Based on studies in captivity, a female platypus decides when courtship and mating are going to occur (Thomas et al. 2018b). As shown below, this typically results in the male grasping the tip of her tail in his bill and swimming with her in a tight circle or being towed behind her as she twists and turns near the water surface (Burrell 1927; Thomas et al. 2018b).
Mating can occur either while both animals are supported in shallow water by a structure (such as a partly submerged log) or while they’re floating in deeper water (Burrell 1927; De-La-Warr and Serena 1999; Easton et al. 2008; Thomas et al. 2018b) and may finish in less than a minute (Easton et al. 2008). A number of platypus mating postures have been described. In captivity, a relatively large male (1.6 kg) mounted his partner from above and behind, wrapping his tail beneath her body and grasping her hind feet and back with his front feet to maintain his position. In contrast, a smaller male (1.1 kg) lay on his side next to his partner while using his bill to grip her neck and his hind feet to grip her body (Thomas et al. 2018b). Pairs that mate while floating in the water may end up upside down relative to one another (while facing either the same way or in opposite directions), forcing them to rotate around their long axis so each can breathe in turn (Burrell 1927; De-La-Warr and Serena 1999; Easton et al. 2008).
A female platypus starts gathering material for nest-building about 1-2 weeks after mating. She uses her bill to gather grass and leaves from the channel, then passes the material under her body to the tail, which curls forward to hold the bundle as the female swims to her nesting burrow (as shown at left).
She continues to gather nesting material for 2-5 nights, finishing shortly before she retires to the burrow to lay and incubate her clutch of eggs (Thomas et al. 2018a). The completed nest takes the form of a hollow sphere or cup (Burrell 1927; Thomas et al. 2018a). Because wet vegetation is used to build a platypus nest, its main role is probably to maintain humidity in the burrow so eggs and small hairless juveniles don’t dry out when their mother has to leave the burrow to find food.
Photos courtesy of P. Walsh (top left), M. Kirton (top right) and J. Davey (bottom)
LITERATURE CITED
Burrell H (1927) The Platypus. Angus & Robertson: Sydney.
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.
Thomas J, Handasyde K, Parrott ML and Temple-Smith P (2018a) The platypus nest: burrow structure and nesting behaviour in captivity. Australian Journal of Zoology 65, 347-356.
Thomas JL, Parrott ML, Handasyde KA and Temple-Smith P (2018b) Female control of reproductive behaviour in the platypus (Ornithorhynchus anatinus), with notes on female competition for mating. Behaviour 155, 27-53.