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

Abstract

Radio-telemetry was used to monitor movements and burrow usage by O. anatinus 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 adult or subadult animals were 2.9–7.3 km (mean ± s.d. = 4.6 ± 1.6 km) long, 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 channels as well as 11.8 km of natural waterways, including the Yarra River (5 km), Mullum Mullum Creek (4 km) and Diamond Creek (2.8 km). Several animals travelled repeatedly below one-lane and two-lane bridges, confirming that these structures are not inherent barriers to platypus movement. In total, 57 platypus burrows were described, including 26 along the river, 29 along the 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 ≥ 0.5 m above the water. Platypus burrows occurred significantly more often than expected along undercut banks and in association with moderate-to-dense vegetation overhanging the water, and significantly less often at sites where banks had a convex profile at water level. As well, the amount of cover provided along the bank by shrubs/small trees and the ground layer of vegetation was significantly greater than expected at platypus burrows along the river. These attributes are believed to help conceal burrow entrances from predators as well as reduce burrow damage through erosion.