Editing Steller sea lion (section)

=== Reproduction ===
[[File:2008 Juneau Steller Sea Lion Haram (8101629225).jpg|thumb|Adult bull, females, and pups near [[Juneau, Alaska]], US]]

Reproductively mature male sea lions gather together mid-spring on traditional, well-defined reproductive [[rookery|rookeries]], usually on beaches on isolated islands. The larger, older males establish and defend distinct territories on the rookery. A week or so later, adult females arrive, accompanied occasionally by sexually immature offspring, and form fluid aggregations throughout the rookery. Like all other [[Otariidae|otariids]], Steller sea lions are [[Polygyny in animals|polygynous]]. However, unlike some other species, they do not coerce individual females into harems, but control spatial territories among which females freely move. Steller sea lions have used aquatic, semiaquatic, and terrestrial territories. Males with semiaquatic territories have the most success in defending them. The boundaries are defined by natural features, such as rocks, faults, or ridges in rocks, and territories can remain stable for&nbsp;60 days.<ref name="Gentry 1970">Gentry, R. L. (1970). "Social Behavior of the Steller’s Sea Lion". PhD Thesis, University of California, Santa Cruz, CA.</ref><ref name= 'Sandergen 1970'>Sandergen, F. E. (1970). 'Breeding and Maternal Behavior of the Steller's Sea Lion (''Eumetopias jubatus'') in Alaska', M. S. Thesis, University of Alaska, College.</ref> Though Steller sea lion males are generally tolerant of pups, one male filmed on [[Medny Island]] in Russia was documented killing and eating several pups in a first-ever recorded incident of [[cannibalism]]. Though researchers are uncertain as to the motives or reasons behind said attacks, it is suggested that the bull involved may have an abnormal personality akin to being psychotic.<ref>{{cite web|url=http://news.nationalgeographic.com/2017/08/sea-lions-cannibalism-russia-killing/|archive-url=https://web.archive.org/web/20170816075755/http://news.nationalgeographic.com/2017/08/sea-lions-cannibalism-russia-killing/|url-status=dead|archive-date=16 August 2017|title=Cannibal Sea Lion Kills and Eats Pup—Never Before Seen|date=16 August 2017|website=nationalgeographic.com}}</ref>

Pregnant females give birth soon after arriving on a rookery, and copulation generally occurs one to two weeks after giving birth,<ref name="Gentry 1970"/><ref name="Sandergen 1970"/> but the fertilized egg does not become implanted in the uterus until the fall. A fertilized egg may remain in [[embryonic diapause]] for up to three months before implanting and beginning to divide.<ref name=":0">{{Cite journal|last=Pitcher|first=Kenneth W.|date=1998|title=Reproductive Performance of female Steller sea lions: an energetics-based reproductive strategy?|journal=Canadian Journal of Zoology|volume=76|issue=11|pages=2075–2083|doi=10.1139/z98-149|bibcode=1998CaJZ...76.2075P }}</ref> Twins are rare.<ref>[https://www.adfg.alaska.gov/index.cfm?adfg=stellersealion.main Alaska Department of Fish and Game, "Life History"]. Adfg.alaska.gov. Retrieved on 17 December 2011.</ref> After a week or so of nursing without leaving the rookery, females begin to take progressively longer and more frequent foraging trips leaving their pups behind until at some point in late summer, when both the mother and pup leave the rookery together. This maternal attendance pattern is common in otariids. As pups get older the amount of time spent by females foraging out at sea increases. This continues until pups obtain the ideal body weight and energy reserves to eat on their own. A study conducted by the University of California, Santa Cruz found that on average male pups consume more milk than females. This may be due to the sexual dimorphism common to otariids.<ref>{{Cite journal|last=Higgins|first=Lesley V.|date=January 1988|title=Behavioral and Physiological Measurements of Maternal Investment in the Steller Sea Lion, Eumetopias jubatus|journal=Marine Mammal Science|volume=4|issue=1 |pages=44–58|doi=10.1111/j.1748-7692.1988.tb00181.x|bibcode=1988MMamS...4...44H }}</ref> Reproductive males fast throughout the reproductive season,<ref>Riedman, M. (1990). [https://archive.org/details/pinnipedssealsse0000ried/page/200 ''The Pinnipeds: Seals, Sea lions, and Walruses.''] Los Angeles, University of California Press. p. 200 {{ISBN|0-520-06497-6}}.</ref> often without entering the water once from mid-May until August, when the structure of the reproductive rookeries begins to fall apart and most animals leave for the open seas and disperse throughout their range.
[[Image:wikipup.jpg|thumb|Steller sea lion pup on Antsiferov Island in the Kuril Islands, Russia]]
The age at weaning is highly variable; pups may remain with their mothers for as long as four years. Incidents of mothers feeding daughters that are simultaneously feeding their own newborn pups have been documented, which is an extremely rare occurrence among mammals. A study done at Año Nuevo in 1983 found that female attendance and time spent with their pup was shaped by increasing nutritional demands of the pup and the pups suckling efficiency. Females averaged 21 hours ashore and 36 hours at sea. As the pups aged, females began to spend more time at sea again. As the pups matured, specifically at the sixth week past birth, the mother's sea time declined by 30 percent. There was no relationship between the pups' activity or physical excursion and their suckling time, age, or sex. Their suckling time, and age, and sex are unrelated to their use of energy. Labeled water studies showed that the pups' milk intake had a direct relationship to their size. Pups that consumed more milk were heavier than those that did not. These findings show that the amount of time females spend onshore with their pups is based on their pup's suckling efficiency and nutritional demands.<ref>{{Cite journal|last1=Higgins|first1=Lesley V.|last2=Costa|first2=Daniel P.|last3=Huntley|first3=Anthony C.|last4=Boeuf|first4=Burney J.|date=January 1988|journal=Marine Mammal Science|volume=4|issue=1|pages=44–58|doi=10.1111/j.1748-7692.1988.tb00181.x|issn=0824-0469|title=Behavioral and Physiological Measurements of Maternal Investment in the Steller Sea Lion, Eumetopias Jubatus|bibcode=1988MMamS...4...44H }}</ref>

In the past, the low pup production has been tied to an increase in nutritional stress found in females. This was believed to have contributed to the decline in Steller sea lions common to Alaska.<ref name=":0" />