Estimating the potential for reinvasion by mammalian pests through pest-exclusion fencing

Abstract

Pest mammals are completely excluded from Maungatautari Ecological Island, New Zealand, by a 47-km Xcluder pest-proof fence; however, they are commonly sighted directly outside, along the fenceline. Permanent pest exclusion relies on maintaining fence integrity, and enhancing knowledge of pest activity and behaviour at fenced reserves. We describe summer and winter periods of activity and behaviour of mammalian pests directly adjacent to the pest-proof fence. We (1) tested for the effects of adjacent habitat type, breach type and season on the rate of mammalian pest sightings directly at the fence, (2) determined how quickly pest mammals may locate a fence breach, and how likely they are to exploit it, and (3) developed a predictive model to help assess the probability of a pest gaining entry to the sanctuary if repair to a fence breach is delayed. Observations inside the rolled fence hood provided firm evidence that rats travel and forage extensively in this artificial although highly acceptable aboveground habitat, much more than on the ground. We confirm and emphasise that mammalian pests are constantly testing the pest-proof fence. Pests are very common directly outside the fence, and within 24 h there is a very high likelihood that a fence breach will be located and exploited. The greatest threat of reinvasion comes (1) nocturnally, (2) from rodents and (3) in the summer; however, these results also confirm that there is constant risk from multiple pest species, regardless of time of day or season.

Tree-climbing capabilities of Norway and ship rats

“…In such 3D environments, ship rats can avoid or rapidly escape from Norway rats, permitting local sympatry wherever there is enough food both above and on the ground (Innes et al 2001). The hood of a pest-proof fence, 2 m above the ground and a good place for hunting nocturnal insects, was a veritable highway for ship rats (Connolly et al 2009), from which they were perfectly positioned for immediate access into the sanctuary through any breach in the fence caused by a falling tree. Contrary observations from the wild are consistent with our results in other ways.…”

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

“…Mammalian pests constantly test exclusion fences, pushing against them regularly, and are able to exploit a weakness within 24 h (Connolly et al . ). While this study detected feral animals outside of the reserve, there was no evidence of feral animals trying to breach the fence through the one‐way gates suggesting one‐way gates are unlikely to pose an incursion risk if they are maintained and checked regularly.…”

Estimating costs and outcomes of invasive American mink (Neovison vison) management in continental areas: a framework for evidence based control and eradication

“…The intention of the Mainland Island projects is to apply some of the pest management practices to intensively manage selected areas, with a focus on entire ecosystem restoration (Saunders and Norton 2001;Parkes and Murphy 2003;Parkes et al 2006). Management of Mainland Islands requires continuous pest control, because there is no barrier preventing recolonization exclusion fences have been successfully installed to keep mammalian pests out of some selected areas of high ecologic value (Day and MacGibbon 2007;Connolly et al 2009). …”