Western Gray Kangaroo (Macropus fuliginosus) Fact Sheet: Reproduction & Development

Intense competition for access to females (Eldridge and Coulson 2015)

• Males guard females from rival males before and after mating
• Males engage in repetitive, ritualized bouts of grooming, display, and sparring/fighting (Eldridge and Coulson 2015)
• In eastern gray kangaroos, dominant males do not hold tenure longer than about a year (Dawson 2013)
• Dominant males at risk of death if seasonal conditions deteriorate (maintaining status is energetically costly and he spends less time feeding)

Assessment of female reproductive state

• Males smell urine of females and exhibit flehmen (lip-curl response) (Eldridge and Coulson 2015)

Mating system

• Males mate with many females (polygynous mating system) (Dawson 2013)
• Sex ratio of adults skewed towards females (Norbury et al. 1988; Neaves et al. 2013)
• Male/female form a pair bond for a short period before copulation; pair bond dissolves quickly after copulation, and male seeks another female in estrus (referred to as “tending bonds”) (McCullough and McCullough 2000)
• Long copulation bouts; reported to be about 50 minutes
• Dominant males are usually the first to mate, but other males may also mate if females are not well-guarded (Dawson 2013)

General

• Reproductive behavior of kangaroos is often studied in managed care, but less studied in the wild (Dawson 2013)
• Like other marsupials, significant development of embryo young occurs outside the uterus in the mother’s pouch (Dawson 2013)
  • For background on marsupial reproductive evolution and anatomy, see Dawson (2013, Chapter 5)
• Mother’s pouch lining is coated with a brown, tacky substance that prevents bacterial and fungal growth (Staker 2006)

Breeding

• Females reach sexual maturity starting at 14 months in the wild, but breeding rarely occurs before 2 years old (16 kg/35 lb) (Dawson 2013; Eldridge and Coulson 2015)
  • Females in managed care mature at 14-18 months
• Can breed throughout the year, but much breeding is seasonal; females usually have one young per year (Poole 1975; Arnold et al. 1991; Dawson 2013; Eldridge and Coulson 2015)
  • Timing of breeding varies and may be influenced by location or genetics (see Discussion of Mayberry et al. 2010)
• Do not exhibit embryonic diapause, as is exhibited by many macropods (embryonic diapause: embryo development is "paused" un utero until pouch young leaves permanently) (Fenelon et al. 2014)
• Female may nurse two young at a time (one tiny joey from the current year and a fully developed joey from the previous year)
  • Also see Milk Nutrition
• Estrous cycle: 35 days, on average (range: 27-54) (Eldridge and Coulson 2015)
  • Female returns to estrus when her joey is about to become independent of her pouch
• Interbreeding in the wild with eastern gray kangaroos (Macropus giganteus) is relatively rare (Coulson and Coulson 2001; Neaves et al. 2010; Dawson 2013; Neaves et al. 2013)
  • Low levels of hybridization when wild population densities drop dramatically due to changes in environmental conditions
  • Interbreed in managed care (Poole 1975)
• Number of male and female young born in managed care reported as being similar (sex ratio 1:1) (Poole 1975)

Pregnancy

• Gestation period: 31 days, on average (range: 27-54) (Eldridge and Coulson 2015)
• Females give birth to one young (Eldridge and Coulson 2015)
  • Twins occasionally reported (Eldridge and Coulson 2015), but only one survives (Sarah Garnick, personal communication, 2017)
• Females much more likely to breed successfully after droughts end; as few as 20% carry young during drought (Eldridge and Coulson 2015; also see Norbury et al. 1988)

Birth

• Female gives birth standing/sitting up, with body hunched, pelvis forward, and tail behind her body (Poole 1975)
• Female usually licks the urogenital opening prior to and during birth, as well as the pouch opening (Poole 1975; Dawson 2013)
• During birth, the fetus breaks out of the amnion with small, sharp claws, and climbs up its mother’s fur into the pouch (takes about 3 min); the newborn then climbs down to the teats and attaches within a few minutes (Dawson 2013, except as noted)
  • The only body parts well developed at this time are the forearms, forepaws, claws, and nostrils (Staker 2006)
  • Uses senses of smell, touch, and direction (up/down) to navigate into the pouch
• Can breed throughout the year, but most births occur from late spring to early autumn (Oct-Mar) (Poole 1975; Norbury et al. 1988; Dawson 2013; Eldridge and Coulson 2015)
• Birth weight: about 0.82 g (0.03 oz) (Poole 1975; Dawson 2013)
• Also see "Newborn and pouch young" in Life Stages

Pouch cleaning

• Female holds pouch open with forepaws and licks to make the pouch soft and moist (Dawson 2013)
  • Begins during the last week of pregnancy and becomes most intensive 1-2 hours before birth
• Occurs when pouch is unoccupied, or if female has young, the joey waits impatiently outside the pouch (Staker 2006)

Protection of joey

• Pouch provides warmth and physical protection (Staker 2006)
  • Very young joeys cannot yet control their body temperature and require a humid environment for development
• Female macropods do not tolerate the joeys of other mothers; may jump on or bite them (Staker 2006)
  • Ensures that each joey stays with its mother
  • Cases of adoption behavior have been observed in the eastern gray kangaroo (King et al. 2015)

Milk nutrition

• Macropod joeys receive a different milk while in the pouch compared to when they are out of the pouch; the nutrients they receive change as they develop (Staker 2006)
  • Females can produce two kinds of milk at once in order to nurse two joeys at once: one tiny joey from the current year and a fully developed joey from the previous year (Sarah Garnick, personal communication, 2017)

Newborn and pouch young (kangaroos, general, unless otherwise noted)

• Undeveloped newborn remains strongly attached to one of its mother’s four teats until far along in development (Staker 2006)
  • Stays deep inside the pouch as body parts develop
  • This stage comprises less than 40% of the joey’s pouch life
• Eyes, ears, hind legs, and tail develop; without fur, however, the joey only pokes its bald head out of the pouch to begin visually experiencing the world (Staker 2006)
• After a joey grows fur and can regulate its body temperature, it begins standing and hopping for short periods of time, and starts eating solid foods (Staker 2006)
  • A joey’s first emergence from the pouch usually occurs at night (Staker 2006)
• Young spend about 11-11.5 months in the pouch (Staker 2006; Eldridge and Coulson 2015)
  • In one captive study, western gray kangaroo young first left the pouch at about 298 days old and left the pouch permanently at about 320 days old (Poole 1975)
    • Duration of time spent in pouch possibly varies among subspecies (Poole 1975), but this observation needs confirmation

Juvenile

• After leaving the pouch permanently, a young western gray kangaroo accompanies its mother on foot; nurses until after weaning (Eldridge and Coulson 2015)
• Weaned at about 18 months (Dawson 2013); range: 17-19 months (Staker 2006)
  • Young become nutritionally independent with an increase in spring vegetation (autumn rains help with lactation/weaning success) (Norbury et al. 1988; Arnold et al. 1991; Dawson 2013)
• Juvenile activities (Staker 2006)
  • Learn what foods to eat
  • Interact with other out-of-pouch joeys
  • Practice and refine hopping technique

Adult

• Males reach adulthood at 45-50 kg (99-110 lb) or about 5 years old (Dawson 2013)
• Males begin breeding successfully from 55-60 kg (121-132 lb) or 6-7 years old (Dawson 2013)
  • Only about 5% of males survive to this stage in the wild

Wild populations

• Not reported
• Males older than 10 years are rare (Dawson 2013)
• Females older than 12 years are also rare (Sarah Garnick, personal communication, 2017)

Managed care

• No AZA estimates

Survival rates

• High mortality between 0 and 4 years old (Dawson 2013)
• High mortality in young kangaroos between pouch exit and weaning (Arnold et al. 1991; Dawson 2013)
• Higher mortality in males than females, as in other kangaroo species (Dawson 2013)
  • About half of females and even more males die before reaching breeding age/full adulthood; reasons for this trend are unclear (Dawson 2013)
  • During periods of increased male-male competition, males experience low nutritional reserves and are at risk during dry times (Dawson 2013)

Poor nutrition (Dawson 2013, except as noted)

• Occurs during times of drought, flooding, and overgrazing (within high density populations and in competition with other species)
  • Norbury et al. (1988) report that 58% of western gray kangaroos in a northwest Victoria population survived a 1981-1983 drought
• Growing kangaroos have limited energy reserves; vulnerable to nutritional deficiencies
• Types of individuals affected
  • Young individuals out of the pouch and approaching weaning
  • Young males about to mature and breed for the first time
  • Old individuals that have extreme tooth wear or are otherwise unable to forage successfully

Predators

• Tasmanian wolf/Tasmanian tiger (now extinct) was probably their main predator before the arrival of the dingo; dingoes gradually replaced Tasmanian wolf as the main predator (Dawson 2013)
  • Dingoes, descendants of a semi-domesticated Asiatic wolf, became established in Australia 4,000 years ago (Parsons et al. 2007; Dawson 2013)
• Dingoes have a significant impact on kangaroo populations in some parts of Australia (Dawson 2013)
  • Dingoes viewed favorably by some Queensland beef producers who believe dingoes control pests, including kangaroos (Dawson 2013)
  • “Dog proof fences” used in some regions by ranchers to protect sheep from dingoes; these exclusion fences also protect kangaroos (Dawson 2013)
• Large male kangaroos are “essentially immune to natural predators,” but breeding females with young, as well as small males are more vulnerable and use less open habitats (MacFarlane and Coulson 2007)
• European red foxes and Wedge-tailed Eagles are also thought to contribute significantly to young kangaroo mortality, though more research is needed (Arnold et al. 1991; Dawson 2013)
• Limited predation on kangaroos living in protected areas on Kangaroo Island (Blumstein and Daniel 2002; Staker 2006)

Accidental death

• Collisions between motorists and kangaroos (and other macropods: wallabies and rat-kangaroos) occur frequently on Australian roads (Klöcker et al. 2006)
  • Kangaroos may be attracted to the vegetative cover and food near roadways
    • Eastern gray kangaroo study: Coulson et al. (2014)
  • In a study by Klöcker et al. (2006), gray kangaroos were hit less often than other kangaroo species
    • By having a more diverse diet, gray kangaroos may be less attracted to pasture grasses growing near roadways
    • Appear to spend less time grazing near roadways
    • Most gray kangaroos found dead in this study were young (5 years old or younger)
  • Collisions put kangaroos and motorists at risk
    • Costs of collisions
      • Designing vehicles to protect motorists (air bags, bull bars, etc.) makes vehicles heavier and less fuel efficient
      • Road maintenance
      • Potential impacts to tourism (unsightly roadkill)
    • Counter-measures to prevent collisions (usually only viable solutions in small areas or over restricted periods)
      • Noise-making devices
      • Driver education
      • Attempts to draw kangaroos away from roadways using food
      • Fences and roadway under/overpasses to alter kangaroo movements (see Movements and Dispersal)
      • Other repellants

Diseases

• Kangaroos considered very healthy in their natural habitats (Dawson 2013)
  • Evidence from health inspections of kangaroo meat processed for export
• Extreme environmental conditions (e.g., drought, flooding, extreme temperatures) stress the body systems of kangaroos, making them more susceptible to dying from diseases (Dawson 2013)
• Diseases (non-comprehensive list)
  • Ross River virus (carried by mosquitos) (Dawson 2013)
  • Q-fever (caused by bacteria Coxiella burnetii) (Dawson 2013)
  • Rare outbreak of choroid blindness (caused by Wallal virus, transmitted by midges) (Dawson 2013)
    • Western gray kangaroos more affected than red kangaroos or euros
  • Toxoplasmosis (protozoan disease) (Dawson 2013)
  • ‘Lumpy jaw’: chronic infection of the jaw bones that can give rise to septicaemia (caused by bacterium Fusobacterium necrophorum) (Dawson 2013)
• For information on diseases observed in managed care, see Staker (2006)

Parasites (non-comprehensive list)

• Nematode worms found in connective tissues (Pelecitus roemeri), blood (Babesia), and in the gastrointestinal tract (host-specific, do not transfer to other species) (Dawson 2013)
  • Kangaroos often carry high parasite loads, but these do not appear to impact their health (e.g., juvenile eastern gray kangaroo study by Cripps et al. 2014)
• Fleas, ticks, and mites (Staker 2006)

As a kangaroo joey grows, the nutrients in its mother's milk change.

Image credit: © Luke Shelley at Flickr. All rights reserved. Used with permission from the artist.

Image location: Kangaroo Island, Australia