Red Kangaroo (Macropus rufus) Fact Sheet: Reproduction & Development

• Opportunistic breeders; can produce an independent young every 240 days when vegetation is lush (Newsome 1964; Lee & Cockburn 1985)
• Reproductive style adapted to environmental uncertainty
• Females can stop reproduction when faced with conditions unfavorable for survival of young
• Breeding can occur year-round, but only given good conditions
• Drought-breaking rain stimulates female ovulation, often within 14 days of rain (Newsome 1964)
• Young can be successfully suckled 3-4 months during a drought
• Fertility during droughts
• Early in drought periods, fertility is maintained (Newsome 1997)
• Late in drought many males and females become infertile (Newsome 1997)
• In modern landscapes, infertility may be a result of heat stress from occupying treeless habitats (no shade) created by cattle ranching
• An unusual feature of kangaroo reproduction: embryonic diapause (Dawson 1995):
• Viable embryo (of only 70-100 cells - a blastocyst) can be carried in uterus for many months
• Embryo will develop further only if female does not have a nursing joey or the joey is tapering off its milk demands
• Young from blastocyst stage will have developed to birth stage within a day of the previous young's exit from the pouch

• Very short gestation compared to placental mammals
  • 33 days (Grzimek & Ganslosser 1990) which is longer than in other marsupials (Dawson 1995)
  • Within marsupials, this gestation lasts longer and confers advantage having young born more developed
• After birth, 235 days spent in pouch (Grzimek & Ganslosser 1990)

Birth

• At birth, marsupial mammals are much smaller compared to their mother's size than any placental mammal (Janssens et al. 1997):
  • Smallest placental mammal at birth: a giant panda is one thousandth the mother's weight
  • Marsupial mammal at birth: one ten-thousandth to one hundred-thousandth the mother's weight
• One kangaroo born per pregnancy (Grzimek & Ganslosser 1990)
  • Two occasionally reported (Wilson & Mittermeier 2015)
• Weight at birth: 1 g (0.03 oz) (Grzimek & Ganslosser 1990)
• Newborn travels up mother's belly and fastens to a teat in about 3 minutes

Young of the year (< 1 year old)

• For 70 days in the pouch, joey is attached to a teat
• Mother consumes feces and urine of joey, thus recycling 1/3 of water used to produce milk (Staker 2006)
• By 190 days and 2 kg (4.4 lb) weight, young is furred and can exit pouch for short periods (Munn et al. 2007)
  • A joey that hasn't yet exited the pouch has soft pink soles; after hopping on the ground, feet become darker, tougher (Staker 2006)
  • Mother occasionally cleans and grooms pouch; joey must wait outside (Staker 2006)
  • Young joeys outside the pouch may comfort themselves by standing with their head in the pouch; they don't suckle at such times (Dawson 1995)
  • Mother must cooperate by bending down for joey to be able to return to pouch (Dawson 1995)

Juvenile

• Continue to nurse by sticking head back into pouch until about one year and 10-11 kg (22-24 lb) (Munn et al. 2007)
  • Will only use same teat as the original one used when still in the pouch (Munn et al. 2007)
  • Milk of each teat is appropriate for developmental stage of joey (Staker 2006):
    • One teat serves the pouch joey
    • Another teat can feed the older joey outside (Staker 2006)
• Juveniles quite vulnerable to drought (Munn & Dawson 2003):
  • In order to thrive and grow, require 95% of daily energy intake of typical adult female, even though they're only half the size of the female
• A female whose joey dies may call for it for days afterwards (Staker 2006)
•      

Adult

•  Sexual maturity in managed care (Sharman & Calaby 1964)
  • Female: 15-20 months
  • Male: over 2 years
• Sexual maturity in wild (Frith & Sharman 1964; Wilson & Mittermeier 2015)
  • Females: from 15 months; most individuals around 30 months
  • Males: from 24 months; 28-39 months or later in arid regions

Wild populations

• Not well known
• High mortality before age 3 (Frith and Calaby 1969)
• Bilton and Croft (2004) found an average age of 10.8 years in a sample of 12 female red kangaroos

Managed care

• Median life expectancy (AZA 2023)
  • Males: 7.9 years
  • Females: 9.8 years

• Drought affects juveniles more than any other age group (Dawson 1995; Munn & Dawson 2003)
  • In drought periods, up to 83% of young died before weaning
  • In very severe droughts, almost no young survive
• Dingos prey primarily on juvenile kangaroos or smaller adult females (Shepherd 1981)
  • Also see Predators
  • In one 7-week study, 5 dingos killed 83 red kangaroos, 80 of which were juveniles
  • Other studies by Newsome et al. (1973) and Whitehouse (1977) suggest red kangaroos were a major part of dingo diets
  • Kill rates by dingos of red kangaroos have potential to limit rate of increase of kangaroo's population by direct predation
  • May not eat all of each red kangaroo they kill; reasons for overkill unknown
  • Kangaroos develop knowledge of dingos' intent, much as do prey species of the African lions (Shepherd 1981)
    • Large male red kangaroos appear indifferent to the dingo's presence
    • All kangaroos seem to know when dingos aren't actively hunting and pay little attention to them at such times
• Human hunters select larger individuals, especially males and largest females
  • Most hunting employed in controlled harvests and various management strategies
  • Long-term effects of kangaroo harvesting difficult to determine
  • In a study of red kangaroo populations, using two methods for calculating harvest quotas (McCarthy 1996):
    • Quotas should be based on actual environmental conditions of the current and past season
    • When quotas are based on fixed percentages of a population red kangaroos may be at high risk of population declines

Juvenile red kangaroos require 95% of daily energy intake of typical adult female, even though they're only half the female's size.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Dawson (1995)
Frith & Sharman (1964)
Grzimek & Ganslosser (1990)
Janssens et al. (1997)
Lee & Cockburn (1985)
McCarthy (1996)
Munn & Dawson (2003)
Newsome (1964, 1997)
Nowak (1999)
Sharman & Calaby (1964)
Shepherd (1981)