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

• Approximately 35 days

Birth

• 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

Juvenile/Subadult

• 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

Adult

• 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

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

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

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)