One‐way gates successfully facilitate the movement of burrowing bettongs (Bettongia lesueur) through exclusion fences around reserve

Abstract

When native herbivores are enclosed in fenced reserves without predators or dispersal options then overgrazing can occur, leading to damage to vegetation and co-occurring fauna species. One-way gates that allow medium-sized herbivores to exit fenced reserves may be an effective management tool to address overabundance or facilitate population expansion. We tested the use of one-way gates to facilitate the movement of the reintroduced burrowing bettong (Bettongia lesueur) from inside to outside a fenced reserve in arid South Australia. Oneway gates were installed in the exterior fence of the reserve and assessed using remote motion-sensor cameras. The influence of gate position (dune, swale or corner) and provision of food were assessed in relation to gate visits and exits. Animals were trapped inside and outside the gates to determine any population bias in gate exits. Baited gates recorded significantly more exits than unbaited gates and dune gates had higher exit rates than interdunal swale gates. When gates were unbaited, those installed in corners of the reserve showed significantly higher visitation by bettongs and a non-significant trend towards more exits compared to gates placed in straight sections of fence along dunes or swales. There was no sex or age bias of burrowing bettongs using the gates and bettongs travelled between 75 m and 1535 m from their warrens to use the gates. No non-target species gained access to the reserve through the one-way gates and only two non-target animals used the gates to exit the reserve confirming gate specificity for bettongs. During the same period, 96 burrowing bettongs exited the reserve through the one-way gates. One-way gates may be a management strategy for facilitating passive movement of medium-sized herbivores outside of fenced reserves for the purposes of reducing overpopulation or facilitating population expansion outside reserves.One-way gates were based on a combination of two gate designs tested during pen trials by Crisp and Moseby

Exploring the internal and external wildlife gradients created by conservation fences

“…Increasing the permeability of the fence could be achieved through one‐way gates (Butler et al. ), bridges, or ramps, methods used to assist the passage of wildlife across other anthropogenic structures (Mata et al. ; Glista et al.…”

Impacts of exclusion fencing on target and non‐target fauna: a global review

“…Similarly, bump gates in VCFs have proved successful in allowing free movement of stock whilst restricting wildlife movement (see VerCauteren et al ., 2009; Barasona et al ., 2013). One‐way gates such as those used for burrowing bettongs ( Bettongia lesueur ) (Butler, Paton, & Moseby, 2019), while worth mentioning, are not a true mitigation of this impact. One‐way gates do not allow the bidirectional movement of species and therefore do not fulfil the requirements outlined in our definition of barrier to movement.…”

“…As a flow‐on effect to barrier to movement, similar mitigation strategies to those mentioned above can be utilised. Species‐specific gates and gaps can be used to mitigate overpopulation of some species within fences, but notably for this effect, one‐way gates (Butler et al ., 2019) could be utilised as well. Overpopulation may also be mitigated through active population management, for example the relocation of individuals to other suitable locations (Treydte et al ., 2001), contraception (e.g.…”

“…One‐way gates have been used successfully in Australia (Crisp & Moseby, 2010; Butler et al ., 2019) and worldwide (Schumann et al ., 2006) to help mitigate over‐abundance and the dispersal of individuals to outside populations whilst still excluding the target species, although this would not alleviate genetic pressures on animals within fences (Dickman, 2012). As previously stated, the optimal scenario would be fence gaps or gates designed to allow non‐targets free bidirectional movement, while effectively restricting the target species.…”

Factors influencing the residency of bettongs using one‐way gates to exit a fenced reserve

“…1c). We deployed two Reconyx HC600 cameras at each gate while gates were open, one camera facing the inside part of the gate and one facing the exit point, with the following settings: high sensitivity, RapidFire, no delay between triggers and one image per trigger (Butler et al 2019).…”