Studies have confirmed that a strong positive relationship exists between the amount of cover provided by shrubs, trees and low-growing plants on creek or river banks and the quality of platypus foraging and burrow habitats (e.g. Ellem et al. 1998, Serena et al. 1998, Worley and Serena 2000, Serena et al. 2001).
A self-sustaining corridor of dense riparian vegetation is of enormous value in stabilising banks and preventing erosion. Trees and overhanging shrubs shade the water and keep it cool in summer, thereby improving the availability of dissolved oxygen to macroinvertebrates that in turn are eaten by the platypus. Plants are also a crucial source of organic matter (fallen branches, twigs, leaves, buds and flowers) that helps to fuel the aquatic food web. In the case of urban waterways, a substantial corridor of trees and shrubs also acts to screen out noise and artificial light, trap litter and other pollutants, reduce trampling by humans and restrict access by unsupervised pets.
Some introduced plants such as willows can have a significant detrimental impact on platypus habitat quality (particularly in places where willow roots invade a large proportion of the channel). However, it is important to ensure that eradication programs for willows or other introduced weeds are designed to minimise the likelihood that bank erosion subsequently occurs. In addition, platypus survival may be compromised (particularly along narrow creeks) if predation risk increases as an unintended outcome of weed control activities.
What can be done to protect the platypus?
- Urban (or other) development should never be allowed to encroach unreasonably close to creeks and rivers where platypus occur. Whenever possible, a 50-metre-wide (or wider) vegetated buffer zone should be reserved on both banks to establish a self-sustaining riparian zone that meets the platypus’s needs as an apex predator in aquatic ecosystems.
- Unrestricted livestock access often causes bank habitats to become degraded, sometimes very severely. To protect populations of platypus and other aquatic wildlife (such as fish), creek and river banks should be fenced to restrict their use by livestock, ideally on a permanent year-round basis.
- Willows should be progressively removed from river catchments and replaced with indigenous vegetation to improve overall habitat quality. To minimise disturbance and potential erosion, willow trunks should be cut and hand-painted with herbicide while the root system is left intact to rot naturally; sites where willows have been removed should be replanted as soon as possible with appropriate native trees and shrubs.
- In cases where a weedy species dominates both banks of a creek or river for a considerable distance (e.g. 200 metres or more), consideration should be given to staging removal programs so the plant is eliminated from one bank in one year and the opposite bank in a later year.
- Herbicides used to control riparian weeds should never be allowed to enter the water, either directly or through storm run-off. Areas of bare soil caused by herbicide use should be planted (or reseeded) as soon as possible with appropriate indigenous species.
- To avoid damaging platypus burrows, use of heavy machinery within about 10-15 metres of the water’s edge should be avoided whenever possible in platypus habitats. Special care should be taken not to disrupt banks or cause them to become compacted in spring and summer when females are raising their young, particularly in places where platypus are abundant.
Photo: APC
Literature cited
Ellem B, Bryant A and O’Connor A (1998) Statistical modelling of platypus, Ornithorhynchus anatinus, habitat preferences using generalised linear models. Australian Mammalogy 20, 281-285.
Serena M, Thomas JL, Williams GA and Officer RCE (1998) Use of stream and river habitats by the platypus, Ornithorhynchus anatinus, in an urban fringe environment. Australian Journal of Zoology 46, 267-282.
Serena M, Worley M, Swinnerton M and Williams GA (2001) Effect of food availability and habitat on the distribution of platypus (Ornithorhynchus anatinus) foraging activity. Australian Journal of Zoology 49, 263-277.
Worley M and Serena M (2000) Ecology and conservation of platypus in the Wimmera River catchment: IV. Results of habitat studies, summer 1999. Report to Rio Tinto Project Platypus by Australian Platypus Conservancy.