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Koala (Phascolarctos cinereus) Fact Sheet: Reproduction & Development


Male shows no obvious courtship behavior, other than bellowing and scent marking trees (Bercovitch et al. 2006)
If male approaches, female tries to back away and makes defensive vocalizations

  • In response, males may abandon female's tree, or may attempt to mate


Structure of koala mating system is unclear to researchers using radio-collared koalas (Ellis & Bercovitch 2011):

  • Female mate choice may be the "key mediator of male reproductive output"

Females are induced ovulators, unlike most other marsupials

  • Egg released during or after copulation

Breeding: October - November (spring) in southern hemisphere
Inter-birth interval: once every 1 - 2 years
Females are seasonally polyestrous (repeated estrus cycles during the breeding season) (Johnston et al 2000a)
In a study of a female koala in managed care, a pre-estrus state may be predicted from (Takahashi et al 2009)

  • Increased bellowing
  • Increased activity
  • Weight loss

Reproductive life-history of koalas similar to placental mammals (Tobey et al. 2006)

  • Slow infant growth rates
  • Prolonged carrying of dependent young
  • Long intervals between births

Gestation & Birth


  • Approximately 35 days

Life Stages


  • Birthing season: (Ellis et al. 2010a)
    • Young can be born every month of the year across Australia
    • Most often from December through March (fall-winter)
    • A great deal of variability between northern and southern Australia populations
    • In a population at San Diego Zoo most joeys are born in spring-summer
  • Litter size: one, rarely two
  • Birth weight: less than 0.5 g (.02 oz)
  • Size: about 2 cm (.8 in) long
  • Sex and locality differences in timing of births:
    • In southern Australia, half of males born in November; half of females not born until end of December (McLean & Handasyde 2006)
    • In northern Australia (Queensland) no differences in timing (Ellis et al. 2010a)
  • Sex ratios at birth:
    • More males produced at birth than females in some southern Australian populations (Ellis et al.2010a)
    • Reasons for this bias not understood
  • As with all marsupials, newborn is blind, very underdeveloped, and fetal-like
  • At birth, koala arms and claws more developed than a newborn placental mammal's
    • Marsupials need to haul themselves (unaided) through mother's fur to reach the pouch
  • Senses of touch and smell well developed

Infant (< 1 year old)

  • Young called "joey"
  • Develops in pouch for 6 months, and then starts making short excursions outside of pouch
  • Once outside of pouch, young rides on mother's back
  • Starts feeding on pap (Martin & Handasyde 1999)
    • Mother excrets this paste of partially digested leaves which she produces in the caecum of the intestines
    • Pap contains microorganisms the young needs to digest Eucalyptus leaves
  • Continues drinking milk for up to year
    • Mother's milk at time of joey's pouch exit has become low-fat with few other solids (Krockenberger 1996)
    • Mother's milk composition may be an adaptation for their Eucalyptus diet that is nutrition-poor (Krockenberger 1996)
    • Nursing lasts 55% longer in these marsupials than would be predicted from their body weight (Russell 1982
  • Females will occasionally care for an unrelated joey


  • Leaves pouch at 7-8 months
  • Independent of mother: 12-24 months of age, when next joey is born
  • Remains close by for several more months
  • Males tend to leave natal home range
  • Females tend to set up home range nearby


  • Sexual maturity:
    • Females sexually mature at approximately 6 kg (13 lbs), at 2 - 3 years
    • Males sexually mature at 2 years, but mating success is low until 4th or 5th year
  • Sternal gland
    • Begins to develop in males at about 1.5 - 3 years of age

Typical Life Expectancy

Wild populations

  • About 10–12 years, on average (Queensland Government 2023); Martin et al. (2008) state 10–14 years
    • Females tend to live slightly longer than males

Managed care

  • Queensland koala (Phascolarctos cinereus adustus)
    • Median life expectancy
      • 10.1 years (AZA 2023)


Main causes of mortality

  • Disease
  • Being hit by cars
  • Predation by dogs/dingoes (vulnerable when on ground)
  • Natural predators include goanna lizards and a very large owl with a 140 cm (55 in) wingspan, (Ninox strenus)
  • Drought: reduces availability of forage, causing death due to starvation or poor nutrition
  • Fire
  • See Threats to Survival for more information

Joey Holds onto Mother

mom and baby koala

Young koalas stay in the pouch for up to 8 months.

After exiting, they travel on their mother’s back and continue nursing for another 4 months. They will stay with the mother until the next joey is born, sometimes not until two years of age.

Image credit: © sillypucci from Flickr. Some rights reserved

Page Citations

Bercovitch et al. (2006)
Ellis et al. (2009)
Ellis et al. (2010a)
Ellis & Bercovitch (2011)
Gordon et al. (1990)
Johnston et al. (2000)
Krockenberger (1996)
Lee & Martin (1988)
Martin (2001)
Martin et al. (2008)
Martin & Handasyde (1990, 1999)
McLean & Handasyde (2006)
Mitchell (1990a)
Russell (1982)
Smith (1980a,b,c)
Takahashi et al. (2009)
Thompson (1987)
Tobey et al. (2006)
White & Kunst (1990)

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