The great Irish mammal watch

The same could be said for bank vole and a newly arrived shrew species (see panel). These new rodents may shrink the range of our native pygmy shrew. The new atlas should illustrate how the story unfolds.

“The primary value of what we are doing is to bring all existing databases together and so have contextual data for more detailed studies. If someone wants to do a study on squirrels or hedgehogs, at least they will have some distributional data to work from,” Lysaght concludes.

Visit the National Biodiversity Data Centre at biodiversityireland.ie

Wood mouse and pygmy shrew under pressure from non-native rodents

Scientists report that the wood mouse and pygmy shrew in Ireland are under pressure from two non-native rodents, the bank vole and greater white-toothed shrew. The effect is cumulative. When both invaders are present, native shrew and wood mouse are hit harder.

“The pygmy shrew disappears. It just goes completely where bank vole and greater white-tooth shrews are present. So they are putting this species in danger,” says Ian Montgomery from Queen’s University Belfast, who has studied the impact of these invaders. The number of mice falls to one-sixth what they would have been when the two species are about.

Experts questioned whether the continental shrew would survive an Irish winter, but Montgomery trapped plenty of them during the harsh winters of 2010 and 2011.

“It is very unlikely that the greater white-toothed shrew and bank vole will do anything other than spread throughout the country and there is not a great deal we can do to actually eliminate either species,” he concludes.

The mammal atlas currently being assembled with the help of citizen scientists should at least show us where the invaders are and highlight any future trends in our native small mammals.

Montgomery says we can manage the landscape to extend our indigenous wildlife species a helping hand toward survival. Planting more woodland in every county is one way of keeping the environment more in tune with their needs. “Allowing hedgerows to become a little bit overgrown is a good thing for wood mice but not so good for bank voles and greater white-toothed shrews,” he adds. The mammal atlas could help track the impact of changing habitat.

The bank vole arrived here from Germany, probably in the late 1920s. It now occupies the southwestern third of Ireland.

The greater white-toothed shrew was discovered here in 2007, but probably established a beachhead in Tipperary over a decade earlier. It likely hitched a ferry ride over from France in wrapped roots of trees. The bank vole is numerous throughout the southwest, while the French shrew reaches high densities wherever it occurs, says Montgomery.