Platypus (Ornithorhynchus anatinus) Fact Sheet: Reproduction & Development

Mating system

• Thought to be polygynous (needs confirmation with additional studies) (Bino et al. 2015; Grant 2015; Serena and Grant 2017)
  • Male venom gland size and male aggression increase during breeding
    • Suggests competition for females
• Social system not well known (Grant 2015)
  • See Social Behavior

Courtship behavior and copulation

• Mating rarely observed in the wild (De-La-Warr and Serena 1999; Grant 2015)
• Courtship
  • Video: courtship behaviors begin at 01:21
  • Male initiates most interactions (Hawkins and Fanning 1992; Grant 2007)
    • Searches territory for unmated females (Thomas et al. 2018)
  • At first, female avoids male; then reduces avoidance (Thomas et al. 2018)
  • Male and female dive and swim past each other (Grant 2015; Thomas et al. 2018)
  • Then, male and female grasp each other and roll several times (Grant 2015, and as noted)
    • Male grasps female by tail with bill (Fleay 1994b)
    • Pair swims in a tight circle (Fleay 1944b; De-La-Warr and Serena 1999)
  • Courtship behaviors may last less than a minute or half an hour or more, over several days (Grant 2007)
• Copulation (Grant 2015)
  • Male grasps female by tail with bill
  • Wraps his tail under the female’s body
  • Male moves forward, nuzzling and gripping female’s fur
  • In managed care, copulations have occurred over several days
• After copulation, female becomes solitary for nesting (Thomas et al. 2018)

General

• Sexual maturity
  • Both sexes physically able to reproduce in second breeding season after independence, but many begin breeding later (Grant 2007; Grant 2015)
    • Females may be four years or older (Grant et al. 2004; Grant 2007)
• Male reproductive organs and structures
  • Testes
    • Located in abdomen (Grant 2015)
    • Large (Nixon et al. 2016)
      • Suggests that males mate with multiple females
  • Sperm (Temple-Smith 1973; Grant 2015)
    • Thread-shaped
    • Reptile-like
    • Produced seasonally
  •  “Sperm bundles” form when heads bind together as sperm pass through the epididymis (Nixon et al. 2016)
    • Able to swim forward faster; likely improves ability to compete
      • Suggests a promiscuous mating system
    • Among mammals, unique to egg-laying mammals (platypus and echidnas)
• Female reproductive system
  • Only left side is functional (Grant 2015)
    • Similar to many birds and some reptiles
• Environmental factors
  • Rainfall influences reproductive success (Serena et al. 2014)
    • Affects amount of food available to breeding females

Breeding

• Breed seasonally (Temple-Smith 1973; Grant 2007; Grant 2015)
• Courtship, mating, and nest building occur in late winter to early spring (Grant 2007; Grant 2015)
  • Breeding cycle begins earlier in northern Australia and much later in Tasmania (Grant 2007)
  • Mating and egg laying: July-November (mainland Australia)
    • Mating as late as February in Tasmania
  • Emergence of young from burrow: December-April (mainland Australia)
• Not all females breed each year (Grant 2015)

Overview

(Grant 2015)

• Female lays eggs and incubates them in a nest within burrow chamber
• After hatching, mother nurses young by producing milk (like other mammals)
  • See “Nourishment of Young" in Parental Care, below

Gestation

• Gestation period
  • Approximately 21 days (Grant 2015)
• Clutch size
  • 1-3 eggs per breeding season (Grant 2015)
    • Two eggs most common

Egg incubation and hatching

• Egg description (Grant 2015)
  • Shape: nearly round
  • Size: approximately 14 x 17 mm (0.55 x 0.67 in)
• Incubation period
  • Approximately 10 days (Grant 2015)
• Female likely incubates the egg by adopting a curled-up posture (same as while sleeping), holding the egg between her abdomen and tail (Burrell 1927; Griffiths 1978; Grant 2007; Enjapoori et al. 2014)
  • Incubation is external (not in pouch, like echidnas)
• Young use egg tooth to break through eggshell (Manger et al. 1998)
• After hatching, extensive development occurs in the nest (Manger et al. 1998; Ferner et al. 2017)
• Little known about activities of mother platypus during incubation and weeks after hatching (Manger et al. 1998)

Nesting burrow

• Used to incubate and nurse young (Grant 2015)
  • Only female builds and uses nesting burrow
• Complex structure (Burrell 1927; Grant 2007)
  • Several passages and chambers
  • Tunnel length: 3-30 m (9-98 ft)
• Construction takes about 10 days (observations in managed care) (Grant 2015)
  • Nearly all nesting burrows constructed in earth banks in riparian vegetation (Grant 2007)
    • Up to 20-30 m (65-98 ft) away from stream edge (Koch et al. 2006)
    • Some occurrences of nests deep inside caves (Grant 2007)
  • Female gathers vegetation; carries it to burrow between hind feet and tail (Fleay 1944b; Grant 2015)
    • Lines nesting chamber with wet leaves, twigs, etc.
      • Humidity thought to prevent the eggs/nestlings from becoming too dry
• When young are too small to swim, mother blocks entrance tunnel with loose soil when she leaves to feed (Burrell 1927)
• Mother may be away from the burrow for long periods (up to multiple days as growing young require more milk) (Serena 1994)
• Young are suckled in nesting burrow for about four months (Grant 2015)
• Quickly become independent when emerge from burrow (Grant 2007, 2015)
  • Late January-April in mainland Australia
  • As late as May in Tasmania
• Also see Life Stages

Nourishment of young

• Lactation period
  • Late September to mid-March (southeastern mainland Australia) (Grant 2015)
  • 114-145 days (Grant and Griffiths 1992; Holland and Jackson 2002; Enjapoori et al. 2014)
• During breeding, a female’s mammary glands become large, fan-shaped structures (Grant 2007; Grant 2015)
  • Located under skin
  • Occupy most of the abdominal surface
  • Shrink outside of breeding season
• Position of young’s forefeet suggests they can hang onto mother’s fur and climb to mammary area to drink (Manger et al. 1998)
• Milk characteristics and composition
  • Color pink-white (Grant 2007)
  • High solid content: rich in whey proteins, carbohydrates, fats, and minerals (Grant 2007)
  • Antimicrobial
    • May protect hatchlings against infections (Enjapoori et al. 2014; Newman et al. 2018)
      • Lapping milk from mother’s skin makes young more vulnerable to bacterial infection, compared with mammals that suckle from teats
  • High concentrations of iron
    • Similar to echidnas (also adapted to reduced oxygen levels in burrow)
• Unclear whether juveniles continue nursing after emergence from burrow (Grant 2007)

Hatchling

• Major features of bill visible by five days after hatching (Manger et al. 1998)
• Webbing on forefeet fully formed by 24 days after hatching (Manger et al. 1998)
• Very short fur at 11 weeks after hatching (Manger et al. 1998)

Juvenile

• Remain in nesting burrow for 3-4 months after hatching (Fleay 1944b; Grant 2007)
• Emerge from nesting burrow in late summer or early fall (Grant 2015)
• Molar-like “milk” teeth of young/juveniles shed around the time young leave nesting burrow (Grant 2015)
  • Replaced by grinding pads made of keratin (in adults)
• Dense fur at six months after hatching (Manger et al. 1998)
• Juveniles appear to remain in natal area (Grant 2015; Thomas et al. 2019)
  • Some evidence from recapture data
• Typically disperse within a year (Grant 2015)
  • Some females (about 32%; Grant 2007) remain in natal area to adult age (Furlan et al. 2013; Bino et al. 2015)

Adult

• Reach adult size 12-18 months after emergence from burrow (Grant 2007)
• Males begin to produce venom at maturity (Whittington and Belov 2014)
  • See “Spurs and venom” in Sexual Dimorphism

Wild populations

• 7 to 14 years (Grant 2004; Grant 2015)
• In a study of three suburban areas (Serena et al. 2014):
  • Median longevity: 6 to 7 years

Managed care

• No AZA estimates

Survival rates

• Birth to independence
  • Not known (Grant 2015)
• Juvenile and adult survival rates (Bino et al. 2015)
  • Higher in adult females than adult males
  • Higher in juvenile females than juvenile males
  • In adults, influenced by weight and river flow
• Serena et al. (2014) observed an annual population loss of about 16% over 10 years in urban habitats near Melbourne
• Individuals succumb to heat stress and starvation during drought and during dispersal in juveniles (Grant 2007)

Predators

• Not well-known (Grant 2007)
  • Many reports anecdotal
• Native predators
  • Tasmanian devils (Munday et al. 1998) and raptors (e.g., Wedge-tailed Eagle (Marchant and Higgins 1993; Rakick et al. 2001) more likely to scavenge than to hunt platypus (Josh Griffiths, personal communication, 2018)
  • Isolated cases of predation by crocodiles and large native fish (Grant 2007)
  • Early naturalists also suggested goannas and carpet pythons (Grant 2007)
• Non-native predators
  • See Threats to Survival

Diseases

• Few diseases affect wild platypuses (Munday et al. 1998)
  • Some disease agents cause no symptoms or have no known effects (Whittington 1992; Whittington 1993a)
• Fungal pathogen, Mucor amphibiorum
  • Only pathogen known to cause significant disease and death in wild platypuses (Whittington 1992)
  • Only affects platypuses in Tasmania (Gust and Griffiths 2009)
    • Not confirmed from platypuses on mainland Australia
  • Causes an ulcerative skin condition (mucormycosis, a.k.a. ulcerative dermatitis) (Obendorf et al. 1993; Gust and Griffiths 2009; Connolly 2015; Macgregor et al. 2017)
• Other conditions
  • Nodules observed in foot webbing (Macgregor et al. 2017)
    • May be caused by foreign material, fungi, or possibly spiral bacteria
  • Lung infections (e.g., pneumonia), if normal gut flora become pathogenic (McColl 1983; Whittington 1993a)
• See Jackson (2003), Booth and Connolly (2008) and Macgregor et al. (2017) for additional disease descriptions

Parasites

• Ticks (McColl 1983; Macgregor et al. 2017)
• Nematodes (Spratt and Whittington 1989; Whittington and Spratt 1989; Spratt and Beveridge 2016)
• Trematodes (Jackson 2003; McColl 1983; Spratt and Beveridge 2016)
• For more information on parasites, see McColl (1983), Munday et al. (1998), Jackson (2003), Booth and Connolly (2008), Lunn et al. (2016), and Macgregor et al. (2017).

Museum model of a nesting female platypus, curled around her eggs to incubate them.

Nest and platypus specimen collected by Harry Burrell.

The platypus and the echidnas are the only living mammals that lays eggs.

Image credit: © National Museum of Australia. Creative Commons BY-SA 4.0.