brown rats on Rum are to be tagged and tracked by satellite to see if they are bothering one of the island's important bird populations.

It is one of the first projects of its kind anywhere in the world and is being commissioned by Scottish Natural Heritage (SNH).

The agency owns the island and wants to know the impact this particular rodent and other members of its species, have on the island's colonies of the Manx shearwater.

Rum is reckoned to be home to around a quarter of the world's breeding population of this seabird, from April until September, after they return from wintering off the east coast of South America.

They nest in burrows high up the Rum Cuillin, fishing by day and returning to their nests at night.

Brown rats, meanwhile, are more recent colonists, probably having arrived on boats. As on all offshore islands where rats have jumped ship, they have an adverse effect on native species.

Early data suggests rat numbers in the shearwater colony are low, which should be reflected in predation levels. So more information is needed before proper analysis can be conducted.

Lesley Watt, SNH Rum reserve officer, said: "Rats are thought to be responsible for numerous global seabird population declines through predation on eggs, chicks and adult birds, though historically they have not been thought to have an impact on the Rum Cuillin colony," she said.

"But we are concerned that rat numbers and predation may increase in the future. So we need to know more about the ecology of the rats to inform our future management policy for this globally import Manx shearwater breeding site."

She said the team was intrigued about what they would find out when "our roaming rat data" was analysed and the results seen. The rat-related work is part of a three-year Magnus Magnusson PhD studentship, funded by SNH and the Scottish Environment Protection Agency. Anglia Ruskin University is carrying out the work with the National Wildlife Management Centre, part of the Animal Health and Veterinary Laboratories Agency.

Mark Lambert, the PhD supervisor from the Animal Health and Veterinary Laboratories Agency, said: "Our work so far has found that Norway rat populations are relatively sparse within the high-altitude Manx shear-water colonies. But we want to be able to predict how rats might respond to any future environmental changes on the island."

Sean Carlisle, the PhD student conducting the research, said: "The best part of my research is trapping, releasing and tracking the rats as it is great to see them up close. It's even more exciting when you see what they get up to day to day."