Simply deploying a large number of traps is insufficient when surveying reptiles. The choice of trap type has been shown to influence which species are frequently detected and, by extension, how the reptile community within a forest is interpreted.
A study comparing pitfall and funnel traps side-by-side at 107 sites in southwestern Victoria, Australia, recorded 1,130 individuals over a total of 6,276 trap-days. While total capture numbers were similar, fossorial (burrowing) species and active skinks showed distinct biases toward specific trap types. This clearly illustrates a fundamental principle of field ecology: the “number of captures” does not necessarily reflect actual numbers in nature.
30-Second Summary
- Pitfall and funnel traps were compared at 107 shrubland sites in southwestern Victoria, Australia, between November 2017 and March 2018.
- Over 6,276 trap-days, 1,130 individual reptiles—comprising 12 species and one snake group—were captured.
- Among the nine major species, four showed variations in estimated relative abundance depending on the trap type used.
- While alpha diversity—the number of species per site—was similar, the community composition and total species count were affected by the choice of trap.
- No single trap can meet all research objectives; the behavior of the target species and the research questions must be determined first.
What happened?
“Researchers at the University of Melbourne [reported this on] August 20, 2026. Austral Ecology They reported on the effects of pitfall traps and funnel traps on estimates of the relative abundance and diversity of reptiles. The analysis incorporated the possibility of uncaptured individuals—specifically, imperfect detection—into the statistical model.
Target Community Information
| Category | Details |
|---|---|
| Taxonomic Group | Order Squamata (Lizards and Snakes) |
| Key Families | Scincidae (Skinks), Pygopodidae (Legless Lizards), Agamidae (Agamas), Elapidae (Cobras/Elapids) |
| Study Area | Shrubby woodland in southwestern Victoria, Australia |
| Records | 12 species and one aggregated snake group |
| Subject of Analysis | 9 species with sufficient data |
| Conservation Context | Long-term monitoring amidst habitat fragmentation, fire, and climate change |
Research Method: Deploying two types of traps at the same site
The research team established a 200-meter survey line at each site and buried six 20-liter pitfall traps at 40-meter intervals. On the opposite side of the survey line, they placed six wire-mesh funnel traps arranged in three pairs. Both methods utilized drift fences to guide moving animals toward the traps.
Most sites were surveyed for five consecutive days, though schedules at 18 sites were shortened or interrupted due to heavy rain or extreme temperatures. Traps were checked twice daily, and individuals were marked to distinguish recaptures. The analysis accounted for detection conditions—such as date, maximum temperature, and rainfall—as well as site-specific differences.
Trap bias observed in 1,130 individuals
Total captures appeared similar: 548 individuals in pitfall traps and 582 in funnel traps. However, species-specific models revealed significant differences. The estimated relative abundance of the striped skink (Aprasia striolata) was five times higher in pitfall traps than in funnel traps, while that of the southeastern slider (Lerista bougainvillii) was 2.5 times higher. Their slender, elongated bodies, adapted for burrowing, may have made them more susceptible to capture in pitfall traps.
Conversely, the eastern three-lined skink (Acritoscincus duperreyi) showed 2.3 times higher abundance in funnel traps. Although the sample size for the southern water skink (Eulamprus tympanum) was only eight individuals, all were caught in funnel traps. No distinct trap-type effect was detected for the remaining five species.
Even if the number of species appeared similar, the communities differed.
“Each trap type detected an average of about four species per site, and using them together increased the count to 5.4 species. There was no significant difference in alpha diversity (the number of species per site). However, there were differences in beta diversity (differences in community composition between sites) and gamma diversity (the total number of species across the entire region). The estimated total number of species was 12.8 for funnel traps and 11.8 for pitfall traps.
This implies that a survey asking “how many species are there” does not necessarily require the same equipment as one asking “what combination of species is present.” The research team suggested that while funnel traps may suffice for efficiently estimating the number of forest species, using a combination of methods is preferable when identifying community turnover and specific fossorial (burrowing) species.
Why is this important?
Conservation priorities are determined based on species presence, relative abundance, and changes over time. If survey equipment systematically under-samples species with specific forms or behaviors, it can lead to misinterpretations of population trends or habitat effects. Australian government environmental assessment guidelines, for instance, require a combination of pitfall traps, funnel traps, and active searching when surveying threatened reptiles.
These results should not be applied as guidelines for keeping pet reptiles or capturing wild individuals. This study was an ecological monitoring project conducted under appropriate permits and ethical protocols. The key takeaway lies not in the capture techniques themselves, but in documenting the biases of observation tools, maintaining consistent methods over the long term, and designing multiple detection methods tailored to specific objectives.
Points to avoid overinterpreting
Field data were collected in the shrublands of southwestern Victoria during a single season (2017–2018). The same scaling factors cannot be applied to deserts or tropical forests, which differ in soil, vegetation, climate, and species composition. Data for the southern water skink were particularly uncertain (n=8). Although the total lengths of drift fences associated with pitfall and funnel traps differed, supplementary analysis showed that the length of internal fencing in pitfall traps did not significantly explain the results. Furthermore, this study did not formally compare cost-effectiveness.
4 Key Takeaways
- Even if the total number of captures is similar, there can be significant bias in capture rates across species.
- Burrowing species were more frequently estimated using pitfall traps, while some active skink species were better detected via funnel traps.
- Questions regarding species richness and community composition require different survey designs.
- Results must be re-verified if the study area or target species changes.
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