The presence of logs, large branches and other woody debris in the water is a very positive habitat feature for platypus populations, contributing to foraging success. Sizable debris piles sometimes also provide these animals with sheltered places to sleep (Serena 1994).
The Australian Platypus Conservancy has conducted three studies to investigate whether the amount of woody debris differs at sites associated with routine platypus usage and those sites where little platypus usage occurs. In each case, the amount of woody debris is estimated below as the number of logs and large branches projecting above the water surface in 100 metres of channel during normal base flow.
Channel segments that were regularly used by radio-tagged platypus contained on average 21 logs and large branches (≥ 20 cm in diameter at the surface) in Running Creek (Yarra River system, Serena et al. 2001b) or 26 logs and large branches (≥ 10 cm in diameter at the surface) in the Little Yarra River (Yarra River system, Serena et al. 2001a). Similarly, channel segments along the upper Wimmera River in western Victoria that supported reasonably high amounts of platypus usage held on average 22 logs or branches (≥ 20 cm in diameter at the surface) (Worley and Serena 2000).
In addition, research has found that adding large items of dead wood to the Little Yarra River resulted in macroinvertebrates rapidly colonising the new material and the frequency of platypus foraging to increase significantly where wood was deposited (Coleman 2006).
What can be done to protect the platypus?
- Logs and large branches should be retained whenever possible in creeks, rivers and lakes in order to contribute to the quality of platypus habitat.
- Based on the studies described above, consideration should be given to augmenting the amount of instream woody habitat along creeks or small rivers where fewer than 20 logs or sizable branches project on average above the surface in 100 metres of channel during normal base flow. A potentially inexpensive approach may be to cut through fallen trees that bridge the channel or otherwise lie mainly out of the water to submerge more of their volume. To help inform future management, programs that augment woody debris should ideally include a monitoring component to assess environmental costs and benefits.
Photos courtesy of P. Sandercock (above), APC (below)
Coleman R (2006) Ecological and physical responses to large woody debris reintroduction in the Little Yarra River, Victoria, Australia. MSc Thesis, Monash University.
Serena M (1994) Use of time and space by platypus (Ornithorhynchus anatinus: Monotremata) along a Victorian stream. Journal of Zoology 232, 117-131.