Aboriginal-constructed lizard traps on Western Australia’s south coast create reptile habitat and teach principles of granite outcrop conservation

Cross-cultural collaboration

Directed by Merningar Elder LK and informed by a global literature review of lizard traps (Cramp et al. 2022), this study seeks to determine whether lizard traps provide reptile habitat, and share their associated cultural implications. To understand their role in the landscape and to ensure cultural protocols were followed, close cross-cultural collaboration has been maintained throughout the research. SC and LK selected sites together to ensure it was culturally appropriate to deploy cameras in these areas, and if special considerations were required. All sites were on Merningar/Menang/Goreng Country, including Two Peoples Bay Nature Reserve (Fig. 2). Once data had been collected and analysed, results were discussed with LK, whose perspectives were recorded.

Fig. 2.

Map of locations where time-lapse cameras were deployed. Numbers in brackets indicate the number of granite outcrops in that location. Grey shading indicates granite surface bedrock (Geoscience Australia 2012). Research was based in Kinjarling/Albany, Merningar/Menang Country.

Data collection methodology

Reptile taxa and behaviour at lizard traps, natural exfoliation, and bare granite were recorded using Brinno TLC200 time-lapse cameras. Habitats were classed as: (1) lizard traps (i.e. propped-up rock slab of 50–150 cm in diameter/width); (2) natural exfoliation (i.e. un-propped rock slab chosen to be roughly the same size as a lizard trap); and (3) bare granite. We followed a pilot study where thermal cameras and time-lapse imagery were used simultaneously at the same location; the former were not reliably triggered by reptiles that were observed by the latter (SC, unpubl. data).

Cameras were deployed at 45 granite outcrops with the most (n, 12) located at Two Peoples Bay Nature Reserve (Fig. 2). At each granite outcrop, there were three camera sites comprising a lizard trap, a natural exfoliation,and a bare granite site, resulting in a total of 135 camera sites. The 45 granite outcrops were distributed between eight areas across Merningar Country between December 2022 and April 2023 (Fig. 2). Granite outcrops were in nature reserves (Two Peoples Bay), national parks (Waitch Nolar, Waychinicup, Torndirrup, West Cape Howe, and Mt Lindesay), unallocated Crown land (Calyerup), and private property (Youngs Lake). To minimise the risk of camera theft and reduce influence of human presence on reptile behaviour, areas frequently used by the public were avoided.

To compare reptile activity between the three habitat types, camera sites at the same granite site were situated within 10 m of each other. Cameras were deployed for between 5 and 10 days and took one photograph every 1 s. To ensure cameras were observing the same size area, cameras were placed 1 m away from the habitat they were monitoring, and on a stand 40 cm off the ground. During the study period, cameras were deployed at three sites simultaneously per week. Granite outcrops were a minimum of 100 m apart that included a minimum of 20 m of vegetation separating each granite outcrop.

A thermal camera (Seek CompactPRO XR) was used to photograph the plan and oblique view of each habitat at each granite site (Fig. 3). The plan view photograph was taken facing directly down from chest height of co-author SC (130 cm). The oblique view photograph was taken from ground level 50 cm from the habitat. Thermal images provided thermal data for a single point in time for each habitat at each site. Timing of photographs was also recorded.

Fig. 3.

Pairs of thermal images of different habitats on granite outcrops from oblique (left) and plan (right) view. (a) Lizard trap; (b) natural exfoliation; (c) bare granite. Each photograph has a scale bar on the left-hand side indicating temperature in degrees Celsius, with hottest being red/white and coldest blue/black. Located at Calyerup 2.

Data processing

To establish reptile diversity, occurrence, and behaviour at the three habitat types, a day of time-lapse footage from each camera at each site was analysed. The second day of deployment at each site was selected, to ensure influence from human presence during camera set up and collection was standardised, and to maximise the number of sites with available days of footage. With increasing number of deployment days there was a greater chance of failure due to cameras falling over, batteries running out, SD cards filling up, or random camera failure. All reptile activity on Day 2 time-lapse footage was recorded, including the time each reptile appeared and left, behaviour, species (where possible), and the weather during that time. Camera failure occurred nine times. Footage was analysed from 42 lizard trap, 41 natural exfoliation, and 43 bare granite sites. Due to inadequate image resolution, small skinks were identified only to family level. To calculate thermal range of habitats at a single point in time, the highest and lowest temperature in each thermal photo was recorded.

Data analysis

R studio 4.2.0 (R Studio Team 2022), and R packages ‘lubridate’ (Grolemund and Wickham 2011), ‘dplyr’ (Wickham et al. 2023), ‘hms’ (Muller 2022), and ‘tidyverse’ (Wickham et al. 2019) were used for data analysis. Summary statistics were performed using base R. To test if species occurring at lizard traps, natural exfoliation, and bare granite were different, the correlation between habitat and number of sites for each observed species was tested using Pearson’s correlation. To test if there was a significant difference between lizard traps, natural exfoliation, and bare granite in number of reptile occurrences, duration of reptile visits in seconds, number of reptile species, and thermal range in degrees centigrade, Wilcoxon signed rank tests were performed, comparing those metrics between habitats at the same site.

Reptiles are commonly observed at lizard traps

Time-lapse cameras deployed on granite outcrops showed that reptiles are commonly observed at lizard traps. A total of 27 of 42 lizard trap sites had reptiles present within 1 day of footage, with a total reptile presence of over 15 h, and reptiles observed at lizard traps 4% of the time. Reptile activity was similar between lizard traps and natural exfoliation. Total duration of reptile presence was slightly greater at lizard traps than at natural exfoliation. Reptile activity was much lower at bare granite than lizard traps and natural exfoliation (Fig. 4).

Fig. 4.

Overview of reptile presence at lizard traps (purple), natural exfoliation (green), and bare granite (yellow). Black line bars indicate standard deviation. Data from Day 2 only.

At least five species were observed at lizard traps: Varanus rosenbergi, Egernia kingii, Ctenophorus ornatus, Notechis scutatus, and Ctenotus labillardieri (Figs 4–6) along with the unidentified reptile and small skinks categories. Only two areas (Calyerup and Waitch Nolar) were within the range of C. ornatus.

Fig. 5.

Reptiles observed at lizard traps using time-lapse cameras. Sites clockwise from top left: (a) Two Peoples Bay 1, (b) Mt Lindesay 2, (c) Calyerup 3, (d) Mt Lindesay 2, (e) Torndirrup, 9, (f) West Cape Howe 3.

Fig. 6.

Percentage of sites reptile species were present at lizard traps, natural exfoliation, and bare granite.

There is no difference between reptile occurrence at lizard traps and natural exfoliation

Analysis of reptile occurrence, presence, diversity, and thermal range showed no difference between lizard traps and natural exfoliation. There was a significant difference between lizard traps and bare granite, and natural exfoliation and bare granite (Table 1).

Small skinks and E. kingii were the most observed reptiles at lizard traps and natural exfoliation (Fig. 6). A similarity index of presence (% sites that species where present; Fig. 6) at lizard traps, natural exfoliation, and bare granite showed no difference between lizard traps and natural exfoliation in observed reptile assemblages (Pearson’s correlation of lizard trap against natural exfoliation = 0.99, lizard trap against bare granite = 0.83, natural exfoliation against bare granite = 0.78).

Reptiles use lizard traps for thermoregulation and shelter

Reptiles were observed in time-lapse photographs basking on, near, and entering and exiting lizard traps. There were more occurrences of reptiles entering lizard traps than exiting. There were more observations of basking at lizard traps than at natural exfoliation (Fig. 7).

Fig. 7.

Counts of different behaviours observed at lizard traps, natural exfoliation, and bare granite. LT, lizard trap; slab, naturally exfoliated plate of rock.

Learning from lizard traps about caring for granite country

LK shares that reptiles use lizard traps because they must bask in Boornura [Autumn] to obtain enough energy to hibernate over winter. Lizard traps offer suitable retreat sites to bask near because if they are disturbed by predators during this vulnerable activity, they can quickly and easily find safety (unless that predator is a human). For the Knapp family, constructing and maintaining lizard traps is about survival as they provide a reliable food source in Boornura [Autumn] (Fig. 8). LK’s recollections align with data collected for this study showing that reptiles use lizard traps for basking near, or on, and for going underneath (Fig. 7). Karda (V. rosenbergi) are the most sought-after reptile that use lizard traps, followed by Wargyl (Morelia spilota), Yoorn (bobtails, Tiliqua rugosa), Noorn (N. scutatus), and Dubitch (dugites, Pseudonaja affinis). Yondi (E. kingii) commonly use lizard traps but are only eaten if people are very hungry. Kuttiny (C. ornatus) use lizard traps, and LK has fond memories of chasing these as a child, and her children doing the same. Kuttiny (C. ornatus) were never eaten and there were repercussions from the Elders if caught harming them. Many other smaller reptiles use lizard traps, such as geckoes and frogs; these were not eaten, but recognised as food sources for larger reptiles. Birds of prey, while using thermals from granite outcrops to gain altitude, hunt basking reptiles off the rocks. Lizard traps also provide refuge for reptiles from aerial predators.

Fig. 8.

Perspectives from Merningar Elder Lynette Knapp about lizard traps.

Lizard traps provide habitat for reptiles

Time-lapse camera photography has given important insights into reptile activity at lizard traps, revealing novel data on reptile occurrence, species, and behaviours exhibited. Previous publications often mentioned observations of reptiles using lizard traps (Cramp et al. 2022), and Guislain et al. (2020) carried out inconclusive thermally triggered camera studies investigating lizard traps as reptile habitat. Importantly, these data are unsurprising to LK, with Traditional ecological knowledge previously shared by Merningar and Menang Elders that included all the species and behaviours observed in this study (Cramp et al. 2022). Further species and behaviours are outlined in traditional ecological knowledge, including pythons (Morelia spilota), dugites (P. affinis), and bobtails (T. rugosa) using lizard traps to evade aerial predators, and forage. Co-authors have also observed additional species using lizard traps that included M. spilota (Waargyl [carpet python]) retreating beneath a lizard trap on a warm winters’ day, Egernia napoleonis (crevice skink) using a lizard trap to ambush flying insects, two observations of P. affinis (Dubitch [dugite]) basking near lizard traps before retreating down a small hole (presumably their burrow) next to the lizard trap, and Elapognathus coronatus (crown snake) using a lizard trap as a midway shelter whilst travelling across a granite outcrop (SC and SDH, unpubl. observations).

Identification of small skinks to genus or species level would further outline the biota supported by lizard traps, such as Christinus marmoratus (marbled gecko) and Underwoodisaurus milii (barking gecko) (Cogger 2018). However, this would be culturally and ecologically disruptive as investigation into detailed species identity typically requires lifting rocks; Government guidelines for survey of threatened reptiles state that this practice is destructive to habitats and the species that use them. Turning rocks is still an accepted technique (Australian Government 2011), but we suggest finding alternative survey methods to minimise destructive impact on both environmental and cultural grounds.

There is no difference between lizard traps and natural exfoliation

Lizard traps can provide shelter for much larger reptiles than natural exfoliation, such as the desired food species Karda (V. rosenbergiFig. 8) when propped up about 10–20 cm. We saw slightly more Karda activity at lizard traps than natural exfoliation (present at 12% compared to 8% of sites respectively), but further investigation is required to understand if lizard traps facilitate Karda occupancy and if this species prefers lizard traps over natural exfoliation (Guislain et al. 2020).

Reptiles use lizard traps for thermoregulation and shelter

Thermal data aids understanding as to why reptiles are using lizard traps. Lizard traps significantly increase thermal complexity compared to bare granite. That gives reptiles greater control over their thermoregulation, which is a key part of surviving and reproducing (Thierry et al. 2009; Lelièvre et al. 2010). Reptiles need to maintain a body temperature between 20°C and 30°C and this is primarily done through poikilothermy, aided by behaviours of basking, adjusting posture, and finding favourable microclimates (Dawson 1975). On hot days, the surface of bare granite was over 40°C, while lizard traps varied from 22°C to 64°C and provided a cool space to generally maintain optimum body temperatures. In the context of a warming climate, this indicates the potential importance of lizard traps as thermal refuges (Huey et al. 1989; Selwood and Zimmer 2020). Here, we documented the range of temperature provided by lizard traps and recommend further study on thermal complexity over time of day, weather, and different seasons to elucidate when and why reptiles are using lizard traps, and how they add to the thermoregulatory environment of granites.

Learning from lizard traps about caring for granite Country

Lizard traps teach us that caring for granites involves long-term (multi-generational) thinking, minimising disturbance, and deep understanding of ecosystems. Lizard traps are rock formations that are initially constructed, possibly thousands of years ago (Smith 1993), in very precise locations chosen for their thermo-regulatory properties and proximity to reptile activity (LK, pers. comm.). Traps are subtle structures, and to the untrained eye may appear like a natural rock. Although not commonly used today, pre-colonisation they were used to catch reptiles as people moved through their tracts of lands along the coast (Robertson et al. 2021). Lizard traps were only used in Boornura [Autumn] before the rains arrived and reptiles were sunning themselves ready to go underground for winter (LK, pers. comm.). This meant most of the year lizard traps were undisturbed by people.

Merningar ways of interacting with granites are very different to contemporary use. Today granite outcrops are mined, used for water storage, damaged by vehicles, while loose surface rocks are stacked and removed (including lizard traps) and moss mat vegetation communities are disturbed (Porembski et al. 2016; Michael and Lindenmayer 2018; Cramp et al. 2022). For Merningar Custodians, granite outcrops are places of learning, spirituality, and reverence, where you tread lightly and minimise your impact (Knapp et al. 2011; Cramp et al. 2022).

Bringing together traditional ecological knowledge and novel scientific techniques can be powerful in understanding and caring for Country (Ens et al. 2012; Walsh et al. 2013; Ens and Turpin 2022). This seems particularly relevant to granites, where the Aboriginal peoples and colonial settler worldviews have opposite ways of interacting with these ancient hotspots of biodiversity and cultural values.