Skip to Main Content
It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
San Diego Zoo Wildlife Alliance logo
San Diego Zoo Wildlife Alliance Library logo

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

Gestation: 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


(Martin et al. 2008)

Up to 18 years in wild recorded
Wild average around 12 years

  • 14+ years under ideal conditions
  • Much shorter near human habitation


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)

SDZWA Library Links