Modelling the Pattern of Platypus, Ornithorhynchus anatinus, Trappings in An Impounded Riverine Environment.

Abstract

A mark, release, and recapture study of a platypus (Ornithorhynchus anatinus) population is being carried out on the Duckmaloi Weir. The unusual features of these data are the continual arrival of new animals over the study period and the non-reappearance within two years of about 90% of all first-captured animals. One possible interpretation of these data is that the trapping experience may modify the mark-recapture outcomes. The possibility of observer interference has been discounted by demonstrating that time to recapture is Exponentially distributed, implying arrivals of animals into nets are Poisson distributed. Indeed time from recapture to second recapture is also Exponential, further suggesting that initial capture is not having an effect on subsequent recaptures of O. anatinus in the Duckmaloi River. These conclusions are corroborated by the distribution of the number of animals caught each night throughout the period 1986-1993 being shown to be Poisson. The subsequent modelling yields interactions between the predictors sex, age and seasons. The final outcome is that time between mark and recapture varies, since the sex response changes with age of the animals and with seasons.