Rodents

The spread of invasive non-native species presents one of the greatest threats to biodiversity globally: invasive species are the primary driver of biodiversity loss on islands and the second largest everywhere else (CBD ; Millennium Ecosystem Assessment, 2005). Many of the UK’s island ecosystems have been damaged by the arrival and establishment of invasive non-native species. Introduced predators have caused particularly catastrophic damage to many species of waders and seabirds, undoubtedly causing numerous extirpations as well as contributing to ongoing declines(Stanbury et al. 2017).

Invasive species compete with endemic species and if successful can displace native species in the host region (Cororaton et al., 2009).

Aerial baiting from helicopters with a bait-sowing bucket and GPS to ensure coverage with anticoagulant toxins in cereal-based baits can reliably eradicate rodents on islands. Current best practice for temperate islands is to bait in winter when the rodents are not breeding, rodent numbers are lowest so competition for toxic baits is lowest, natural food is likely to be scarce, and many non-target species are absent from the island. However, short winter day lengths at high latitudes restrict the time helicopters can fly and poor weather in winter may increase risks of failure.

Invasive rodents are present on approximately 80% of the world’s islands and constitute one of the most serious threats to island biodiversity and ecosystem functioning. The eradication of rodents is central to island conservation eff orts and the aerial broadcast of rodenticide bait is the preferred dispersal method. To improve the efficiency of rodent eradication campaigns, the generation of accurate and real-time bait density maps is required.

Saving Scotland’s Red Squirrels (SSRS), launched in 2009, is a project to stop the decline of core populations of Scotland’s native red squirrel. It is a partnership project between Scottish Wildlife Trust, Scottish Natural Heritage, Forestry Commission Scotland, RSPB Scotland, Scottish Land & Estates and the Red Squirrel Survival Trust. The aim is the containment of the invasive non-native grey squirrel, which poses a dual threat to red squirrels through competition and disease transmission.

In locations with a high potential for re-invasion, such as inshore islands, sustained control of invasive species is as important as the initial knock-down for the long-term recovery of native populations. However, ongoing trap maintenance and lure replenishment are barriers to minimising the time and financial costs of long-term suppression, even when automatic traps are used.

Rodent eradications are a key island restoration activity to counteract extinction and endangerment to native species. Despite the widespread use of brodifacoum as a rodenticide for island restoration, there has been little examination of its potential negative effects on native reptiles. Here we examined the survival of two endemic insular lizard populations before, during and after a brodifacoum-based rodent eradication using a mark-recapture study.

Aerial broadcast application is currently one of the most common methods for conducting rodent eradications on islands, particularly islands greater than 100 ha or with complex and difficult topography where access by ground teams is difficult. Overall, aerial broadcast applications have a high success rate, but can be burdened by logistical, regulatory, and environmental challenges. This is particularly true for islands where complex shorelines, sheer terrain, and the interface with the marine environment pose additional risks and concerns.

Eradication techniques using ground-based devices were developed in New Zealand in the early 1970s to target invasive rodents. Since then, different bait station designs, monitoring tools and rodenticide baits have been developed, and changes in field techniques have improved and streamlined these operations. The use of these techniques has been taken around the world to eradicate rodents from islands. Eradication technology has moved rapidly from ground-based bait station operations to aerial application of rodenticides.