Figure 3. Time between final arousal from hibernation and egg-laying for 23 reproductive events from 13 echidnas, as estimated from internal (red circles), and external (blue circles) temperature loggers.

The reported gestation period for echidnas is 20–24 days [15]. Although three animals (3A61, 4057, 2753) were active for periods of up to 3 weeks before becoming pregnant, the majority of points lie between 20 and 24 days after the end of hibernation. In these cases the females must have become pregnant nearly immediately after the final arousal from hibernation, or were already pregnant. Echidna 0118 must have become pregnant during the previous euthermic period (see Figure 2), as was probably also the case for three of 5D5E's pregnancies.