Let’s talk about egg laying mammals- sounds crazy but it’s true! There is a very small group of mammals that actually do lay eggs. They are called Monotremes which include the duckbilled platypus and the echidna.
The breeding season lasts from June through October. Male platypuses are polygmous, meaning they mate with more than one female during the breeding season. The females have two ovaries but strangely only the left one is functional. A typical platypus burrow entrance is 30 cm about water level but after mating the female digs a deeper and more elaborate burrow about 20 m deep. These elaborate burrows have several chambers and are blocked at intervals with plugs. This may act as a safeguard against rising water, predators, or for regulating humidity and temperature. Leaves on the bottom of the burrow act as bedding and retaining moisture.
Once the platypuses have mated, the eggs develop in utero for 28 days and then require 10 days of external incubation before hatching. She lays 3 thick leathery eggs, about 11 millimeters each, in one of her burrow chambers and curls around them. Incubation happens in 3 phases. 1st phase- the embryo has no functional organs and relies on the yolk sac for nourishment. 2nd phase- the embryo develops digits. 3rd phase- the egg tooth develops.
Once hatched the baby platypuses are blind, hairless, and vulnerable. They drink their mother’s milk for 3-4 months before emerging, once thye’re ready to swim. Interestingly, the female does have mammory glands but lacks teats. The milk is secreted through pores in the skin and runs down small groves where it pools on her abdomen. Here the young lap up the milk.
The breeding season lasts from the end of June through September. The males form “trains” where 2 to 10 males form a line and follow one another searching for females. Males may join several trains during the breeding season. The females have two ovaries and both are functional.
Two weeks after mating the female lays 1 egg, it’s soft and leathery and no bigger than a grape. She rolls this egg into a pouch on her abdomen. After 10 days in the pouch a baby echinda or puggle hatches.