Jacqui Hunter 
Our creek bank has been transformed into multi-story apartment blocks, with mezzanines, courtyards and well-trodden roads between the entrances. This real estate boom began along the creek, but has spread further into the bush. Piles of freshly overturned earth are the sign that the ‘ecosystem engineers’ are at work.
Rattus lutreolus, or native swamp rats, have taken up residence on our 2 acre property near McLaren Vale in the last couple of years, proliferating their dwellings along the creek to many neighbouring properties. We are told they love eating sour sob bulbs – so we may have them for a long time to come!
In trying to understand this native mammal phenomena, we have hosted a gathering of neighbours to share our experiences and strategies as our fruit orchards and neighbour’s seedling nursery are converted into fine dining restaurants. We have wandered our property with Hills and Fleurieu Landscapes Board Senior Stewardship Officer, Jacqui Best and Flinders University PhD student, Beth Treglown.
We also borrowed a wildlife camera from the Willunga Environment Centre to capture some tenancy action. As a result we have been discovering the pros and cons of our new tenants. This has led us to wonder if you, or someone you know may have observations or information to share and add to this knowledge.
Pros:
Swamp rats are ‘mycophagists’ and play an important role in supporting fungal networks in the soil and general ecosystem health. In her book, ‘Underground Lovers’, Alison Pouliot explains their impact:
“Mammals distribute spores, and their digging in search of truffles and tubers turn and renews soils. Ecologists dub them ‘ecosystem engineers’. Ecosystem engineers directly or indirectly influence the availability of resources for other species by maintaining, modifying or creating habitat. ….these mammalian mix-masters help incorporate surface litter into the subsurface, increasing nutrient cycling and water retention. This in turn provides a source of food and habitat for organisms under the ground. It is all part of the process of building up biological activity and the organic component of soils. This collectively increases the vigour and resilience of plants, and improves overall ecosystem function. The movement of soil, and increased heterogeneity creates new substrates, microclimates and niches for fungi and redistributes fungal spores……
The more water entering soil there is less run-off, thus reducing erosion. Plants in turn benefit from increased water availability and can more easily absorb nutrients. Digging mammals also affect seed dispersal and seedling success. Seedlings that grow in soil where there has been intensive digging activity do better than those that grow in less intensely dug soils.”
We have seen an improvement in the soil during our recent planting sessions. The soil structure and moisture content seems to be better than previous years, especially near the ‘Swampies’ condominiums.
Cons:
- Creek bed erosion. There is a high chance that parts of the creek banks will erode as the honey-combed tunnels fill with water and wash away.
- Undermining trees and shrubs to expose roots. I have refilled holes around some plants to attempt to save them from exposure. This has worked in some instances, with the swampies finding other places to go.
- Increase feral animal sightings. We have caught foxes and a cat on camera!
Pro or Con?
There has been a massive germination of fumitory seedlings on the mounds of freshly dug soil. We have sprayed these with a geranium spray which has knocked them out. We’re thinking that maybe this could be positive if we can reduce the weed seed load in the soil and replant with natives.
What are the longer term ramifications of this explosion of swamp rat numbers in the environment? How do we know what their population is? Do the number of holes represent their population or are they constantly creating the next McMansion?
Do they have an influence on the population of Rattus rattus?
How do we measure their impact? The good, the bad and the swampy!!
Upload photos to i-Naturalist of swamp rats. This will help build a data base of where they are and their impact.
References:
Pouliot, Alison. ‘Underground Lovers’, 2023, New South Publishing, Aust.
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