The life history of an egg-laying mammal, the echidna (Tachyglossus aculeatus)

Echidnas have a low metabolic rate, and energy expenditure is reduced even further by the use of torpor and hibernation. Thus, echidnas appear to lie at the slow extreme of the fast-slow continuum, and this is reflected in many aspects of echidna life history: a long life, a long lactation period, and a single young that matures late. Reproductive activity occurs in mid-winter, shortly after arousal from hibernation. After a pregnancy of about 3 weeks the female lays a single egg into her pouch that hatches after 10-11 d. Initially, the young is incubated in the pouch. Later, it is left in the nursery burrow while the mother forages for ants, termites, and other invertebrates. Lactation lasts for 150-200 d, the duration differing significantly between geographic regions. Growth rates during late lactation are very high, and, when weaned, the young has reached about 40% of adult mass. The young loses mass before entering its first hibernation, which extends from early autumn to late spring. The young echidna reaches adult mass after about 3-5 years.