Editing Koala (section)

===Reproduction and development===
[[File:Koala Foetus Almost At Birth.jpg|thumb|right|upright|A young joey, preserved at Port Macquarie Koala Hospital]]
Koalas are seasonal breeders, and they give birth from October to May. Females in [[oestrus]] lean their heads back and shake their bodies. Despite these obvious signals, males try to copulate with any female during this period, mounting them from behind. Because of his much larger size, a male can overpower a female. A female may scream and vigorously fight off her suitors but will accede to one that is dominant or familiar. The commotion can attract other males to the scene, obliging the incumbent to delay mating and fight off the intruders. A female may learn who is more dominant during these fights.<ref name="Martin-Handasyde"/>{{rp|58–60}} Older males typically accumulate scratches, scars, and cuts on the exposed parts of their noses and their eyelids.<ref name=moyal/>{{rp|192}}

Koalas are [[Induced ovulation (animals)|induced ovulator]]s.<ref name="Johnston 629–634">{{Cite journal|last1=Johnston|first1=S. D.|last2=O'Callaghan|first2=P.|last3=Nilsson|first3=K.|last4=Tzipori|first4=G.|last5=Curlewis|first5=J. D.|date=1 November 2004|title=Semen-induced luteal phase and identification of a LH surge in the koala (''Phascolarctos cinereus'')|journal=Reproduction|language=en|volume=128|issue=5|pages=629–634|doi=10.1530/rep.1.00300|issn=1470-1626|pmid=15509709|doi-access=free}}</ref> The gestation period lasts 33–35 days,<ref>{{cite journal |author1=Gifford, A. |author2=Fry, G. |author3=Houlden, B. A. |author4=Fletcher, T. P. |author5=Deane, E. M. |title=Gestational length in the koala, ''Phascolarctos cinereus'' |journal=Animal Reproduction Science |year=2002 |volume=70 |issue=3 |pages=261–66 |doi=10.1016/S0378-4320(02)00010-6 |pmid=11943495}}</ref> and a female gives birth to one [[Joey (marsupial)|joey]] or occasionally, twins. The young are born tiny and barely formed, weighing no more than {{cvt|0.5|g}}. However, their lips, forelimbs, and shoulders are relatively advanced, and they can breathe, defecate, and urinate. The joey crawls into its mother's pouch to continue its development.<ref name="Martin-Handasyde"/>{{rp|61}} Female koalas do not clean their pouches, while an unusual trait among marsupials.<ref name=moyal/>{{rp|181}}

The joey latches on to one of the female's two teats and suckles it.<ref name="Martin-Handasyde"/>{{rp|61}} The female lactates for as long as a year to make up for her low energy production. Unlike in other marsupials, koala milk becomes less fatty as the joey grows.<ref name="Martin-Handasyde"/>{{rp|62}} After seven weeks, the joey has a proportionally large head, clear edges around its face, more colouration, and a visible pouch (if female) or scrotum (male). At 13 weeks, the joey weighs around {{cvt|50|g}}, and its head doubles in size. The eyes begin to open and hair begins to appear. At 26 weeks, the fully furred animal resembles an adult and can look outside the pouch.<ref name="Martin-Handasyde"/>{{rp|63}}
[[File:Koala and joey.jpg|thumb|left|Mother with joey on back]]
At six or seven months, the joey weighs {{cvt|300|-|500|g}} and fully emerges from the pouch for the first time. It explores its new surroundings cautiously, clutching its mother for support.<ref name="Martin-Handasyde"/>{{rp|65}} Around this time, the mother prepares it for a eucalyptus diet by producing a faecal pap that the joey eats from her cloaca. This pap comes from the cecum, is more liquid than regular faeces, and is filled with bacteria.<ref>{{cite journal|last1=Osawa|first1=R|last2=Blanshard|first2=W. H.|last3=O'Callaghan|first3=P. G.|year=1993|title=Microbiological studies of the intestinal microflora of the koala, ''Phascolarctos-Cinereus'' .2. pap, a special maternal feces consumed by juvenile koalas|journal=Australian Journal of Zoology|volume=41|issue=6|pages=611–620|doi=10.1071/ZO9930611}}</ref> A nine month old joey has its adult coat colour and weighs {{cvt|1|kg}}. Having permanently left the pouch, it rides on its mother's back for transportation, learning to climb by grasping branches.<ref name="Martin-Handasyde"/>{{rp|65–66}} Gradually, it becomes more independent. The mother becomes pregnant again after a year after the offspring reaches around {{cvt|2.5|kg}}. She permanently severs her bond with her previous offspring and no longer allows it to suckle, but it remains nearby until it is one-and-a-half to two years old.<ref name="Martin-Handasyde"/>{{rp|66–67}}

Females become sexually mature at about three years of age; in comparison, males reach sexual maturity at about age four<ref>{{cite journal |author=Ellis, W. A. H. |author2=Bercovitch, F. B. |title=Body size and sexual selection in the koala |journal=Behavioral Ecology and Sociobiology |year=2011 |volume=65 |issue=6 |pages=1229–35 |doi=10.1007/s00265-010-1136-4|bibcode=2011BEcoS..65.1229E |s2cid=26046352 }}</ref> although they can experience [[spermatogenesis]] as early as two years.<ref name="Martin-Handasyde"/>{{rp|68}} Males do not start marking their scent until they reach sexual maturity though their chest glands become functional much earlier.<ref name="Tobey 2009"/> Koalas can breed every year if environmental conditions are good, though the long dependence of the young usually leads to year-long gaps in births.<ref name="Tyndale-Biscoe"/>{{rp|236}}