Hastings River mouse
Common name: Hastings River mouse
Scientific name: Pseudomys oralis
Conservation status: This species is listed as Vulnerable in Queensland (Nature Conservation Act 1992) and Endangered nationally (Environment Protection and Biodiversity Conservation Act 1999).
The Hastings River mouse is a rat-sized native rodent, and so it is actually much larger than the term ‘mouse’ conveys. Adults weigh 80-120g, with a head-body length of 12-16cm and a tail length of 11-15cm.
The fur is brownish grey on top and buff to greyish white underneath. The hairs are slate-grey at the base when the fur is parted. The species may be confused with other rodents, especially the native bush rat Rattus fuscipes, which often occurs in the same habitat.
The Hastings River mouse is distinguished by its protruding eyes, narrow black eye-ring, distinctly rounded (‘Roman’) nose, white fur on the feet, bicoloured tail (dark skin above, light under) and obvious, wispy tail hairs that are pale-coloured under the tail and dark on top. The bush rat has a clearly ringed tail, typical of all native and introduced rats, and the hairs on its tail are shorter and less obvious.
Female Hastings River mice have four teats in the groin area, whereas rats have eight or more distributed between the chest and belly. Unlike Rattus species, the Hastings River mouse lacks a strong smell and is much more docile and easy to handle.
Habitat and distribution
The Hastings River mouse has been recorded from numerous scattered localities from near Muswellbrook in central east New South Wales to north of Cunningham's Gap, near Warwick in south-east Queensland. In 1975, bone material from the Hastings River mouse was also found in relatively fresh owl pellets collected from a cave near Mapleton on the Sunshine Coast of south-east Queensland, but no living individuals have ever been recorded from this region. Most sites are in New South Wales, but several important populations are present in Queensland. At many sites where the species occurs, it apparently exists in low abundance (e.g. less than one animal per hectare), and often only one or two individuals are trapped during surveys.
Few people have the privilege of seeing this animal because of its relative scarcity, secretive behaviour and nocturnal lifestyle, and because of where it lives. The Hastings River mouse is restricted to upland forests at elevations between 300m and 1250m (with most records above 500-600m), where it is confined to open forest and woodland with a grass, sedge, mat-rush, fern or heath understorey in close proximity to shelter. In south-east Queensland, it is generally found in grassy, dry or wet open forest close to rainforest and may even use the rainforest margins. Nationally, the largest populations are found in habitats that have been unburnt for at least five to ten years and that offer permanent shelter in or adjacent to feeding areas. Typically, these habitats possess a dense ground layer vegetation, comprising grasses, sedges, mat-rushes, ferns or heath.
Although some of the Queensland populations currently known (in Lamington National Park and Main Range National Park) inhabit ridge tops and slopes, the Hastings River mouse has also been recorded in minor drainage lines, gullies, swamps, seepages and grassy flats with good soil moisture (at least on a seasonal basis). The species requires some refuge from fire.
Life history and behaviour
The Hastings River mouse is not known to excavate its own burrows but depends on natural shelter opportunities offered by logs, hollows in tree butts, tree-root holes, rock cavities and epiphytes growing near ground level. These provide both daytime refuge and breeding sites secure from predators. Males use several nest sites within a permanent home range of up to 2ha, while average female home ranges are approximately 1ha. Captures of known female individuals at the same spot or close by over several years demonstrates that a high degree of site fidelity exists in this sex.
Breeding occurs from August to March, although commencement within this period can vary from year to year. Sexual maturity is reached at one year, with females capable of between one and three litters during the breeding season. Even though four teats are present, average litter size is estimated to be between two and three young. Limited data suggest females live longer in the wild than males, with some females living for three years and breeding in successive seasons.
The diet of the Hastings River mouse is approximately 64 per cent seed and fruit, 26 per cent leaf and stem, six per cent insect and four per cent fungus. Native grasses and sedges form a large part of the diet. By its consumption of ectomycorrhizal truffle-like fungi and the subsequent dispersal of spores in its faecal pellets, the Hastings River mouse may provide important ecosystem services for the various forest environments it inhabits.
Evidence exists of a decline in the Hastings River mouse distribution and abundance since European settlement. The Hastings River mouse is threatened by a number of interacting and compounding processes including altered fire regimes, habitat clearing, introduced predators, grazing and timber harvesting. At certain sites where they were previously found, the Hastings River mouse has not been recaptured following wildfire or understorey burns. All these sites lacked extensive rocky refuges, with the Hastings River mouse having to rely on dense vegetation, hollow logs and tree-butt hollows for shelter. At other sites, no Hastings River mice were recorded until periods of two years or more after wildfires. Planned burns are principally used by graziers to promote pasture development and by forest managers to reduce the risk of wildfire. Prescribed burns may also be necessary as a management tool at some Hastings River mouse sites to reduce wildfire risk and prevent replacement of grassy ground cover by trees and shrubs over the long term.
In some areas of its distribution, the Hastings River mouse reaches peak abundance approximately five to ten years or more after fire, when food plant species richness, density of vegetation cover under 1m tall and the presence of fire refuges are greatest. Timber harvesting and associated burning have the potential to impact on the species by reducing shelter provided by hollow logs and large old trees with butt cavities.
Cattle grazing of occupied open forests threatens the Hastings River mouse by removal and trampling of food species (palatable herbs, sedges, grasses and mat-rushes), also leading to a reduction in available cover. Further work is required in the Queensland part of the species’ range to determine what fire and grazing regimes are tolerable or optimal for the Hastings River mouse.
Specific threats to the Hastings River mouse include:
- weed invasion (e.g. by exotic legumes, causing changes to ground storey composition and the resulting availability of food resources)
- habitat degradation by feral pigs
- predation by cats and foxes
- inappropriate road maintenance practices (e.g. deposition of spoil in known or potential habitat)
- edge effects associated with clearing and agriculture
- road construction activities, particularly where this facilitates the penetration of forests by feral predators (e.g. foxes and cats)
- fragmentation of habitat, increasing the distance that dispersing individuals must move between remnant habitat patches and exposing them to greater risk of predation
- hydrological and vegetation changes due to mechanical disturbance (e.g. mining)
- climate change, leading to an increased frequency and severity of drought and wildfire (in turn, causing a decline in both understorey condition and available food resources or the total loss of all ground layer vegetation and shelter).
As part of national recovery efforts for this species, the department has conducted long-term monitoring of two known subpopulations and survey work to locate new subpopulations in Queensland. This work has focused on the Gambubal section of Main Range National Park and Lamington National Park.
All populations are small, with some shown to be genetically isolated and distinct. Evidence suggests that the Hastings River mouse is a poor disperser with limited ability to colonise new areas. The largest known population is from the Gambubal section of Main Range National Park, where a PhD research project in the 1990s found an average of twenty-nine individuals from a 9-ha trapping grid. At the time of this research, the average density of this population was 3.2 animals per hectare (range 1.1 to 5.3), and was highest during the winter and spring.
It is hoped that the results of the monitoring program will reveal changes in abundance of the resident populations in relation to factors such as vegetation condition, climatic variation and fluctuating numbers of other native rodents, which may compete with the Hastings River mouse. Identification of threatening processes (inappropriate fire regimes, grazing, feral predators) and development and implementation of management actions to address these threats are other important components of this work.
The Recovery plan for the Hastings River mouse (Pseudomys oralis) sets out research and management actions needed to support the recovery of the species.
Below are recommendations to address selected threats to the Hastings River mouse, thereby assisting recovery of the species. However, these recommendations should be considered against local conditions, regional ecosystem values and this species’ habitat requirements.
Using buffers - No vegetation clearing should occur on sites where the Hastings River mouse is known to occur. In particular, conserve all trees with hollow butts and all logs and fallen timber with a diameter of 30cm or more.
Feral animal and weed control - Control or eradicate weeds, feral pigs, foxes and feral cats where the Hastings River mouse occurs. (Refer to ‘Related information’ for website links providing information on weed and pest animal management, including details on prevention and various methods of control, as well as local contact details.)
Sustainable grazing - Grazing should be excluded from the sites where the Hastings River mouse is known or is likely to occur.
Fire management - On the sites where the Hastings River mouse occurs, fire regimes should include the following:
- no prescribed burning is undertaken during the breeding season from August to March
- the interval between fires is five to ten years or greater
- a mosaic of burnt and unburnt areas is created on the site so at most only one-third of the site is burnt at any one time, with a minimum of one-third always left unburnt for at least five years.