Editing Hippopotamus (section)

===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>