Editing Hippopotamus (section)

===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}}