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Prevention of unwanted species immigrating to islands on strait crossings


When islands are connected to the mainland by bridges or tunnels it becomes possible not only for humans to travel back and forth but also for wildlife, which uses these new means of access as migration corridors. The results can be disastrous, as can be seen from the example of the island of Tautra in the north of Norway (North Trøndelag).Tautra was proclaimed a wetlands area of international importance under the Ramsar convention in 1985. Parts of the island perform the multifunctional purpose of a breeding, migration, wintering and molting area, and have been used over the years by countless numbers of waterfowl. In the late 1970’s a road to the island was built over a stone-fill embankment. Predators, such as foxes, badgers, martens and others, began appearing on the island, using the new road as a migration corridor. The most abundant species of waterfowl on the island, which was the reason for the island receiving its Ramsar wetlands status, declined sharply in numbers after the construction of the road. Indeed, today some species on the island have been reduced to barely 10% of their original populations before the road was built. This drop in numbers is due not only to the introduction of mammalian predators but also to the deterioration of the area as a wetland feeding ground, an effect resulting from the blocking of the ocean stream when the embankment was constructed. A predator extermination program for the island was established. Also, to prevent predators from using the road, loudspeakers were set up in the hope that the noise from the speakers would be enough to scare the predators away. However, after a time the deterrent effect of the loudspeakers weakened, possibly as a result of the animals becoming used to the sound and no longer associating the sound with danger. In regard to roads and bridges, little research has been done on wildlife deterrent methods, which employ no physical barriers. Noise, light and smell have been used in different ways, but these measures seem to lose their effect over time. In tunnels, however, noise deterrents have proven successful. It has now (2001) been decided to replace 350 metres of the road out to Tautra with a bridge; a measure, which it is hoped will restore the natural water currents around the island. To ensure the success of this project, which will cost nearly 50 million Norwegian crowns, an effective wildlife barrier must be set in place. The Public Roads Administration has therefore initiated a development project with the aim of producing a wildlife barrier device that is 100% reliable. The device will be tested out on foxes, martens and badgers in captivity. The trials will be carried out at the University of Oslo during the course of the year 2001. Specifically, the tests are designed to demonstrate how well these three species cope with different kinds of grids (width of mesh, wire-thickness, length, breadth).

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