Breeding in a free-ranging population of platypuses, Ornithorhynchus anatinus, in the Upper Shoalhaven River, New South Wales -: a 27 year study

A total of 150 captures of lactating platypuses (97 individuals) were made over a period of 27 years in the study area. The proportion of lactating females from December samples ranged from 18 to 80% (mean 43.4 +/- 17.7%; n = 21 breeding seasons). The percentage of juveniles in samples taken at the seasons when young were leaving the nesting burrows varied from 0-63% (mean 34.4 +/- 17.9%; n = 22 breeding seasons). Only 8.8% percent of captured juvenile females went on to breed in the area; one bred in its second breeding season after emergence but two others did not breed until at least their 4(th) breeding season. Some females bred during at least 2-3 consecutive breeding seasons but others failed to breed in consecutive years. The percentages of females lactating in the months of September to April indicated a spread in the breeding season. Lactation in the wild was apparently shorter than reported in captivity, lasting more than 3 but less than 4 months. The majority of variation in breeding activity and recruitment could not be explained in terms of drought or observed riverine and riparian changes during the study.