New shrew species discovered in Ireland
Even well studied island communities of terrestrial mammals are vulnerable to species introductions that may in turn lead to ecological degradation and loss of native species.
Eagle-eyed post-graduate students, Dave Tosh, Queen’s University Belfast, and John Lusby, University College Cork and BirdWatch Ireland, spotted the unfamiliar remains of Greater White-toothed Shrew Crocidura russula in regurgitated food remains (pellets) of Barn Owls and Kestrels collected at 15 locations in Tipperary and Limerick last autumn and winter. Seven Greater White-toothed Shrews were later trapped at four locations in Tipperary in March this year. The first Irish records of greater white-toothed shrew are now published in Mammal Review and provide compelling evidence that it is established in Ireland. Its absence from earlier surveys of owl pellets and small mammals in Ireland suggests a recent introduction by uncertain means. It seems likely that the greater white-toothed shrew will expand its range in Ireland. Its impact on the ecology of habitats in which it is found remains unclear but may be considerable.
Prof. Ian Montgomery of Queen’s University believes that these records “are evidence of at least one recent introduction event, probably accidental, from continental Europe to Ireland, and that this has resulted in a rapid increase in numbers over a short period.” He speculated that association with human habitation, social nesting and high reproductive potential of greater white-toothed shrews may have facilitated transport to Ireland amongst horticultural imports such as root balls of trees and subsequent rapid population expansion.
Prof. John O’Halloran of University College Cork, noting the high frequency of occurrence of shrew remains in bird of prey pellets, suggests that there is potential for the Greater White-toothed Shrew to “become a major prey item of avian predators in Ireland where there is an impoverished small mammal fauna compared to Britain”. John Lusby, Barn Owl Research Officer for BirdWatch Ireland, and John O’Halloran are currently carrying out research to identify factors behind the recent dramatic decline of Barn Owls in Ireland.
John Lusby of BirdWatch Ireland said, “This is a very significant discovery, which took us all very much by surprise. To find remains of one shrew would have been amazing, but the fact that 53 skulls were found in 10 Barn Owl pellets was phenomenal.” He further commented that “the Bank Vole, which was the last introduced mammal species to be discovered in Ireland back in the mid 1960’s, is now a significant element of the Barn Owl diet where it occurs”.
Initial analysis of Barn Owl pellets from roosts within the known range of the Greater White-toothed Shrew suggests that the introduction of this latest mammal may also prove particularly beneficial for threatened predators such as the Barn Owl. On this point, John Lusby said, “The Greater White Toothed Shrew is an important prey item for Barn Owls in parts of Europe, and from looking at Barn Owl pellets collected from sites in south Tipperary and Limerick it would appear that the Owls are taking them in quite high numbers."
On the downside, the Greater White-toothed Shrew has the potential to displace other shrew species such as the Pygmy Shrew, regarded as part of Ireland’s native fauna. Therefore, as in the case of other recently introduced mammal species in Ireland (Grey Squirrel, Mink, Brown Hare and Bank Vole), the presence of Greater White-toothed Shrew raises issues related to ecological impact and control. Further research on the origin, means of introduction, and potential impact of the Greater White-toothed Shrew on native biological communities in Ireland is required to clarify these questions. Having arrived, however, it is likely that Ireland is stuck with the Greater White-toothed Shrew regardless of whether it is for good or ill.