Home Range, Burrow Usage and Diel Activity of Platypuses on the Duckmaloi Weir, New South Wales.

Abstract

Platypuses, Ornithorhynchus anatinus, have been studied on the Duckmaloi River, New South Wales, in a long term mark-release-recapture project from 1986 to 1996. Some animals are recaptured regularly, while others are trapped only once. A high percentage of juveniles are never retrapped. New animals continue to be captured each year. Hence radio-tracking was employed to examine the movements of animals within the river system including their spatial utilisation of the Duckmaloi Weir. Concurrent studies on activity patterns and burrow usage were undertaken. Seventeen animals (I 0 juveniles, 2 subadults and 5 adults) were radio-tracked for various lengths of time between January and October 1993. Telemetric data revealed that radio-tagged animals were not recaptured on all possible occasions. Home ranges (length of river) varied from 0.5 km to 3.5 km. Home ranges of all animals, overlapped extensively, while core area overlap also occurred in the pool behind the Duckmaloi weir. One juvenile male dispersed 8.5 km upstream from the weir. Platypuses typically utilised areas when feeding with water depth between I to 2.5 m, rarely using areas less than 0.5 m deep. Juvenile platypuses were crepuscular and nocturnal, while adults, although mainly nocturnal also exhibited individual variations in diurnality. Although some individuals remained active throughout the night, others returned to burrows before re-entering the water. Animals commonly returned to certain burrow complexes with some exhibiting a higher degree of burrow site specificity than others. Certain burrows were used by nearly all radio-tagged animals over time while others were used by only a select number of individuals. Some animals tracked in the weir pool were found to share burrows.