Seasonal variations in reproductive hormones in free-ranging echidnas (Tachyglossus aculeatus): Interaction between reproduction and hibernation

We measured the reproductive steroids testosterone and progesterone in free-ranging adult echidnas over several years. For months other than June-August, the mean progesterone concentration was 0.18 ± 0.12 ng ml−1 (n = 14), and all blood samples taken from active female echidnas in June-August had progesterone concentrations above 0.5 ng ml−1. The highest progesterone value measured was 13.4 ng ml−1 in a pregnant female several days before egg-laying. For months other than June-August the mean testosterone concentration was 0.09 ± 0.05 ng ml−1 (n = 13). During June-August all active sexually mature males had testosterone concentrations in excess of 0.2 ng ml−1 and were found in mating groups at some time during this period. The highest plasma testosterone concentration measured was 4.62 ng ml−1.