Arnhem Phasmid Gecko (Strophurus horneri)

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

Breeding season

Species-specific breeding timing is not recorded for the Arnhem Phasmid Gecko. Genus-level information indicates breeding and egg laying from September to February, with eggs incubating for about 45 to 80 days. Plan clearing controls across this period and retain spinifex clumps and nearby sandstone shelter throughout the year.

Reproductive mode: Oviparous, meaning females lay eggs.

Clutch size: Two eggs per clutch.

Incubation: 45 to 80 days at genus level; species-specific incubation is not recorded.

Size at hatching: Not recorded.

Age at maturity: About 2 to 3 years at genus level; species-specific maturity is not recorded.

Nest or egg sites: Not recorded for this species. Genus-level information lists sites under rocks, at the base of trees and in abandoned animal burrows. This species has been recorded in dense spinifex associated with sandstone escarpments and boulders.

Breeding frequency: Not recorded.

Confirm timing locally before works, using local rainfall and temperature patterns because these may influence activity, breeding and egg laying in this tropical species.

• Mating: Species-specific mating months are not recorded. Genus-level information places the breeding season from September to February, so mating may occur during this period.
• Gravid females: Species-specific records of gravid females are not available. Females carrying two eggs are reported at genus level, with the breeding period extending from September to February.
• Egg laying: The species is reported to lay two eggs per clutch, but its laying months are not recorded directly. Genus-level information gives September to February for the breeding season.
• Incubation: Eggs are reported to incubate for 45 to 80 days at genus level. Applying that duration to the September to February laying period gives a possible incubation window from September to April, but the timing is not confirmed for this species.
• Hatchlings: Species-specific emergence months are not recorded. A 45 to 80 day incubation following September to February laying suggests that hatchlings may emerge from November to April.
• Active period: The species is nocturnal, and one individual was captured at night in a spinifex clump. Treat it as potentially surface active in every month during suitable night conditions; seasonal activity peaks are not recorded.
• Highest clearing risk: Clearing risk applies year round because dense spinifex and sandstone shelter may be occupied, and no species-specific inactivity period is recorded. Risk may be greater from September to April when genus-level breeding, egg laying, incubation and hatchling emergence may overlap.

Identification

This is a small, slender, spinifex-associated gecko that can be difficult to detect in dense hummock grass. Its striped appearance and stick-insect-like proportions are useful when animals are found at night in spinifex.

The Arnhem Phasmid Gecko has a very small, slender body, with a recorded snout to vent length of 35.7 mm and a diagnosis of about 36 mm. The head is wider than the body and flattened, with large eyes, a vertical pupil and a rounded snout. The original tail is shorter and narrower than the body, distinctly inflated around the middle, and can be prehensile.

Live animals have four broad yellow longitudinal stripes over a greyish or brown background. The venter is relatively plain, with small brown flecks or, at most, a single thin longitudinal stripe. The species has no caudal spines or tubercles.

Recorded snout to vent length: 35.7 mm for the holotype; diagnosis approximately 36 mm.

Diagnostic supralabials: Usually 13 to 15 relatively small supralabials.

Tail: Inflated around the midpoint, shorter than the body in the holotype, and without caudal spines or tubercles.

• Look for a very small gecko with a narrow, slender body and a disproportionately broad, flattened head.
• Check for four broad yellow stripes running lengthwise along the back and tail when the animal is viewed alive.
• Record the habitat clump or rock feature where the animal was found, because the species is associated with spinifex near sandstone.

Identification: Distinguishing similar geckos

The most geographically proximate similar species is the Phasmid Striped Gecko, Strophurus taeniatus. The Arnhem Phasmid Gecko has smaller and more numerous supralabials, four broad yellow stripes and a relatively plain underside. Strophurus taeniatus usually has three wide brown stripes, thinner yellow stripes and more continuous thin striping on the underside.

It is smaller and more slender than Strophurus mcmillani and Strophurus robinsoni. It differs from several other spinifex-associated Strophurus by having an internasal scale separating the rostral scale from the nostril.

Comparison with Strophurus taeniatus: Arnhem Phasmid Gecko: 13 to 15 supralabials and four broad yellow stripes; Strophurus taeniatus: usually 10 to 12 supralabials, three broad brown stripes and thinner yellow stripes.

Comparison with Strophurus mcmillani: Arnhem Phasmid Gecko about 36 mm snout to vent length, compared with 40.3 to 49.1 mm for Strophurus mcmillani.

Comparison with Strophurus robinsoni: Arnhem Phasmid Gecko about 36 mm snout to vent length, compared with 53.0 to 56.0 mm for Strophurus robinsoni.

• Do not identify the species from preserved colour alone, because the yellow pigmentation is not apparent in preservative.
• Use photographs of the live animal where possible, together with locality, habitat, size and scale characters.
• Treat specimens from the southern and central Arnhem Plateau cautiously, because the original authors recorded possible morphological variation and unresolved populations identified as Strophurus cf. horneri.

Identification: Sexes and field signs

The holotype was female. The authors presumed that males lack post-cloacal or femoral pores, as in related taxa, but stated that this character had not been confirmed for the species.

No species-specific information is provided on tracks, scats, calls, nests, sloughs or eyeshine. A live individual, a photograph or a safely collected voucher is therefore more useful than indirect signs for confirmation.

• Do not rely on pores alone to sex an animal in the field until the character is confirmed for this species.
• Photograph the dorsal pattern, head and tail, and document the exact spinifex and sandstone setting.
• Avoid removing animals from spinifex unless collection is authorised and necessary for identification.

Distribution: National range

The species is known only from the Arnhem Plateau region in the Top End of the Northern Territory. The available records are sparse, and the full extent of the range and the boundaries between Arnhem Plateau populations remain unresolved.

All documented records are from the Northern Territory. The type locality is Yirrkakak on the northern edge of the Arnhem Plateau. Other observations and genetic material come from localities along the western edge of the plateau, including southern Kakadu National Park, Namarragon Gorge and other Kakadu localities.

The species may occur across the western and northern Arnhem Plateau, but this has not been confirmed. No records are provided from Queensland, Western Australia or any other Australian state or territory.

State or territory: Northern Territory only in the supplied records.

Bioregional setting: Arnhem Plateau region, including Kakadu National Park and the western and northern plateau margins.

Known strongholds: No population stronghold has been established. Records include Yirrkakak, southern Kakadu, Namarragon Gorge and other western Arnhem Plateau localities.

Population size: Not known.

Population trend: Not known.

Survey record: The original description was based on very few specimens and noted that the total number of available specimens remained very small.

• For project screening, treat the Arnhem Plateau and adjacent western and northern Arnhem Land sandstone country as potential habitat until a suitably timed survey excludes the species.
• Do not extend the known distribution to other states or territories on the basis of records for the similar Strophurus taeniatus.

Distribution: Subpopulations and uncertainty

Genetic divergence between two northern Arnhem Plateau samples was high, at 8.8 percent, and additional specimens from the southern and central plateau showed possible morphological differences. Further material and genetic data are needed to resolve whether these represent separate populations or additional taxa.

The species is listed as Vulnerable in the supplied Queensland Government table, although that table is not a distribution assessment and does not provide a population estimate.

• Record the location of every detection at a scale that allows separate sandstone outcrops, gullies and spinifex patches to be mapped.
• Seek specialist identification for animals from the southern or central plateau that do not match the typical four-stripe pattern.

Habitat: Habitat setting

The Arnhem Phasmid Gecko is associated with the rugged sandstone country of the Arnhem Plateau and with mature spinifex structure. The available evidence points to a narrow combination of rocky shelter and well-developed hummock grass cover.

Known animals were found in well-developed spinifex patches on or at the base of large sandstone escarpments or boulders. One animal was found in a spinifex clump at Namarragon Gorge, and another was comparatively easy to find in long-unburnt spinifex in a sheltered gully in southern Kakadu.

The Arnhem Plateau is a deeply dissected sandstone region with escarpments generally 100 to 400 metres above sea level. This elevation range describes the regional plateau setting and is not a confirmed species-specific limit.

Primary vegetation: Well-developed spinifex, including Triodia hummock grass clumps.

Rock structure: Large sandstone escarpments and boulders, including their bases.

Recorded microhabitat: A sheltered gully containing long-unburnt spinifex.

Regional elevation: The Arnhem Plateau is generally 100 to 400 metres above sea level; a species-specific elevation range is not available.

• Map spinifex hummocks, sandstone outcrops, boulder bases, escarpment footslopes, gullies and areas with long-unburnt grass cover.
• Retain connected spinifex patches around rocky features rather than clearing only the visible rock face.
• Treat sheltered gullies with mature spinifex as higher-priority habitat for avoidance and targeted survey.

Habitat: Structural features

The important structural combination appears to be dense, established spinifex close to sandstone shelter. The striped pattern provides camouflage in this setting.

The supplied documents do not define a minimum spinifex patch size, required rock dimensions, canopy cover or hydrological condition.

• Before clearing, inspect the full margin of rocky outcrops and boulders, including spinifex clumps at their bases.
• Avoid breaking up long-unburnt spinifex patches with access tracks, stockpiles or temporary work areas.
• Where disturbance cannot be avoided, retain spinifex cover and rocky shelter between work areas and maintain links between occupied patches.

Foraging habitat: Known information

Species-specific diet, prey, feeding rates and foraging distances have not been reported in the supplied documents. Field management should therefore focus on retaining the spinifex and rocky structure where feeding is likely to occur.

The species is a small climbing gecko in a genus that includes spinifex-associated taxa. The available records place it within spinifex clumps on or near sandstone features, including a confirmed night-time capture in a spinifex clump.

The documents do not identify prey species, key food plants, daily foraging distance, home range or feeding height.

Diet: Not reported in the supplied documents.

Foraging range: Not reported in the supplied documents.

Recorded feeding habitat: Not directly documented; the species has been recorded at night in a spinifex clump.

• Survey and manage the entire spinifex clump and adjacent rock structure as potential foraging habitat.
• Avoid removing scattered spinifex tussocks around occupied rocky features simply because no animal is visible during daylight searches.
• Record the time, weather, spinifex condition and exact position of each observation to improve knowledge of foraging activity.

Breeding habitat: Breeding information

Breeding behaviour and reproductive timing are not described in the supplied documents. The habitat information supports retaining mature spinifex and nearby sandstone shelter until breeding sites are better understood.

No information is available on mating, egg laying, clutch size, incubation, hatching, maturity, lifespan or nest sites for Strophurus horneri.

There is no evidence in the supplied documents for a particular breeding season or for use of tree hollows, burrows or other defined nest structures.

Breeding season: Unknown.

Clutch size: Unknown.

Gestation or incubation: Unknown.

Age at maturity: Unknown.

Lifespan: Unknown.

Known breeding habitat: Not specifically documented; mature spinifex near sandstone shelter should be retained as potential breeding habitat.

• Do not assume that the absence of a visible nest means that a spinifex patch is not being used for breeding.
• Retain dense spinifex and adjacent sandstone refuges during project planning because these are the only documented habitat features associated with the species.

Sheltering habitat: Documented refuge setting

The species has been found in spinifex clumps associated with sandstone escarpments and boulders. Specific refuge dimensions and whether animals use rock crevices, the interior of hummocks or other shelters have not been documented.

A specimen at Namarragon Gorge was captured at night in a spinifex clump. Other records were from well-developed spinifex on or at the base of large sandstone escarpments or boulders.

The species has no documented dependence on tree hollows, soil burrows, caves or constructed refuges. Its slender body, climbing gecko form and prehensile tail are consistent with use of dense grass and rocky structure, but the precise refuge behaviour remains untested.

Documented refuge: Spinifex clumps.

Associated shelter: Large sandstone escarpments and boulders, including their bases.

Refuge size: Not reported.

Other refuge types: Tree hollows, burrows, caves and crevices have not been confirmed in the supplied documents.

• Retain dense spinifex hummocks, especially where they touch or overlie sandstone and boulder margins.
• Keep machinery, spoil, fuel and materials out of spinifex clumps and rock crevices near work areas.
• Use hand searches and careful night inspection around spinifex and rock bases where disturbance is unavoidable, under the relevant permit and animal welfare requirements.

Threats: Fire

The most clearly documented threat in the supplied material is inappropriate fire. Direct clearing and construction can remove the small, specialised habitat patches on which the species depends, while introduced predators, herbivores and plants may add pressure.

The original species account identifies fire frequency as a factor that may shape the distribution and abundance of the Arnhem Phasmid Gecko. It also reports that cessation of traditional Aboriginal burning practices has been associated with increases in fire frequency and intensity across the Arnhem Plateau.

Long-unburnt spinifex in a sheltered gully supported a comparatively easy detection, but this observation does not establish that all long-unburnt areas are suitable or that frequent burning is safe.

• Do not burn occupied or potential spinifex habitat without a species-specific fire assessment and appropriate approvals.
• Retain unburnt refuge patches around sandstone outcrops and maintain a range of spinifex ages across the site.
• Record fire history, burn extent, season and intensity during pre-clearance surveys.

Threats: Clearing and construction

Clearing can directly remove spinifex hummocks and the sandstone or boulder-edge structure used by the species. Fragmenting the small number of known habitat patches may also make local populations harder to detect and manage.

The supplied documents do not quantify the species response to roads, traffic, vibration, dust, artificial light, hydrology change or construction noise.

• Avoid clearing dense spinifex on or below sandstone escarpments and around boulders wherever practicable.
• Keep access tracks, laydown areas, drainage works and spoil placement outside mapped spinifex and rocky refuge patches.
• Use a qualified fauna spotter catcher and an approved relocation or rescue procedure if animals are exposed during works.

Threats: Introduced species and other pressures

The regional discussion identifies introduced predators, herbivores and plants as possible significant pressures on Arnhem Plateau biodiversity. Their effects on Strophurus horneri have not been measured directly.

No species-specific disease threat is reported in the supplied documents.

• Prevent construction materials, vehicles and equipment from spreading introduced plants into spinifex and sandstone habitat.
• Manage weeds and feral herbivore access where they reduce spinifex cover or alter fuel structure.
• Apply hygiene procedures between sites even though a disease has not been recorded for this species.

Survey methodology: 1. Habitat assessment and transects

Use targeted nocturnal searches in spinifex growing on or beside sandstone escarpments and boulders. The available sources do not provide a species specific survey guideline or prescribed effort, so the project ecologist must set and justify effort from the area of suitable habitat, disturbance footprint and survey limitations.

Map well developed spinifex patches on sandstone escarpments, boulder bases and sheltered gullies before selecting survey areas.

Prioritise long unburnt spinifex because the species was reported as comparatively easy to find there, and record recent fire history where it is available.

Walk systematic transects through all suitable patches, including habitat within and beside the proposed disturbance footprint, and record transect length, width, start and finish times, weather, fire history and habitat condition.

Survey methodology: 2. Nocturnal spotlighting

Spotlight spinifex clumps and the faces, ledges and bases of sandstone escarpments and boulders after dark, when the gecko is likely to be active and visible.

Search slowly and inspect the outer stems and interior of each spinifex clump, as the species uses spinifex and its striped pattern provides camouflage in that habitat.

Record each observation with a location, time, searcher name, search duration, weather, habitat description and whether the animal was seen on or beside spinifex.

Survey methodology: 3. Targeted clump searches

Undertake careful active searches of suitable spinifex clumps during the night, using a torch and avoiding damage to occupied clumps.

Inspect spinifex at the base of large sandstone features and in sheltered gullies, which are documented habitat settings for the species.

Do not rely on a single visit or a single occupied clump as evidence that nearby suitable habitat is unoccupied, because the species is small, secretive and difficult to detect.

Survey methodology: Minimum effort and reporting

• Define the survey area, suitable habitat area, transect coverage, number of observers, search hours and number of visits before fieldwork starts.
• Repeat searches where access, weather, recent fire or dense spinifex limits detection, and explain any departures from the planned effort in the report.
• Report all records, including records from outside the impact area, to the relevant state or territory wildlife database and retain coordinates, photographs and voucher information where collection is lawful.
• Submit records and survey results to the project approvals system and the Australian Government where required by the EPBC approval or referral conditions.

Before habitat disturbance: Avoid and minimise

Treat spinifex on sandstone country as potential habitat wherever it occurs in the Arnhem Plateau region. The species is nationally listed as Vulnerable, so confirm approval and permit requirements before any clearing or habitat disturbance.

• Retain well developed spinifex patches on or at the base of sandstone escarpments and boulders, especially in sheltered gullies and long unburnt areas.
• Keep connected areas of suitable spinifex and sandstone habitat between retained patches, rather than creating isolated remnants around the work area.
• Minimise the disturbance footprint, vehicle access, night lighting and soil or rock disturbance around retained spinifex clumps.
• Design the works to retain the sandstone features and boulder bases used by the species, not only the vegetation cover.

Before habitat disturbance: Approvals and planning

EPBC status: Vulnerable

Documented distribution: Arnhem Plateau region in the Top End of the Northern Territory

Documented habitat: Well developed spinifex on or at the base of sandstone escarpments or boulders

• Check whether the proposed action requires an EPBC Act referral or approval because the Arnhem Phasmid Gecko is nationally listed as Vulnerable.
• Check state or territory wildlife legislation, collection requirements and fauna handling permits before surveys, capture or relocation.
• Prepare a fauna management plan that identifies suitable habitat, survey effort, no-go areas, authorised handlers, stop-work triggers, release sites, injury response and reporting requirements.
• Stage clearing so that retained habitat is protected before machinery enters the site and so that the spotter catcher can inspect each work area.

Before habitat disturbance: Site preparation

• Complete a targeted pre-clearance survey of all suitable spinifex and sandstone habitat within the disturbance footprint and along access routes.
• Mark retained spinifex, sandstone features, boulder bases and connected habitat on plans and on the ground before clearing begins.
• Install exclusion fencing or other clearly visible barriers where they can protect retained spinifex and prevent machinery entry.
• Brief operators on the species, its small size, nocturnal activity, camouflage and the requirement to stop when directed by the fauna spotter catcher.

During habitat disturbance: Daily clearance controls

The fauna spotter catcher must control the clearance sequence in suitable habitat and must have authority to stop machinery. Work should proceed in small, inspected stages, with all observations and animal movements recorded.

• Inspect the work area, exclusion fencing, retained spinifex and sandstone features at the start of each day.
• Clear only the area inspected and released by the fauna spotter catcher, and keep machinery outside marked habitat and no-go areas.
• Use a slow, staged clearance sequence that allows the spotter catcher to inspect spinifex clumps and ground around boulders before and during disturbance.
• Stop work immediately if the fauna spotter catcher cannot maintain visual control of the active clearance area or if an animal is detected.

During habitat disturbance: Animal handling and relocation

• Do not allow untrained workers to handle the gecko, and use only personnel authorised under the relevant wildlife permit or approval.
• If the gecko is found, stop machinery, secure the immediate area and allow the authorised spotter catcher to capture or direct the response.
• Relocate a healthy animal only to nearby retained habitat that contains suitable spinifex and sandstone cover, and record the release location and time.
• Keep handling time as short as practicable, prevent crushing or overheating, and do not move the animal to an unapproved distant site.
• Send an injured animal to an appropriately qualified veterinarian or licensed wildlife carer under the project fauna management plan.

During habitat disturbance: Habitat feature controls

• Inspect each spinifex clump before removal and check the ground, rock edges and sheltered spaces around sandstone escarpments and boulders.
• Do not remove or disturb retained sandstone features, boulders or spinifex unless they are within the approved footprint and have been cleared by the spotter catcher.
• Treat logs, loose rocks and dense ground cover near spinifex as potential refuge until inspected, even though the available species account does not identify them as confirmed shelter features.
• Do not burn, chip or bury removed habitat material until the fauna inspection and any approved relocation process are complete.

During habitat disturbance: Stop-work triggers and records

• Stop work for any confirmed Arnhem Phasmid Gecko record, any suspected record that requires identification, or any animal injured during clearance.
• Stop work if exclusion fencing fails, suitable habitat is found outside the surveyed area, or clearing extends beyond the approved footprint.
• Record the date, time, exact location, habitat, animal condition, photographs, handler, action taken, release site and approval or permit reference for every encounter.
• Report mortality, injury, unapproved clearing and unsuccessful relocation through the approval and incident reporting process.

After habitat disturbance: Post-clearance checks

Post-clearance work should confirm that no animals remain in the disturbed area, protect retained habitat and test whether mitigation is working. The species account identifies fire frequency and habitat condition as management issues, so retain these records for future review.

• Inspect the cleared footprint, retained spinifex edges and sandstone features after each clearance stage for surviving, injured or trapped animals.
• Complete a final check before demobilisation and record the area checked, observers, time, weather and any animal findings.
• Repair exclusion fencing and close access points that could allow machinery or people to enter retained habitat.

After habitat disturbance: Monitoring and reporting

• Monitor retained spinifex and sandstone habitat using the same nocturnal search approach used for the pre-clearance survey so that results can be compared.
• Record changes in spinifex cover, fire history, weed invasion, erosion, unauthorised access and predator activity around retained patches.
• Provide survey records, incidents, relocations, mortality, monitoring results and photographs to the approval authority and relevant state or territory wildlife database.
• Review mitigation if monitoring shows loss of spinifex, repeated animal displacement, isolation of retained patches or increased fire frequency.

After habitat disturbance: Offsets and residual impacts

• Determine whether an offset or additional conservation measure is required under the EPBC approval, referral decision or state approval conditions.
• Base any offset or residual impact assessment on the confirmed area and condition of Arnhem Plateau spinifex and sandstone habitat affected by the project.
• Do not treat relocation alone as removal of the project impact, and retain evidence of avoidance, minimisation, clearance and monitoring outcomes.

Rehabilitation actions: Restore habitat structure

Rehabilitation should recreate connected spinifex habitat around retained sandstone features and should address fire, weeds and access. The available sources do not provide a species-specific planting schedule or rehabilitation target, so set measurable targets from pre-disturbance habitat condition and approval requirements.

• Retain and protect existing sandstone escarpments and boulders during rehabilitation, and avoid covering or destabilising the rock features used by the species.
• Re-establish native spinifex in areas that supported spinifex before disturbance, using locally appropriate material and methods approved by the land manager.
• Restore a continuous cover of spinifex around retained boulders and along habitat linkages rather than planting isolated clumps only at the edge of the development.
• Reinstate suitable loose rocks and other approved ground cover where these were removed, after checking that placement will not create erosion or safety hazards.

Rehabilitation actions: Fire, weeds and predators

• Develop a fire management approach that avoids repeated intense fire through retained and rehabilitated spinifex, while meeting legal and cultural burning requirements.
• Record fire timing, extent and intensity in retained and rehabilitated habitat, because the source identifies fire frequency as a factor requiring further investigation.
• Control weeds and prevent construction materials from entering spinifex patches or blocking movement between retained areas.
• Manage introduced predators and other introduced species where they are identified in the approved environmental management plan.

Rehabilitation actions: Monitoring and success measures

• Monitor spinifex establishment, patch connectivity, weed cover, erosion, fire history and use of rehabilitated habitat with fixed photographs and mapped plots.
• Repeat nocturnal searches in rehabilitated and retained habitat and compare detection results with the pre-clearance survey.
• Set success measures in the rehabilitation plan for native spinifex cover, survival, protection of sandstone features, weed control, fire outcomes and confirmed gecko use.
• Continue monitoring until the approval authority accepts that the rehabilitated habitat is stable and management controls are working.

Sources

• [PDF] A new phasmid gecko (Squamata: Diplodactylidae: Strophurus) from ..., mapress.com: https://mapress.com/zootaxa/2014/f/zt03878p048.pdf
• Table S1, Queensland Government: https://era.dpi.qld.gov.au/id/eprint/8305/5/WR20194_AC_Table_S1.xlsx
• Strophurus: australian spiny-tailed geckos., herpetonatura.wixsite.com: https://herpetonatura.wixsite.com/blog/post/strophurus-australian-spiny-tailed-geckos
• Arnhem Phasmid Gecko (Strophurus horneri), allanglescreatures.com: https://www.allanglescreatures.com/species/strophurus-horneri
• Strophurus - Wikipedia, en.wikipedia.org: https://en.wikipedia.org/wiki/Strophurus