Rat Eradication Project on the Islands of Canna and Sanday - June 2000

Introduction
The islands of Canna and Sanday are situated off the West Coast of Scotland within the Inner Hebrides, close to the island of Skye. The islands are closely situated and are connected by a pedestrian footbridge. Both the islands are served by Caledonian MacBrayne ferry from Mallaig.
Over the past thirty years Aberdeen University has been collecting data on breeding seabirds through the 'Seabird Monitoring Programme Canna Studies'. The Highlands Ringing Group who carry out the seabird-ringing programme has been instrumental in the collection of this data. The data collected has clearly identified that some species of seabirds are in decline. The evidence collected strongly suggests that the main problem is predation on eggs and small chicks by rats.

Manx Shearwater is one species that is suffering mainly from rat predation. Manx Shearwater nest in burrows within a colony and are easy prey to rats. The Trust has tackled the problem by introducing rat bait boxes within the colony at the time of year when rats are looking for food after a long winter so they visit the Manx colony. This has helped to keep the rat numbers down and allow the Manx Shearwater to produce young, which is so important for the future of the colony.

Rat Eradication Programme
The Trust has implemented a programme in 1998 to eradicate all the rats from both Canna and Sanday. This is a huge programme involving extensive research, which is currently being carried out by the Trust to predict the impacts on other wildlife while using warfarin to eradicate the rats.

The Trust initiated a small mammal survey in 1999 on the island of Sanday and showed that the numbers of small mammals are low. The low numbers may be in part a result of rat predation and more in depth research was required. The Trust, along with Edinburgh University, is currently carrying out a large-scale mammal survey on Canna. A student is carrying out this research as part of their Masters degree.

Research into secondary poisoning in the food chain has been carried out in relation to birds of prey. The research has shown that rabbits who have ingested warfarin and have then been eaten by a bird of prey do not pose any threat to this species.

The next stage
A survey will now have to be conducted in the winter 2000/2001 to establish where the rats are on the island. Once these areas are established then they will be targeted with warfarin. The warfarin will be applied in containers or put directly down cracks and holes - none will be left on the ground surface and therefore will not pose a threat to livestock or pets. Checks of these sections will be made after the warfarin has been introduced to monitor the effect on rat numbers.

As Canna and Sanday are islands, a control programme will be introduced to ensure that once all the rats have been eradicated, rats will be prevented from invading the islands thereafter. The monitoring of rats will be ongoing to ensure that any missed will be eliminated through time. As a result both the island's wildlife will thrive for future generations to enjoy.

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