Editing Pinniped (section)

===Birth and parenting===
[[File:Harbor seal is nurcing at Point Lobos.jpg|thumb|left|Harbor seal mother nursing pup]]
Except for the walrus, which has five- to six-year gaps between births, female pinnipeds enter [[estrous|estrus]] shortly after they give birth, and can thus produce pups every year. All species have [[delayed implantation]], in which the [[embryo]] does not enter the [[uterus]] for weeks or months.{{sfn|Berta|2012|pp=75–76}} Delayed implantation allows the female to wait until conditions are right for birthing.{{sfn|Berta|2012|p=76}}{{sfn|Riedman|1990|p=224}} [[Gestation]] in seals (including delayed implantation) typically lasts a year.{{sfn|Berta|2012|pp=76–78}} For most species, birthing takes place in spring and summer.{{sfn|Riedman|1990|p=245}} Usually, single pups are born;{{sfn|Berta|2012|pp=76–78}} twins are rare and have high mortality rates.{{sfn|Riedman|1990|p=222}} Pups of most species are born relatively developed and [[precocial]].{{sfn|Berta|2012|pp=76–78}}

Pinniped milk has "little to no [[lactose]]".{{sfn|Riedman|1990|p=265}} Mother pinnipeds have different strategies for maternal care and lactation. Phocids such as elephant seals, grey seals and hooded seals have a lactation period that lasts days or weeks, during which they fast and nurse their pups on land or ice. The milk of these species consists of up to 60% [[fat]], allowing the young to grow quickly. Each day until they are weaned, northern elephant seal pups gain {{convert|4|kg|0|abbr=on}}. Some pups gain weight more quickly than others by stealing extra milk from other mothers. [[Alloparenting]] occurs in these fasting species;{{sfn|Berta|2012|pp=76–77}} while most northern elephant seal mothers nurse their own pups and reject nursings from alien pups, some do accept alien pups with their own.<ref>{{cite journal|author1=Riedman, M. L. |author2=Le Boeuf, B. J. |year=1982 |title=Mother-pup separation and adoption in northern elephant seals |journal=Behavioral Ecology and Sociobiology |volume=11 |issue=3 |pages=203–13 |jstor=4599535|doi=10.1007/BF00300063|s2cid=2332005 }}</ref>
[[File:Fur seals at south georgia.jpg|thumb|right|Adult [[Antarctic fur seal]] with pups]]
For otariids and some phocids like the harbor seal, mothers fast and nurse their pups for a few days at a time. In between nursing bouts, the females forage at sea while the young stay behind onshore. If there is enough food close to shore, a female can be gone for as little as a day, but otherwise may be at sea for as long as three weeks.{{sfn|Berta|2012|pp=77–78}} Lactation in otariids may last 6–11 months; in the [[Galápagos fur seal]] it can last up to three years. Pups of these species are weaned at heavier weights than their phocid counterparts, but the latter grow quicker.<ref>Mann, J. "Parental behavior" in {{harvnb|Perrin|Würsig|Thewissen|2009|pp=830–835}}</ref> Walruses are unique in that mothers nurse their young at sea.{{sfn|Berta|2012|p=78}} Young pinnipeds typically start swimming on their own and some species can even swim as newborns. Young may wait days or weeks before entering the water; elephant seals start swimming weeks after weaning.<ref>{{cite book |author=Renouf, D. |year=2012 |title=The Behaviour of Pinnipeds |publisher=Springer Science & Business Media |page=263 |isbn=9789401131001}}</ref>

Male pinnipeds generally play little role in raising the young.<ref name="Cassini"/> Male walruses may help inexperienced young as they learn to swim, and have even been recorded caring for orphans. When a group is threatened, all the adults may protect the young.{{sfn|Riedman|1990|p=290}} Male California sea lions have been observed to help shield swimming pups from predators.<ref name="Walker 2003">{{cite book |author=Nowak, R. M. |year=2003 |title=Walker's Marine Mammals of the World |publisher=[[Johns Hopkins University Press]] |pages=80–83 |isbn=978-0-8018-7343-0}}</ref> Males can also pose threats to the safety of pups, particularly during fights.<ref name="Cassini">{{cite journal|author=Cassini, M. H. |year=1999 |title=The evolution of reproductive systems in pinnipeds |journal=Behavioral Ecology |volume=10 |issue=5 |pages=612–616 |doi=10.1093/beheco/10.5.612|doi-access=free }}</ref> Pups of some species may be abducted, assaulted and [[Infanticide (zoology)|killed]] by males, possibly due to sexual frustration.<ref>{{cite journal |author1=Campagna, C. |author2=Le Boeuf, B. J. |author3=Cappozzo, J. H. |year=1988 |title=Pup abduction and infanticide in southern sea lions |journal=Behaviour |volume=107|issue=1–2 |pages=44–60 |jstor=4534718 |doi=10.1163/156853988X00188}}</ref>