028.1998.89-89089.x| bibcode=1998AfJEc..36...44M }}</ref> By defecating in the water, the animals also appear to pass on microbes from their gut, affecting the [[biogeochemical cycle]].<ref>{{cite journal|author1=Dutton, C. L.|author2=Subalusky, A. L.|author3=Sanchez, A.|author4=Estrela, S.|author5=Lu, N.|author6=Hamilton, S. K.|author7=Njoroge, L.|author8=Rosi, E. J.|author9=Post, D. M.|year=2021|title=The meta-gut: community coalescence of animal gut and environmental microbiomes|journal=Scientific Reports|volume=11|issue=1|page=23117|doi=10.1038/s41598-021-02349-1|pmid=34848778 |pmc=8633035 |bibcode=2021NatSR..1123117D }}</ref> On occasion, hippos have been filmed eating [[carrion]], usually near the water. There are other reports of meat-eating and even [[cannibalism]] and [[predation]].<ref>{{Cite journal|title = Reports of carnivory by the common hippo ''Hippopotamus amphibius''|author = Dudley, J. P.|journal = South African Journal of Wildlife Research| date=January 1998 |volume = 28|issue = 2|pages = 58–59|url = https://journals.co.za/content/wild/28/2/EJC117046}}</ref> Hippos' stomach anatomy lacks adaptions to carnivory and meat-eating is likely caused by lack of nutrients or just an abnormal behaviour.<ref name="The Hippos"/>{{rp|82–84}}

===Social life===
[[File:Hippo pod edit.jpg|thumb|right|Hippopotamus pod]]
It is challenging to study the interaction of bulls and cows because hippos are not [[Sexual dimorphism|sexually dimorphic]], so cows and young bulls are almost indistinguishable in the field.<ref>{{Cite journal |journal=[[African Zoology]] |volume=37 |issue=2 |author1=Beckwitt, R. |author2=Shea, J. |author3=Osborne, D. |author4=Krueger, S. |author5=Barklow, W. |year=2002 |title=A PCR-based method for sex identification in ''Hippopotamus amphibius'' |pages=127–130 |url=http://www.framingham.edu/~rbeckwitt/hippo2002.pdf |url-status=dead |archive-url=https://web.archive.org/web/20100617172906/http://www.framingham.edu/~rbeckwitt/hippo2002.pdf |archive-date=17 June 2010 |doi=10.1080/15627020.2002.11657167 |s2cid=88102117 }}</ref> Hippo pods fluctuate but can contain over 100 hippos. Although they lie close together, adults develop almost no social bonds. Males establish [[Territory (animal)|territories]] in water but not land, and these may range {{cvt|250|–|500|m}} in lakes and {{cvt|50|–|100|m}} in rivers. Territories are abandoned when the water dries up. The bull has breeding access to all the cows in his territory. Younger bachelors are allowed to stay as long as they defer to him. A younger male may challenge the old bull for control of the territory. Within the pods, the hippos tend to segregate by sex and status. Bachelor males lounge near other bachelors, females with other females, and the territorial male is on his own. When hippos emerge from the water to graze, they do so individually.<ref name="The Hippos"/>{{rp|4–5, 49–50}}

[[File:Hippo fight.jpg|thumb|left|Male hippos fighting]]
Hippos engage in "muck-spreading" which involves defecating while spinning their tails to distribute the faeces over a greater area. Muck-spreading occurs both on land and in water and its function is not well understood. It is unlikely to serve a territorial function, as the animals only establish territories in the water. They may be used as trails between the water and grazing areas.<ref name="The Hippos"/>{{rp|5, 51–52}} "Yawning" serves as a threat display.<ref name=estes/> When fighting, bulls use their incisors to block each other's attacks and their large canines as offensive weapons.<ref name=kingdon/>{{rp|259–260}} When hippos become over-populated or a habitat shrinks, bulls sometimes attempt [[Infanticide (zoology)|infanticide]], but this behaviour is not common under normal conditions.<ref name="Infanticide"/>

The most common hippo vocalisation is the "wheeze honk", which can travel over long distances in air.<ref name=wheeze-honk/> This call starts as a high-pitched squeal followed by a deeper, resonant call.<ref name="The Hippos"/>{{rp|5}} The animals can recognise the calls of other individuals. Hippos are more likely to react to the wheeze honks of strangers than to those they are more familiar with.<ref name=wheeze-honk>{{cite journal|last1=Thévenet|first1=J.|last2=Grimault|first2=N.|last3=Fonseca|first3=P.|last4=Mathevon|first4=N.|year=2022|title=Voice-mediated interactions in a megaherbivore|journal=Current Biology|volume=32|issue=2|pages=R70–R71|doi=10.1016/j.cub.2021.12.017|pmid=35077689 |bibcode=2022CBio...32..R70T |s2cid=246242737 |url=https://hal.archives-ouvertes.fr/hal-03543609/file/Pre-Print-CURRENT-BIOLOGY.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://hal.archives-ouvertes.fr/hal-03543609/file/Pre-Print-CURRENT-BIOLOGY.pdf |archive-date=2022-10-09 |url-status=live }}</ref> When threatened or alarmed, they produce exhalations,<ref name=estes/> and fighting bulls will bellow loudly.<ref name="The Hippos"/>{{rp|5}} Hippos are recorded to produce clicks underwater which may have [[Animal echolocation|echolocative]] properties.<ref>{{cite journal|last1=Maust-Mohl|first1=M|last2=Soltis|first2=J|last3= Reiss|first3=D|year=2018|title=Underwater click train production by the hippopotamus (''Hippopotamus amphibius'') suggests an echo-ranging function|journal=Behaviour|volume=155|issue=2–3|pages=231–251|doi=10.1163/1568539X-00003484|jstor=26488527}}</ref> They have the unique ability to hold their heads partially above the water and send out a cry that travels through both water and air; individuals respond both above and below water.<ref>{{Cite journal|title = Low-frequency sounds and amphibious communication in ''Hippopotamus amphibious''|url = http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JASMAN000115000005002555000001&idtype=cvips&gifs=yes|journal = The Journal of the Acoustical Society of America|author = Barklow, William E.|year = 2004|volume = 115|issue = 5|page = 2555|doi=10.1121/1.4783854|bibcode = 2004ASAJ..115.2555B}}</ref>

===Reproduction===
[[File:Mother and Young Hippo, Uganda (15397037561).jpg|thumb|right|Cow and calf]]
Cows reach sexual maturity at five to six years of age and have a [[pregnancy (mammals)|gestation period]] of eight months.<ref>{{cite journal|last1=Brown|first1=C. Emerson|title=Rearing Hippopotamuses in Captivity|journal=Journal of Mammalogy|date=November 1924|volume=5|issue=4|pages=243–246|doi=10.2307/1373731|jstor=1373731}}</ref> A study of [[endocrine system]]s revealed cows may begin puberty at as early as three or four years.<ref name="Endocrine">{{Cite journal|title = Endocrine patterns associated with reproduction in the Nile hippopotamus (''Hippopotamus amphibius'') as assessed by fecal progestagen analysis|journal=General and Comparative Endocrinology|volume=128|issue=1|year=2002|pages=74–81|author1=Graham, L. H.|author2= Reid, K. |author3=Webster, T. |author4=Richards, M. |author5=Joseph, S. |doi=10.1016/S0016-6480(02)00066-7|pmid = 12270790}}</ref> Bulls reach maturity at around 7.5 years. Both conceptions and births are highest during the [[wet season]]. Male hippos always have mobile [[spermatozoa]] and can breed year-round.<ref name="The Hippos"/>{{rp|59–61, 66}} After becoming pregnant, a female hippo will typically not begin ovulation again for 17 months.<ref name="Endocrine"/> Hippos mate in the water, with the cow remaining under the surface,<ref name="The Hippos"/>{{rp|63}} her head emerging periodically to draw breath. Cows  give birth in seclusion and return within 10 to 14 days. Calves are born on land or shallow water<ref name=estes/> weighing on average {{cvt|50|kg}} and at an average length of around {{cvt|127|cm}}. The female lies on her side when nursing, which can occur underwater or on land. The young are carried on their mothers' backs in deep water.<ref name="The Hippos"/>{{rp|4, 64}}

Mother hippos are very protective of their young, not allowing others to get too close.<ref name=estes/> One cow was recorded protecting a calf's carcass after it had died.<ref>{{cite journal|author1=Inman, V. L.|author2=Leggett, K. E. A.|year=2020|title=Observations on the response of a pod of hippos to a dead juvenile hippo (''Hippopotamus amphibius'', Linnaeus 1758)|journal=African Journal of Ecology|volume=58|issue=1|pages=123–125|doi=10.1111/aje.12644|bibcode=2020AfJEc..58..123I |s2cid=191169281 }}</ref> Calves may be temporarily kept in [[Crèche (zoology)|nurseries]], guarded by one or more adults, and will play amongst themselves.<ref name=estes/> Like many other large mammals, hippos are described as [[k-selection|K-strategists]], in this case typically producing just one large, well-developed infant every couple of years (rather than many small, poorly developed young several times per year, as is common among small mammals such as rodents).<ref name="Endocrine"/><ref name="Infanticide">{{Cite journal|doi = 10.1080/08927014.1998.9522857|title = Infanticide in the hippopotamus: evidence for polygynous ungulates|author = Lewison, R.|journal = Ethology, Ecology & Evolution|volume = 10|issue = 3|pages = 277–286|year = 1998| bibcode=1998EtEcE..10..277L |url = http://www.fupress.net/index.php/eee/article/viewFile/805/751|access-date = 11 July 2010|archive-date = 6 March 2011|archive-url = https://web.archive.org/web/20110306033554/http://www.fupress.net/index.php/eee/article/viewFile/805/751|url-status = dead}}</ref> Calves no longer need to suckle when they are a year old.<ref name="The Hippos"/>{{rp|64}}

===Interspecies interactions===
[[File:Kruger-Park-Hippo-And-Crocodile.jpg|thumb|right|A hippopotamus and Nile crocodile side by side in Kruger National Park]]
Hippos coexist alongside a variety of large predators in their habitats. [[Nile crocodile]]s, [[lion]]s, and [[spotted hyena]]s are known to prey on young hippos.<ref name=estes/> Beyond these, adult hippos are not usually preyed upon by other animals due to their aggression and size. Cases where large lion prides have successfully preyed on adult hippos have been reported, but it is generally rare.<ref>{{cite book|last = Hunter|first = Luke|title = Carnivores of the World|publisher = [[Princeton University Press]]|year = 2011|isbn = 978-0-691-15228-8}}</ref> Lions occasionally prey on adults at [[Gorongosa National Park]] and calves are sometimes taken at Virunga.<ref>{{Cite book | last= Schaller |first= George B. |year= 1972 |title= The Serengeti lion: A study of predator–prey relations|publisher= University of Chicago Press|pages=208–209|isbn = 978-0-226-73639-6 }}</ref> [[Crocodile]]s are frequent targets of hippo aggression, probably because they often inhabit the same [[riparian]] habitats; crocodiles may be either aggressively displaced or killed by hippos.<ref>{{cite book|last1 = Ross|first1 = Charles A.|last2 = Garnett|first2 = Stephen|title = Crocodiles and Alligators|publisher = Checkmark Books|year = 1989|isbn = 978-0-8160-2174-1}}</ref> Although they will avoid crocodiles larger than {{cvt|3.5|m}}.<ref name="Kofron 1993">{{cite journal |last=Kofron |first=Christopher |title= Behavior of Nile Crocodiles in a Seasonal River in Zimbabwe |journal= American Society of Ichthyologists and Herpetologists |date=May 3, 1993 |volume=1993 |issue=2 |pages=463-469 |jstor= 1447146}}</ref> In turn, very large Nile crocodiles have been observed preying occasionally on calves, "half-grown" hippos, and possibly also adult female hippos. Groups of crocodiles have also been observed finishing off still-living male hippos that were previously injured in mating battles with other males.<ref name="Cott">{{cite journal|author=Cott, H. B. |title=Scientific results of an inquiry into the ecology and economic status of the Nile crocodile (''Crocodilus niloticus'') in Uganda and Northern Rhodesia|journal=The Transactions of the Zoological Society of London|volume=29|issue=4|pages=211–356|doi=10.1111/j.1096-3642.1961.tb00220.x|year=2010}}</ref><ref name="Guggisberg">{{cite book | author = Guggisberg, C. A. W. | title = Crocodiles: Their Natural History, Folklore, and Conservation| year = 1972 | isbn = 978-0-7153-5272-4 | page = 195| publisher = David & Charles}}</ref>

Hippos occasionally visit [[cleaning stations]] in order to be cleaned of parasites by certain species of fishes. They signal their readiness for this service by opening their mouths wide. This is an example of [[Mutualism (biology)|mutualism]], in which the hippo benefits from the cleaning while the fish receive food.<ref>{{cite book|author1 =Balcombe, Jonathan|year=2006|title=Pleasurable Kingdom: Animals and the Nature of Feeling Good|url =https://archive.org/details/pleasurablekingd00balc_653|url-access =limited|publisher=Palgrave Macmillan|pages=[https://archive.org/details/pleasurablekingd00balc_653/page/n140 132]–133|isbn=978-1-4039-8602-3}}</ref> Hippo defecation creates [[allochthonous]] deposits of organic matter along the river beds. These deposits have an unclear ecological function.<ref name="Grey">{{Cite journal|title = Using Stable Isotope Analyses To Identify Allochthonous Inputs to Lake Naivasha Mediated Via the Hippopotamus Gut| author = Grey, J.| author2 = Harper, D. M.|journal = Isotopes in Environmental Health Studies|volume = 38|issue = 4|year = 2002|pages = 245–250|doi = 10.1080/10256010208033269| pmid = 12725427| bibcode = 2002IEHS...38..245G| s2cid = 216152807}}</ref> A 2015 study concluded hippo dung provides nutrients from terrestrial material for fish and aquatic invertebrates,<ref>{{cite journal|author=McCauley, D. J.|year=2015|title=Carbon stable isotopes suggest that hippopotamus-vectored nutrients subsidize aquatic consumers in an East African river|journal=Ecosphere|volume=6|issue=4|pages=1–11|doi=10.1890/ES14-00514.1|display-authors=etal|doi-access=free}}</ref> while a 2018 study found that their dung can be toxic to aquatic life in large quantities, due to absorption of dissolved oxygen in water bodies.<ref>{{cite journal|author1=Dutton, C. L. |author2=Subalusky, A. L. |author3=Hamilton, S. K. |author4=Rosi, E. J. |author5=Post, D. M. |year=2018|title=Organic matter loading by hippopotami causes subsidy overload resulting in downstream hypoxia and fish kills|journal=Nature Communications|volume=9|issue=1951|page=1951 |doi=10.1038/s41467-018-04391-6|pmid=29769538 |pmc=5956076|bibcode=2018NatCo...9.1951D }}</ref><ref>{{cite web |url=https://www.theatlantic.com/science/archive/2018/05/hippos-poop-so-much-that-sometimes-all-the-fish-die/560486/ |title=Hippos Poop So Much That Sometimes All the Fish Die |last=Yong |first=Ed |work=The Atlantic |date=16 May 2018 |access-date=23 June 2021 }}</ref>

The parasitic [[monogenea]]n [[flatworm]]'' Oculotrema hippopotami'' infests hippopotamus eyes, mainly the nictitating membrane. It is the only monogenean species (which normally live on fish) documented to live on a mammal.<ref>{{cite journal|author1=Rubtsova, N. Y.|author2=Heckmann, R. A.|author3=Smit, W. J.|author4=Luus-Powell, W. J.|author5=Halajian, A.|author6=Roux, F.|year=2018|title=Morphological studies of developmental stages of ''Oculotrema hippopotami'' (Monogenea: Polystomatidae) infecting the eye of ''Hippopotamus amphibius'' (Mammalia: Hippopotamidae) ssing SEM and EDXA with notes on histopathology|journal=The Korean Journal of Parasitology|volume=56|issue=5|pages=463–475|doi=10.3347/kjp.2018.56.5.463|pmid=30419732 |pmc=6243182 |s2cid=53289954 }}</ref>