A new device to reduce mammal predation on reptiles in pitfall traps

Context

Many vertebrate studies report predation from pit co-occupants as a source of mortality during pitfall surveys.

Aims

This study aims to assess the use of false-floors in pitfall traps to reduce the opportunistic predation of small reptiles by small mammals caught within the same pit.

Methods

Small-vertebrate surveys were conducted using pitfall traps in an arid landscape from 1998 to 2021. Between 2018 and 2021, wooden false-floors with 2 cm notches in their sides were placed inside pitfall traps to reduce the amount of reptile predation caused by small mammals co-occupying the same pit. The position of captured individuals, relative to the false-floor, were used to assess the capacity of false-floors to create an effective barrier between captured reptiles and mammals.

Key results

During the false-floor trial period (2018–2021), Pseudomys australis and Notomys alexis were identified as the key mammal species opportunistically predating on captured reptiles, collectively accounting for 54% of reptile predation incidents. Most of the N. alexis and P. australis captures were found above false-floors (92 and 70% of captures respectively), indicating that they were generally not able to access the prey refuge beneath. Reptile mortality from small mammal predation was significantly lower in pitfalls with false-floors (15% of reptile-mammal co-occupancy incidents) than in those without (60% of co-occupancy incidents). However, false-floors did not prevent all predation events because some mammals were able to access the compartment underneath the false-floors.

Conclusions

The false-floors provided an effective barrier between small reptiles and key mammal species caught in the same pit and reduced occurrences of small reptile predation.

Implications

False-floors can effectively be used as a tool to reduce reptile mortality during pitfall surveys. However, they also increased the time taken to set and check traps and we therefore suggest their use only during times of high mammal abundances, when the abundance of large rodents is high. The efficacy of false-floors at any particular site may be improved by trialling different-sized notches and construction materials.