Use of stream and river habitats by the platypus, Ornithorhynchus anatinus, in an urban fringe environment

Radio-telemetry was used to monitor movements and burrow usage by O. anatin us living in the Yarra River catchment, about 20 km east-north-east of the central business district of Melbourne, Victoria. The home ranges of six ad ult or subadult animals were 2.9-7.3 km (mean +/- s.d. = 4.6 +/- 1.6 km) lo ng, with individuals travelling up to 10.4 km (males) and 4.0 km (females) in a single overnight period. The mean home-range length of adult/subadult animals was significantly greater than that of juveniles (1.4-1.7 km, mean +/- s.d. = 1.55 +/- 0.2 km, n = 2). The animals utilised two drainage chann els as well as 11.8 km of natural waterways, including the Yarra River (5 k m), Mullum Mullum Creek (4 km) and Diamond Creek (2.8 km). Several animals travelled repeatedly below one-lane and two-lane bridges, confirming that t hese structures are not inherent barriers to platypus movement. In total, 5 7 platypus burrows were described, including 26 along the river, 29 along t he creeks and 2 along drains. The horizontal distance from the water's edge to burrow chambers was 0.4-3.7 m (mean +/- s.d. = 1.5 +/- 0.9 m, n = 41), with burrows found only in banks extending greater than or equal to 0.5 m a bove the water. Platypus burrows occurred significantly more often than exp ected along undercut banks and in association with moderate-to-dense vegeta tion overhanging the water, and significantly less often at sites where ban ks had a convex profile at water level. As well, the amount of cover provid ed along the bank by shrubs/small trees and the ground Payer of vegetation was significantly greater than expected at platypus burrows along the river . These attributes are believed to help conceal burrow entrances from preda tors as well as reduce burrow damage through erosion.