Editing Cetacea (section)

== Life history ==

=== Reproduction and brooding ===
Most cetaceans sexually mature at seven to 10 years. An exception to this is the [[La Plata dolphin]], which is sexually mature at two years, but lives only to about 20. The sperm whale reaches sexual maturity within about 20 years and has a lifespan between 50 and 100 years.<ref name="mann" />

For most species, reproduction is seasonal. [[Ovulation]] coincides with male [[fertility]]. This cycle is usually coupled with seasonal movements that can be observed in many species. Most toothed whales have no fixed bonds. In many species, females choose several partners during a season. Baleen whales are largely [[Monogamy in animals|monogamous]] within each reproductive period.{{citation needed|date=October 2024}}

Gestation ranges from 9 to 16 months. Duration is not necessarily a function of size. Porpoises and blue whales gestate for about 11 months. As with all mammals other than marsupials and monotremes, the embryo is fed by the [[placenta]], an organ that draws nutrients from the mother's bloodstream. Mammals without placentas either lay minuscule eggs (monotremes) or bear minuscule offspring (marsupials).{{citation needed|date=October 2024}}

Cetaceans usually bear one calf. In the case of twins, one usually dies, because the mother cannot produce sufficient milk for both. In modern cetaceans, the fetus is usually positioned for a tail-first delivery. Contrary to popular belief, this is not to minimize the risk of drowning during delivery. More likely it has to do with the mechanics of birthing and the shape of the fetus.<ref>{{Cite journal |last1=Miedema |first1=Feiko |last2=Klein |first2=Nicole |last3=Blackburn |first3=Daniel G. |last4=Sander |first4=P. Martin |last5=Maxwell |first5=Erin E. |last6=Griebeler |first6=Eva M. |last7=Scheyer |first7=Torsten M. |date=2023-04-18 |title=Heads or tails first? Evolution of fetal orientation in ichthyosaurs, with a scrutiny of the prevailing hypothesis |journal=BMC Ecology and Evolution |volume=23 |issue=1 |pages=12 |doi=10.1186/s12862-023-02110-4 |doi-access=free |issn=2730-7182 |pmc=10114408 |pmid=37072698}}</ref> After birth, the mother carries the infant to the surface for its first breath. At birth, they are about one-third of their adult length and tend to be independently active, comparable to terrestrial [[mammals]].{{citation needed|date=October 2024}}

==== Suckling ====
Like other placental mammals, cetaceans give birth to well-developed calves and nurse them with milk from their [[mammary glands]]. When suckling, the mother actively splashes milk into the mouth of the calf, using the muscles of her mammary glands, as the calf has no lips. This milk usually has a high-fat content, ranging from 16 to 46%, causing the calf to increase rapidly in size and weight.<ref name="mann" />

In many small cetaceans, suckling lasts for about four months. In large species, it lasts for over a year and involves a strong bond between mother and offspring.{{citation needed|date=October 2024}}

In several species of both whales and dolphins, [[alloparenting]] has been observed.<ref>{{Cite journal |last1=Konrad |first1=Christine M |last2=Frasier |first2=Timothy R |last3=Whitehead |first3=Hal |last4=Gero |first4=Shane |date=2019-03-04 |title=Kin selection and allocare in sperm whales |url=https://academic.oup.com/beheco/article-abstract/30/1/194/5144394?redirectedFrom=fulltext |journal=Behavioral Ecology |volume=30 |issue=1 |pages=194–201 |doi=10.1093/beheco/ary143 |issn=1045-2249}}</ref><ref>{{Cite news |last=Weston |first=Phoebe |date=2023-03-10 |title='Extraordinary' sighting of orca with baby pilot whale astounds scientists |url=https://www.theguardian.com/environment/2023/mar/10/killer-whale-orca-adopts-abducts-pilot-whale-calf-aoe |access-date=2025-02-09 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref>

This reproductive strategy provides a few offspring that have a high survival rate.{{citation needed|date=October 2024}}

=== Lifespan ===
Among cetaceans, whales are distinguished by an unusual longevity compared to other higher mammals. Some species, such as the [[bowhead whale]] (''Balaena mysticetus''), can reach over 200 years. Based on the annual rings of the bony [[otic capsule]], the age of the oldest known specimen is a male determined to be 211 years at the time of death.<ref>{{cite journal|author1=John C George|author2=Jeffrey Bada|author3=Judith Zeh|author3-link= Judy Zeh |author4=Laura Scott|author5=Stephen E Brown|author6=Todd O'Hara|author7=Robert Suydam|title=Age and growth estimates of bowhead whales (''Balaena mysticetus'') via aspartic acid racemization|journal=Canadian Journal of Zoology|year=1999|volume=77|issue=4|doi=10.1139/z99-015|pages=571–580|bibcode=1999CaJZ...77..571G }}<!--|access-date=5 September 2015--></ref>

=== Death ===
{{Main|Whale fall}}
Upon death, whale carcasses fall to the deep ocean and provide a substantial habitat for marine life. Evidence of whale falls in present-day and fossil records shows that deep-sea whale falls support a rich assemblage of creatures, with a global diversity of 407 species, comparable to other [[neritic]] biodiversity hotspots, such as [[cold seep]]s and [[hydrothermal vent]]s.<ref name="Smith&Baco2003">{{cite book |url=http://www.soest.hawaii.edu/oceanography/faculty/csmith/Files/Smith%20and%20Baco%202003.pdf |archive-url=https://web.archive.org/web/20060817174541/http://www.soest.hawaii.edu/oceanography/faculty/csmith/Files/Smith%20and%20Baco%202003.pdf |archive-date=2006-08-17 |url-status=live |title=Ecology of Whale Falls at the Deep-Sea Floor |author1=Smith, Craig R. |author2=Baco, Amy R. |volume=41 |date=2003 |pages=311–354 |access-date=23 August 2014 |doi=10.1201/9780203180594.ch6|series=Oceanography and Marine Biology - an Annual Review |doi-broken-date=2024-11-11 |isbn=978-0-415-25462-5 }}</ref>

Deterioration of whale carcasses happens through three stages. Initially, organisms such as [[shark]]s and [[hagfish]] scavenge the soft tissues at a rapid rate over a period of months and as long as two years. This is followed by the colonization of bones and surrounding sediments (which contain organic matter) by enrichment opportunists, such as [[crustaceans]] and [[polychaetes]], throughout a period of years. Finally, sulfophilic bacteria reduce the bones releasing [[hydrogen sulfide]] enabling the growth of [[chemoautotrophic]] organisms, which in turn, support organisms such as mussels, clams, limpets and sea snails. This stage may last for decades and supports a rich assemblage of species, averaging 185 per site.<ref name="Smith&Baco2003" /><ref>{{cite journal |author1=Fujiwara, Yoshihiro|title=Three-year investigations into sperm whale-fall ecosystems in Japan |journal=Marine Ecology |volume=28 |issue=1 |pages=219–230|date=16 February 2007|display-authors=etal |doi=10.1111/j.1439-0485.2007.00150.x|bibcode=2007MarEc..28..219F|doi-access=free}}</ref>