Abstract:
In this paper, we review and analyse how three species of invasive rat (Rattus rattus, R. norvegicus and R. exulans) disperse to and invade New Zealand offshore islands. We also discuss the methods used to detect and prevent the arrival of rats on islands. All species of invasive rat can be transported by ship. However, rats can also swim to islands. Swimming ability varies greatly between individual rats, and is probably a learned trait; it is unlikely to be affected by variation in sea temperature in this region. Norway rats (R. norvegicus) are the best swimmers and regularly swim up to 1 km. Therefore, to prevent recurrent swimming invasions of islands, source populations may need to be controlled. Since islands differ in their attributes and individual rats differ in their behaviours, multiple devices need to be used to detect and prevent the invasion of islands, including poisons, traps, passive detection devices and trained dogs. In New Zealand, 85% of rat incursions have been successfully intercepted using traps and/or poisons. Any response should cover at least a 1-km radius around the point of incursion. If trapping, it is recommended that jaw traps are used. If using poison, it is recommended that hand-spread, short-life, highly palatable bait of the maximum permissible toxin concentration in small pellet form is used; if bait stations are used, large wooden tunnels that have a line of sight through them are recommended. To intercept invasions early, it is recommended that island surveillance is undertaken at least annually (preferably every 6 months).
