The islands of Ipipiri (the Bay of Islands) were cleared of invasive rodents and mustelids in 2009. Since then, there have been over 50 incursions of predators to the island group. The Department of Conservation invited myself and others to visit the islands last week in anticipation of another bumper summer of cat, rat and mouse incursions. Incursions, are the first arrivals of invasive pests to a pest-free site. When the first mouse jumps off a ship, or rat swims ashore, then an incursion response must be launched.Poroporo from Urupukapuka island in the Bay of Islands (Photo by James Russell)
Project Island Song is a community project led by the Guardians of the Bay of Islands to protect and restore the islands. The community project, with support from the Department of Conservation and local tangata whenua (indigenous people) is currently a leader in New Zealand for protecting islands from pest reinvasion. Recent examples include a rodent of unusual size captured or a rogue cat swimming from a moored yacht. Our group first visited Poroporo, the spiny island which despite its small size has one third of all the rat incursions detected.
Next, we visited nearby much larger Urupukapuka, the island closest to the mainland separated by only 650 metres. There, the local iwi rat trappers tell us the story how each summer they respond within 24 hours to reports of rodent sightings on the islands. A quarter of incursions are first detected by vigilant members of the public.
As we talk on Urupukapuka, a secretive banded rail (Gallirallus philippensis) emerges from beneath a kayak on the beach, perhaps having helped us by performing its own biosecurity inspection.
The trappers tell us how they have been using a genetic databank of rats from the region to pin point where the rats they capture on the island might be coming from. This is done using new genecharts developed by the University of Auckland’s Department of Statistics and published earlier this year in Biometrics.
Evidence points to the incurring rats coming from deeper in the bay than simply the adjacent coast. Interestingly, the genetic signature of the Norway rats on the mainland has changed markedly in the past few years, suggesting complex dynamics in the mainland population may have led to the recent explosion in rat incursions on the islands. The team are hoping the coming summer won’t be as crazy as the last two, but are prepared if necessary to protect the islands once more, and the taonga species present on them. The public are reminded to stop, check and go when visiting the islands.