Size, seasonal weight change and growth in Platypuses, Ornithorhynchus anatinus (Monotremata: Ornithorhynchidae), from rivers and lakes of New South Wales.

Abstract

Platypuses captured in various water bodies in New South Wales were weighed and measured. There was considerable variation in both weights and lengths of animals measured from the different localities, with those from the Murrumbidgee River being larger than those from any other area. Mean lengths of adult males ranged between 53.3 ± 4.0 cm for individuals from Childowla on the Murrumbidgee River to 46.4 ± 0.5 cm for individuals from the Barnard River, while adult female mean lengths ranged between 47.6 ± 0.4 cm to 40.1 ± 0.2 cm for animals from the same localities. In some areas there was significant variation in weights with seasons, with either males or females losing weight in winter and gaining it during the following summer and early autumn. The highest mean weights for both males and females were again those for animals from Childowla (in February), being 2115 ± 95.7 g and 1398 ± 34.8 g respectively. Juvenile Platypuses emerged from nesting burrows around February in the Shoalhaven River at 81-88% of adult length, and 56-67% of adult weight for that month. After an initial spurt between February and April, growth was retarded in these animals during winter. Juvenile females grew rapidly during their first spring and reached adult size by the following January. Juvenile males also grew during this period but did not reach full adult size by this month. They were still recognisable as subadults using spur morphology. Possible reasons for the observed differences in size between areas are discussed.