Seasonal Pattern of Androgen Secretion in the Male Platypus, Ornithorhynchus anatinus, in the Upper Barnard River, New South Wales.

Abstract

The seasonal pattern of androgen secretion in free-ranging male platypuses was determined in samples of peripheral blood plasma and rectal contents collected between February and November 1996, from animals captured in the Upper Barnard River, New South Wales. Cortisol concentrations in peripheral blood were also measured and seasonal changes in body condition were assessed. Androgen concentrations in samples from the different sources all followed a distinctly seasonal pattern, being low from February to June, rising in July to reach the highest values in August before reducing to lower values by September. The high concentrations occurred within a relatively narrow time frame and appeared to be well synchronised among individuals. Within animal comparisons showed that androgen concentrations in excreta were highly correlated with values for blood. Cortisol concentrations were higher in July and August than other months. Males lost body condition during this period (as indicated by changes in the Tail Volume Index) and it is suggested that they were under increased stress at this time due to rivalry between males around the mating season.