Platypus numbers and reproductive success are most likely to be limited by the availability of nutritious food, mainly in the form of aquatic insects and other small aquatic prey. In turn, production of platypus food resources is strongly influenced by bank and channel habitat quality.
A positive relationship has been found to exist between platypus abundance or activity and the following habitat features:
- Indigenous trees (eucalypts and wattles) growing on the banks, especially large and partly undercut trees growing next to the channel (as shown above) (Holwell et al. 1998; Worley and Serena 2000; Serena et al. 2001)
- The percent of the channel shaded at midday (Holwell et al. 1998; Worley and Serena 2000)
- The amount of cover provided by shrubs and lower-growing plants, especially those overhanging the water (Ellem et al. 1998; Worley and Serena 2000)
- Stream and river banks that are both well-consolidated by plant roots and undercut to a depth of 8 centimetres or more (Serena et al. 2001)
- Relatively coarse inorganic bottom materials, such as gravel, pebbles, cobbles and large rocks (Serena et al. 2001; Grant 2004)
- Coarse organic materials in the channel, such as branches, bark, twigs and leaves (Holwell et al. 1998; Worley and Serena 2000; Serena et al. 2001; Koch et al. 2006)
- Water depth = 1 to 6 metres (ideal depth = 1 to 3 metres) (McLeod 1993; Bethge et al. 2003; Grant 2004)
- Sizable pools located along the channel (Ellem et al. 1998)
- Backwaters that are directly connected to a river or stream (Gust and Handasyde 1995)
Platypus populations sometimes occupy water bodies that are more or less lined with willows. Nonetheless, a strong negative relationship has been demonstrated to exist between the occurrence of willows and the distribution of platypus foraging activity (Serena et al. 2001). The creek where this research took place was relatively small and the willows were quite old and well established, so much of the channel under willows was lined by a thick mat of tough, fibrous roots – undoubtedly making it more difficult for a platypus to detect and capture prey than would otherwise be the case.
From a platypus’s viewpoint, other negative habitat features (as illustrated at left) include a prevalence of bare soil on the banks, large amounts of unconsolidated sediment such as sand deposited in or next to the channel (indicative of active erosion farther upstream), and large amounts of bare clay in the channel bed (indicative of active erosion at the site) (Worley and Serena 2000; Serena et al. 2001; Koch et al. 2006).
In rural landscapes, poor platypus habitat quality is often mainly driven by insufficient plant cover – particularly on the banks but also along adjoining gullies. In many cases, this was initiated by historical land clearing and continues due to excessive ongoing use by livestock and/or rabbits. Radio-tracking studies have confirmed that a platypus burrow may be abandoned when cattle tread on the bank where the burrow is located, presumably due to soil compaction (McLeod 1993). In addition, uncontrolled livestock access typically causes bank vegetation to disappear as plants are trampled and eaten. Cattle that have enter a natural channel are also likely to urinate and defaecate in the water, thereby degrading water quality both at the site and farther downstream.
In urban landscapes, poor platypus habitat quality is commonly driven by rapid runoff of stormwater from impermeable surfaces such as roofs and roads, especially when the runoff is carried by concrete pipes or drains directly to natural channels, resulting in urban stream syndrome.
Photos: APC
LITERATURE CITED
Bethge P, Munks S, Otley H and Nicol S (2003) Diving behaviour, dive cycles and aerobic dive limit in the platypus, Ornithorhynchus anatinus. Journal of Comparative Physiology Part A 136, 799-809.
Ellem BA, Bryant A and O’Connor A (1998) Statistical modelling of platypus, Ornithorhynchus anatinus, habitat preferences using generalised linear models. Australian Mammalogy 20, 281-285.
Grant T (2004) Depth and substrate selection by platypuses, Ornithorhynchus anatinus, in the Lower Hastings River, New South Wales. Proceedings of the Linnean Society of New South Wales 125, 235-241.
Gust N and Handasyde K (1995) Seasonal variation in the ranging behaviour of the platypus (Ornithorhynchus anatinus) on the Goulburn River, Victoria. Australian Journal of Zoology 43, 193-208.
Holwell G, Serena M and Williams GA (1998) Ecology and conservation of platypus in the Wimmera River catchment: II. Results of radio-tracking studies, winter 1998. Report to Earthwatch Australia and Rio Tinto Project Platypus by Australian Platypus Conservancy: Whittlesea VIC.
Koch N, Munks SA, Utesch M, Davies PE and McIntosh PD (2006) The platypus Ornithorhynchus anatinus in headwater streams, and effects of pre-Code forest clearfellling, in the South Esk River catchment, Tasmania, Australia. Australian Zoologist 33, 458-473.
McLeod AL (1993) Movement, home range, burrow usage, diel activity and juvenile dispersal of platypuses, Ornithorhynchus anatinus, on the Duckmaloi Weir, N.S.W. Bachelor of Applied Science Honours Thesis, Charles Sturt University: Bathurst NSW.
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: Whittlesea VIC.