Bolam's Mouse (Pseudomys bolami)

Conservation status

New South Wales, Biodiversity Conservation Act 2016: Endangered.

Breeding season

The timing below describes a typical year based on the available information. Rainfall can extend breeding and increase captures outside the usual seasonal window.

The supplied documents do not provide a measured breeding chronology, young dependency period or monthly movement pattern for each state. Survey and clearing decisions should use local records, recent rainfall and habitat condition.

• Breeding: Breeding usually occurs from spring to early summer, or from late winter to early summer in the broader account. Breeding can occur at other times after favourable rainfall.
• Young: Litters may be present during and after the main breeding period. The duration of dependence is not reported, so the months shown are a practical representation of likely young presence rather than a measured dependency period.
• Movement and detectability: The species is highly transient or has a lifespan of less than two years at one monitored South Australian site. Capture rates increase after extended or above-average rainfall, which can occur in any month.
• Rainfall response: Population increases and higher capture rates have been recorded following extended or above-average rainfall. The timing therefore varies between sites and years.
• Highest clearing risk: Clearing during the main breeding and likely young-rearing period, from late winter through early summer, may affect adults, litters, burrows and food resources. Suitable habitat can also be occupied outside these months, especially after favourable rainfall.

Identification

Bolam's Mouse is a small, slender rodent that can resemble the introduced House Mouse and the Sandy Inland Mouse. Identification in the field should combine appearance, habitat, capture data and, where required, specialist examination.

The species weighs 9 to 21 g. Its head and body measures 50 to 80 mm and its tail measures 71 to 103 mm. The fur is dull amber-brown to olive-brown above, with dark hair tips, and white below. It has large eyes, relatively long ears, large hind feet and a long, heavily furred tail.

Identification: Distinguishing features

Bolam's Mouse is generally more slender than a House Mouse and has more prominent eyes, relatively longer ears and a longer tail. It lacks the musty odour commonly associated with House Mice. House Mice have a notch in the upper incisor, while Pseudomys species have two pairs of teats rather than the five pairs found in female House Mice.

It is externally similar to the Sandy Inland Mouse, Pseudomys hermannsburgensis, but Bolam's Mouse has longer hind feet and ears.

Identification: Field signs and handling

Animals are nocturnal and shelter in burrows. Burrows may be associated with rabbit warrens or abandoned goanna holes, so burrow entrances and recent disturbance around warrens can indicate potential habitat.

The supplied sources do not describe diagnostic tracks, scats, calls or eyeshine. Live trapping and expert examination may be needed where identification from photographs or external characters is uncertain.

Distribution: National range

Bolam's Mouse occurs in arid and semi-arid parts of southern Australia. Its distribution is patchy, and records in New South Wales are concentrated in the far south-west.

The species is found in southern Western Australia and South Australia, extending east into the south-western corner of New South Wales. It was collected in Victoria in 1857 but has not been recorded there since.

The supplied records include the Broken Hill Complex and Murray Darling Depression bioregions in New South Wales. Known or predicted subregions listed for New South Wales are Barrier Range, Barrier Range Outwash, Scopes Range and South Olary Plain.

• Treat records as indicative rather than continuous distribution, because the NSW profile states that mapped areas may contain only suitable parts of a subregion.

Distribution: Known strongholds and outlying records

In New South Wales, records are centred on the Scotia Mallee, including Tarawi Nature Reserve, Nanya Station, Scotia Sanctuary and surrounding properties. Additional records occur on leasehold land south-east of Mungo National Park.

Subfossil remains are known from Mutawintji National Park. Trapping east of Broken Hill extended the known NSW distribution and identified additional habitat, consistent with similar habitat in South Australia west of Broken Hill.

Distribution: Population information

The supplied documents do not provide a national population estimate, density, or quantified population trend. Low recapture rates at one South Australian site indicate that animals may be highly transient, or may live for less than two years.

Capture rates increase after above-average or extended rainfall. This suggests that detectability and local abundance can vary substantially between dry and wet periods.

National population estimate: Not reported in the supplied documents.

Population trend: Not quantified; local populations can increase after extended rainfall.

NSW status: Endangered.

Commonwealth status: Not listed.

Habitat: Vegetation communities

Bolam's Mouse uses a range of arid and semi-arid vegetation communities, with a preference for structurally varied shrub and ground layers. Habitat value is strongly associated with food plants, cover and relatively undisturbed soil.

Preferred habitat includes chenopod shrubland plains and low mallee woodland with a developed understorey of Acacia, Dodonaea or Eremophila species. The species has also been recorded in mallee and spinifex, mallee shrubland, Belah woodland, and mixed open shrubland or woodland.

It appears to favour plains, spillways and valley bottoms with loam or clay soils. Other published habitat descriptions include chenopod shrubland plains, low Acacia and Eucalyptus woodland, and Casuarina woodland.

Habitat: Structural features

Retain dense understorey, bluebush patches, spinifex, leaf litter, woody debris and connected native vegetation. These features provide food, shelter and protection from predators.

Mallee woodlands in the region can contain spinifex, shrubs, grasses, herbs, woody debris and leaf litter. The understorey varies with soil type, landform and fire history.

Habitat: Site limits

The supplied documents do not give an elevation range, minimum patch size or defined climatic boundary. They describe an arid and semi-arid distribution in southern Australia and an association with rainfall-driven increases in activity or capture rates.

Foraging habitat: Diet

Bolam's Mouse is an omnivorous, nocturnal forager. It feeds among shrub and ground layers and may forage in adjacent swales or across nearby patches of suitable cover.

The diet includes seeds, fruits, blossoms, grasses and herbs, together with invertebrates such as beetles and spiders. A published dietary summary reports plant material, including leaves, flowers, stems and roots, as about 30 percent, invertebrates as about 10 percent and fungi as about 1 percent, with the balance and composition varying with season and food availability.

Food plants noted in the NSW profile: Bluebush, Maireana species, together with grasses, herbs, Acacia, Dodonaea and Eremophila resources.

Animal prey noted: Beetles, spiders and other invertebrates.

Foraging habitat: Foraging places

Capture rates are higher where bluebush, Maireana species, has high cover, and bluebush seeds have been recorded as a food source. The species often forages in adjacent swales and favours plains, spillways and valley bottoms where suitable soils and vegetation occur.

No measured foraging range or home range is provided in the supplied documents. Males are reported to move more than females.

• Retain bluebush patches, native ground cover, spinifex and adjoining swales when planning access tracks, work areas and clearing boundaries.

Breeding habitat: Breeding biology

Breeding is linked mainly to late winter, spring and early summer, but favourable rainfall can allow breeding at other times. Breeding habitat is likely to be most suitable where food plants, dense cover and nearby burrows remain available.

Breeding usually occurs in spring and early summer, or from late winter to early summer in the broader published account. Breeding can occur at other times after favourable rainfall. Litters have a maximum of six young, with four reported as usual in one source.

Breeding season: Usually late winter, spring and early summer, with breeding possible at other times after favourable rainfall.

Litter size: Usually four in one published account; maximum six in the NSW profile.

Gestation: Not reported in the supplied documents.

Age at maturity: Not reported in the supplied documents.

Lifespan: Less than two years or highly transient, based on low recapture rates at one South Australian site.

Breeding habitat: Breeding habitat

Suitable breeding areas include chenopod shrubland plains and low mallee woodland with Acacia, Dodonaea or Eremophila understorey. Burrows provide shelter, and may occur in sandy soils, old rabbit warrens or abandoned goanna holes.

Avoid removing connected shrub cover, spinifex, bluebush and burrow habitat during the main breeding period. The supplied documents do not identify a separate nesting structure or breeding territory size.

Sheltering habitat: Burrows and warrens

Bolam's Mouse shelters below ground and uses dense vegetation and ground cover for protection. Existing burrows and cover should be treated as potential fauna habitat during site preparation.

The species uses burrows for shelter. Burrows may be in sandy soils and can be associated with old rabbit warrens or abandoned goanna holes.

The supplied documents do not provide burrow dimensions, depth, entrance diameter or whether the species excavates its own burrows.

• Inspect rabbit warrens, goanna holes and other burrow systems before clearing or earthworks in suitable habitat.
• Avoid filling, ripping or collapsing burrows where the species may occur, and retain nearby vegetation that provides cover around entrances.

Sheltering habitat: Above-ground cover

Dense Acacia, Dodonaea, Eremophila and chenopod understorey, bluebush, spinifex, leaf litter and woody debris can provide cover between burrows and feeding areas. Maintaining these features also retains shelter and food resources after rainfall.

The species is nocturnal, so disturbance and inspection timing should account for animals leaving or returning to shelter at night.

Threats: Clearing and fragmentation

The main documented pressures are habitat loss and degradation, introduced predators, grazing and competition for food and shelter. Small and isolated populations may be especially sensitive to fire, drought-related resource loss and post-fire predation.

Historical and current land use have reduced and isolated habitat in parts of the NSW range. Clearing chenopod shrubland, mallee understorey, spinifex, bluebush patches, burrows or adjoining swales can remove feeding and shelter resources.

Fragmentation can reduce movement between populations and leave small habitat patches more exposed to wildfire, overgrazing, resource loss and predation.

• Minimise clearing of foraging habitat, shelter and food plants, particularly areas with bluebush species.
• Retain connected native vegetation around known records and suitable habitat patches.

Threats: Fire and grazing

Fire regimes that are too frequent can remove habitat structure and food resources. Large wildfires may affect small and isolated populations, particularly when shelter and food are lost at the same time.

Domestic stock, feral goats, rabbits and other introduced herbivores can reduce understorey condition, food availability and shelter. Trampling and burrowing can also alter soil structure and increase erosion.

• Avoid burning all suitable habitat within a region at one time.
• Reduce grazing intensity or exclude grazing in areas where vegetation regeneration and ground cover are needed.

Threats: Predators and competitors

Foxes and feral cats prey on Bolam's Mouse. Predation may be particularly important during population declines or after fire, although its extent in New South Wales is not well quantified.

Introduced house mice can compete for food, especially near agricultural crops and in some large reserves. Stock, rabbits and goats also compete for food and habitat resources.

• Include fox, feral cat and rabbit control in site management where appropriate and lawful.
• Assess house mouse activity near crops or disturbed areas when evaluating competition risk.

Threats: Other pressures and information gaps

The supplied documents identify uncertainty about climate change effects on food availability, fire regimes, predation and habitat suitability. They also identify limited knowledge of climate refuges, distribution during low-abundance periods and the extent of predation.

Road impacts, disease and hydrology change are not identified as specific threats in the supplied documents. Project assessments should still record any direct disturbance, vehicle access, drainage alteration or disease observations rather than assuming these pressures are absent.

Survey methodology: 1. Nocturnal searches

No species-specific survey guideline was supplied in the documents. Survey design should therefore be set by a suitably qualified ecologist, with emphasis on nocturnal detection, chenopod and mallee habitat, and periods after favourable rainfall.

Conduct targeted nocturnal searches because Bolam’s Mouse is nocturnal and uses burrows for shelter.

Search chenopod shrubland plains, low mallee woodland, valley bottoms, spillways and areas with bluebush, Acacia, Dodonaea, Eremophila or spinifex understorey.

Give priority to loam or clay soils, sandy soils with burrows, abandoned rabbit warrens and old goanna holes.

Time searches for spring and early summer, and repeat them after above-average rainfall because capture rates and population size can increase after extended rain.

Record weather, rainfall history, start and finish times, search area, habitat condition, burrow locations and all observations.

Activity period: Nocturnal

Breeding period: Usually spring and early summer, with breeding possible at other times after favourable rainfall

Adult size: Head and body 50 to 80 mm, tail 71 to 103 mm, weight 9 to 21 g

Survey methodology: 2. Live trapping and targeted habitat checks

Use an approved live-trapping program where nocturnal searches cannot establish presence or absence and the level of impact warrants trapping.

Obtain the required animal ethics, wildlife handling and land access approvals before trapping, and use experienced personnel trained to identify and handle small native rodents.

Place traps around chenopod shrubland, mallee understorey, bluebush, swales, valley bottoms, burrows and abandoned rabbit warrens, using a design that samples the full impact area and nearby retained habitat.

Do not treat a failed trapping session as evidence of absence because long-term monitoring has recorded low recapture rates and the species may be highly transient or have a lifespan of less than two years.

Record trap locations, trap nights, weather, rainfall, habitat, captures, non-target animals and any evidence of house mice or other introduced competitors.

Survey methodology: 3. Identification and detection records

Confirm suspected records from photographs or examination by a competent mammal ecologist because Bolam’s Mouse resembles the House Mouse and the Sandy Inland Mouse.

Check for the species’ more prominent eyes, relatively longer ears and tail, slender form, lack of a musty odour and the absence of the House Mouse upper-incisor notch.

Record the exact location, date, observer, identification features, photographs, habitat type, soil type, understorey condition and nearby disturbance.

Map known or predicted habitat and all burrows or warrens that could be affected by clearing, access tracks, trenching or machinery movement.

Key distinguishing features: Large eyes, relatively long ears and tail, slender body, no musty odour, and no upper-incisor notch

Relevant NSW areas: Scotia Mallee, including Tarawi Nature Reserve, Nanya Station, Scotia Sanctuary and surrounding properties, with additional records near Mungo National Park and east of Broken Hill

Survey methodology: Minimum effort and reporting

• Set the survey effort, number of nights, trapping effort, search hours and survey area in a written, impact-based survey plan because the supplied documents do not specify a minimum effort.
• Survey when animals are most likely to be detectable, including nocturnal periods and suitable periods following above-average rainfall, and document any dry, hot, windy or otherwise poor conditions that reduce detection.
• Have a qualified ecologist review negative results against habitat quality, rainfall, survey conditions and the species’ potentially transient occurrence before clearing is approved.
• Submit confirmed records and suitable negative-survey information to the relevant state wildlife database; for NSW, use the Atlas of NSW Wildlife or the current NSW biodiversity recording system.
• Report records to the project environmental officer, regulator and land manager, and retain raw field data, photographs, trap sheets, maps and animal handling records.

Before habitat disturbance: Avoid and minimise

Treat suitable chenopod and mallee habitat as potential Bolam’s Mouse habitat even when the species has not been detected. The species is endangered in NSW, while it is not listed under the EPBC Act in the supplied information.

• Avoid clearing chenopod shrubland plains, low mallee woodland, bluebush patches, spinifex, developed shrub understorey, valley bottoms and spillways where practicable.
• Retain connected areas of suitable habitat rather than leaving small isolated patches, because historical and current land use have contributed to habitat loss and isolation.
• Retain woody debris, leaf litter, dense understorey, burrows, abandoned rabbit warrens and old goanna holes that can provide shelter.
• Avoid removing bluebush and other food plants, particularly Maireana species, because bluebush seed has been recorded as a food source.
• Keep grazing, vehicle access, soil disturbance and machinery laydown outside retained habitat wherever practicable.

Before habitat disturbance: Approvals and project planning

NSW status: Endangered

Commonwealth status in the supplied profile: Not listed

• Confirm the applicable state or territory threatened-species requirements before work starts, noting that Bolam’s Mouse is listed as Endangered in NSW.
• Check the current EPBC Act list and complete an EPBC referral assessment if the species becomes nationally listed or if another nationally protected matter may be affected; the supplied information records it as not listed under the EPBC Act.
• Obtain any required scientific, wildlife handling, trapping, animal ethics, clearing and rehabilitation approvals before survey, capture or disturbance.
• Prepare a fauna management plan that identifies habitat, survey results, no-go areas, clearing limits, fauna handling roles, stop-work triggers, reporting pathways and rehabilitation commitments.
• Stage clearing so that retained habitat remains connected and available while disturbed areas are progressively restored.

Before habitat disturbance: Site preparation

• Complete the approved pre-clearance survey during suitable nocturnal and post-rainfall conditions where practicable.
• Mark retained habitat, no-go areas, burrows, rabbit warrens, dense shrub patches, bluebush, spinifex and woody debris before machinery enters the site.
• Install exclusion fencing where it can keep machinery, people and stock out of retained habitat without blocking animal movement between habitat patches.
• Brief the fauna spotter catcher, operators and supervisors on identification features, handling limits, search areas, stop-work triggers and incident recording.
• Control or exclude stock, goats and rabbits from retained habitat where this is part of the approved project controls.

During habitat disturbance: Daily controls and clearing sequence

Use a controlled clearing sequence that keeps the fauna spotter catcher in direct contact with the machinery operator and supervisor. Stop work when a Bolam’s Mouse, a suspected individual, or an occupied shelter is found.

• Inspect exclusion fencing, no-go markers, access routes and retained habitat at the start of each work day.
• Clear in stages towards retained habitat where practicable, using slow machinery movement and allowing animals to move away from the active work area.
• Keep the fauna spotter catcher close enough to inspect ground cover, burrows, warrens, logs and dense shrubs before and during each clearing movement.
• Do not use fire, broad-scale grading or unnecessary ripping to flush animals from habitat.
• Suspend work during conditions that prevent effective observation, including poor visibility, excessive dust or unsafe weather, and record the reason.

During habitat disturbance: Habitat features and animal handling

Shelter types recorded for the species: Burrows, sometimes associated with rabbit warrens and abandoned goanna holes

Food plants and cover to protect: Bluebush, Acacia, Dodonaea, Eremophila, spinifex, grasses, herbs and woody debris

• Treat burrows, abandoned rabbit warrens, old goanna holes, dense bluebush, spinifex, logs and woody debris as potential shelter until checked by the fauna spotter catcher.
• Do not place hands into burrows or holes, and do not destroy or block a shelter during inspection.
• If a Bolam’s Mouse is found, stop machinery nearby and keep people, vehicles and dogs away from the animal.
• Allow the animal to leave under its own direction where safe, or have it captured and handled only by a person authorised under the project approvals.
• Relocate a captured animal only to nearby suitable retained habitat that is outside the work area and connected to existing cover, unless the approved wildlife procedure requires another location.
• Use suitable ventilated containers, minimise handling and heat exposure, and do not keep the animal longer than necessary.
• Take injured animals to an appropriately experienced veterinarian or authorised wildlife carer, following the project’s wildlife incident procedure.

During habitat disturbance: Stop work and records

• Stop work within the affected area when a Bolam’s Mouse or suspected Bolam’s Mouse is sighted, captured, injured or killed.
• Stop work if an occupied burrow, warren or shelter cannot be safely assessed before disturbance.
• Notify the fauna spotter catcher, site supervisor and environmental officer, and obtain approval before restarting work in the affected area.
• Record the date, time, exact location, activity, habitat, animal condition, photographs, identification basis, handler, action taken, release location and restart approval.
• Record all injuries, deaths, escapes, unauthorised clearing and breaches of exclusion fencing as environmental incidents.
• Submit confirmed records to the relevant state wildlife database and update the project map and fauna register.

After habitat disturbance: Post-clearance checks

Post-clearance checks should confirm that no animal or shelter has been left within the work footprint and that retained habitat controls remain effective. Use the results to adjust work methods and rehabilitation.

• Inspect the cleared footprint, retained edges, access tracks, spoil areas and disturbed burrows after each clearing stage.
• Check for live animals, carcasses, tracks, burrow entrances, displaced logs, damaged exclusion fencing and newly isolated habitat patches.
• Have a qualified ecologist review any new record or suspected record before further disturbance proceeds.
• Repair damaged fencing and reinstate no-go markers immediately where retained habitat could be entered by machinery or stock.
• Update the fauna register, spatial data, incident records and clearing completion maps.

After habitat disturbance: Monitoring and reporting

• Monitor retained habitat and relocation areas using the approved project method, with attention to nocturnal activity and periods following favourable rainfall.
• Compare monitoring results with pre-clearance records, habitat condition and the location of nearby disturbance rather than relying only on whether an animal is detected.
• Report monitoring results, injuries, deaths, relocations, habitat loss and control failures to the regulator and land manager where required by approval conditions.
• Maintain predator, grazing, rabbit and weed controls that are required to protect retained or rehabilitated habitat.
• Apply any approved offset or compensatory habitat measure where impacts cannot be avoided or minimised, and document its location, condition and management obligations.

Rehabilitation actions: Rebuild habitat structure

Rehabilitation should rebuild the shelter, food resources and understorey used by Bolam’s Mouse. Prioritise habitat that links retained mallee and chenopod areas and remains suitable during periods of low rainfall.

• Re-establish local chenopod shrubland and low mallee woodland communities using locally appropriate native species and seed sources.
• Include bluebush, Acacia, Dodonaea and Eremophila species where they match the pre-disturbance community and approved rehabilitation design.
• Reinstate spinifex, grasses, herbs, leaf litter and woody debris to provide cover and foraging habitat.
• Retain or replace suitable logs and other ground cover, and do not remove fallen timber from rehabilitation areas without an ecological reason.
• Restore soil profiles, drainage and compacted areas so that burrows and understorey vegetation can develop.

Rehabilitation actions: Manage threats

• Control foxes, feral cats and rabbits in accordance with approved pest management requirements.
• Manage goats, domestic stock and other introduced herbivores so that shrubs, ground cover and food plants can regenerate.
• Prevent house mice from gaining access to food stores, buildings and disturbed areas where practicable, particularly near agricultural crops or other high-risk sites.
• Use a fire regime that does not burn all suitable habitat and food resources in one event, and supports natural vegetation succession.
• Control weeds and prevent new tracks, vehicle access and stock access from degrading rehabilitated areas.

Rehabilitation actions: Success measures and monitoring

• Set rehabilitation success measures for native shrub cover, bluebush and spinifex persistence, woody debris, soil stability, absence of damaging grazing and connectivity with retained habitat.
• Inspect rehabilitation after establishment, after major rainfall and after fire to identify erosion, grazing, weed invasion, pest activity and loss of shelter.
• Use repeat nocturnal searches or approved trapping in suitable seasons and after favourable rainfall to assess whether Bolam’s Mouse returns to rehabilitated or retained habitat.
• Continue monitoring until the approved success criteria are met and record methods, effort, weather, rainfall, detections and management actions.
• Submit confirmed records and relevant monitoring data to the appropriate state wildlife database.

Sources

• Bolam's Mouse - profile, NSW Department of Climate Change, Energy, the Environment and Water: https://threatenedspecies.bionet.nsw.gov.au/profile?id=10684
• Pseudomys bolami - Zenodo, zenodo.org: https://zenodo.org/records/6868542
• [PDF] Threatened species of far south-western NSW, NSW Department of Climate Change, Energy, the Environment and Water: https://www.environment.nsw.gov.au/sites/default/files/threatened-species-far-south-western-nsw-190271.pdf