A platypus is unlikely to be killed directly by wildfire even in the case of extreme fire events (McColl-Gausden et al. 2023; Serena et al. 2023). This likely reflects the fact that a platypus normally has access to numerous burrows providing ample protection from flames, smoke and heat (Serena et al. 1998). Similarly, the small aquatic organisms mainly eaten by a platypus are unlikely to be killed directly by fire, except possibly along small headwater streams (Gresswell 1999).
However, problems may potentially arise if major fire activity is followed by heavy rainfall before plants have a chance to regrow and replenish protective leaf litter on the ground. The resulting runoff from bare slopes can carry huge amounts of soil and ash into waterways. In the short term, this may degrade water quality to the point that fish and other organisms relying on gills (including a high proportion of platypus prey) are killed by a pulse of catastrophically low dissolved oxygen (Lyon and O’Connor 2008). Massive deposits of unconsolidated sediment in the channel will also degrade habitat quality, with Lyon and O’Connor (2008) finding that it took about two years for surplus sediment to disappear from their study area in northeastern Victoria.
Using traces of platypus DNA present in water as an indicator of platypus occurrence, McColl-Gausden et al. (2023) reported that platypus activity in an area may be reduced when a major fire event is followed by rainfall. However, the effect was found to depend on fire severity – though the modelled likelihood of platypus occupancy declined (as compared to pre-fire levels) at sites that were severely burned and then subject to high rainfall, platypus occupancy sometimes improved (again, as compared to pre-fire levels) when rain fell at less severely burned sites. Across all fire-affected sites, the predicted mean (or average) probability of pre-fire platypus occupancy was 0.78 (2 to 12 months before the 2019-2020 “Black Summer” wildfires began), dropping to 0.72 (within 6 months of the end of the 2019-2020 fires), and then rising to 0.79 (12 to 18 months after the end of the 2019-2020 fires).
Similarly, based on live-trapping surveys conducted in a river in northeastern Victoria before and after it was severely burned by wildfire in December 2019, Serena et al. (2023) found that platypus were consistently captured at every site where nets were set in surveys conducted 22 months before wildfire occurred, 5 weeks after the main fire event, and 35 weeks after substantial rain triggered mass movement of post-fire ash and sediment into the river. To access a copy of this paper, click here.
Importantly, platypus reproduction was highly successful in the first post-fire breeding season, with six juveniles captured at the four sites where nets were set in March 2021 (see photo of one of the young males above at right). Enough young animals were produced that population density would have doubled if all young animals had settled down locally. In contrast to the apparent resilience of this platypus population, native fish abundance dropped by nearly 90% in the same area after sediment and ash entered the channel.
The major loss of fish implies that many other gilled organisms – including many platypus prey species – would have died at the same time. How is it possible that platypus not only managed to survive the same fire-related impacts but went on to produce many healthy offspring? Two possible explanations were proposed by Serena et al (2023):
- Platypus occupying badly impacted parts of the river temporarily moved to less badly affected habitats (such as adjoining tributary streams) until invertebrate prey populations recovered.
- Platypus remained in badly impacted parts of the river and survived by consuming the remains of recently killed organisms (such as fish) or by consuming prey that remain largely unaffected by post-fire siltation (such as worms) or by using stored body fat.
More generally, the fact that the platypus has developed successful strategies for dealing with fire-related impacts is not particularly surprising, given that these animals have been around for millions of years and fires of varying intensity occur routinely throughout most of the platypus’s range (Murphy et al. 2013).
Photos: APC
LITERATURE CITED
Gresswell RE (1999) Fire and aquatic ecosystems in forested biomes of North America. Transactions of the American Fisheries Society 128, 193-221.
Lyon PJ and O’Connor JP (2008) Smoke on the water: can riverine fish population recover following a catastrophic fire-related sediment slug? Austral Ecology 33, 794-806.
McColl-Gausden EF, Griffiths J, Collins L, Weeks AR and Tingley R (2023) The power of eDNA sampling to investigate the impact of Australian mega-fires on platypus occupancy. Biological Conservation 286, 110219.
Murphy BP, Bradstock RA, Boer MM, Carter J, Cary GJ, Cochrane MA, Fensham RJ et al. (2013) Fire regime of Australia: a pyrogeographic model system. Journal of Biogeography 40, 1048-1058.
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, Lyon JP, Tonkin ZD, Lieschke J and Williams GA (2023) Differential impacts of a wildfire and post-fire sedimentation event on platypus and fish populations in a Victorian upland River. Marine and Freshwater Research 74, 86-94.