Platypus courtship or mating behaviour in the wild has been recorded in late July and August in southern Queensland (Temple-Smith and Grant 2001), August and September in New South Wales (Burrell 1927), August to October in Victoria (De-la-Warr and Serena 1999; Easton et al. 2008), and as late as December in Tasmania (Roberts and Serena 2024). Platypus reproduction doesn’t rely on the formation of enduring pair bonds. Instead, males try to breed with as many females as possible, and females rear their young without any male assistance.
After mating, gestation of eggs takes an average 16 days, followed by an estimated 10-day incubation period (Thomas et al. 2020). Platypus eggs are 16-18 millimetres long and have a whitish shell with a papery or parchment-like texture, similar to those of lizards (Burrell 1927). A clutch of one to three eggs (most often two) is incubated in an underground nesting chamber, held between a female’s curled-up tail and her belly to keep them warm (Burrell 1927). The young are tiny and very immature when they hatch. Their exit from the egg is assisted by a prominent bump (or “caruncle”) at the end of the snout, an inwardly curving egg tooth and tiny claws on the front feet (Burrell 1927).
After hatching, the babies develop in the nesting burrow for approximately 3 months before entering the water for the first time in summer (on the Australian mainland) or autumn (in Tasmania) (Williams et al. 2013; Roberts and Serena 2024). While they’re confined to a burrow, they feed on a rich milk containing on average about 39% solids (as compared to 12% solids in cow milk) (Griffiths et al. 1984). A female platypus doesn’t have nipples, so babies slurp up milk secreted from two special patches of skin onto her belly fur. While suckling, a mother platypus may lie either on her side or on her belly (with the nestlings lying upside down beneath her); she will sometimes rub their bills with her own after they’ve finished eating, presumably to clean off any sticky residue (Thomas et al. 2020).
Juveniles are fully furred, well-coordinated and about 85% of their adult length when they first enter the water, as shown above (Grant and Temple-Smith 1983). Based mainly on observations made in captivity, they aren’t taught to swim or to find food by their mother, but have to master these skills on their own through trial and error.
Males and females both become mature at the age of two years, although a long-term study conducted along the upper Shoalhaven River in New South Wales concluded that less than half of all females breed on average in any given year (range = 18-80%) and some females may not raise their first litter until they are at least four years old (Grant et al. 2004). Along both the Shoalhaven River and urban streams near Melbourne, more young are produced in years when water flow has been plentiful in the five months before mating begins, suggesting that this is a crucial period for females to store fat in preparation for breeding (Serena et al. 2014; Serena and Grant 2017). Platypus reproductive success may also drop if substantial flooding occurs when juveniles are confined to nesting burrows or soon after they first emerge, presumably because young animals drown (Serena et al. 2014; Serena and Grant 2017).
Photos courtesy of Ann Killeen (top), Pete Walsh (bottom)
LITERATURE CITED
De-La-Warr M and Serena M (1999) Observations of platypus Ornithorhynchus anatinus mating behaviour. The Victorian Naturalist 116, 172-174.
Easton L, Williams G and Serena M (2008) Monthly variation in observed activity of the platypus Ornithorhynchus anatinus. The Victorian Naturalist 125, 104-109.
Grant TR and Temple-Smith PD (1983) Size, seasonal weight change and growth in platypuses, Ornithorynchus anatinus (Monotremata: Ornithorhynchidae), from rivers and lakes of New South Wales. Australian Mammalogy 6, 51-60.
Grant TR, Griffiths M and Temple-Smith PD (2004) Breeding in a free-ranging population of platypuses, Ornithorhynchus anatinus, in the upper Shoalhaven River, New South Wales – a 27 year study. Proceedings of the Linnean Society of New South Wales 125, 227-234.
Griffiths M, Green B, Leckie RMC, Messer M and Newgrain KW (1984) Constituents of platypus and echidna milk, with particular reference to the fatty acid complement of the triglycerides. Australian Journal of Biological Sciences 37, 323-329.
Roberts S and Serena M (2024) Use of consolidated time-lapse camera imagery to detect and monitor platypus (Ornithorhynchus anatinus) activity. Australian Mammalogy 46, in press. doi:10.1071/AM23045
Serena M and Grant TR (2017) Effect of flow on platypus (Ornithorhynchus anatinus) reproduction and related population processes in the upper Shoalhaven River. Australian Journal of Zoology 65, 130-139.
Serena M, Williams GA, Weeks AR and Griffiths J (2014) Variation in platypus (Ornithorhynchus anatinus) life history attributes and population trajectories in urban streams. Australian Journal of Zoology 62, 223-234.
Temple-Smith P and Grant T (2001) Uncertain breeding: a short history of reproduction in monotremes. Reproduction, Fertility and Development 13, 487-497.
Thomas JL, Parrott ML, Handasyde KA and Temple-Smith P (2020) Maternal care of platypus nestlings (Ornithorhynchus anatinus). Australian Mammalogy 42, 283-292.
Williams GA, Serena M and Grant TR (2013) Age-related change in spurs and spur sheaths of the platypus (Ornithorhynchus anatinus). Australian Mammalogy 35, 107-114.