New shrew species suspected of posing risk to native variety

Damian McCarney

In Cavan County Museum

It is just a matter of time before a new, invasive species of shrew arrives in County Cavan, according to a respected environmentalist.
Having first been identified in Munster six years ago, the greater white toothed shrew has flourished in the Irish habitat, spreading as far north as County Westmeath in the intervening years.
The greater white toothed shrew is not native to Ireland, and how they arrived in the country remains a mystery, particularly given they are not native to Britain either. The threat they may pose to our native, pygmy shrew has not been established. However, initial signs are that it is displacing the pygmy species, which is significantly smaller.
John Lusby, raptor conservation officer with Birdwatch Ireland, told members of the group’s Cavan branch of the new shrew at a meeting in Cavan County Museum in Ballyjamesduff last Thursday night.
“Their native distribution would be in western continental Europe and North Africa,” Mr Lusby told the Celt after the meeting. “Obviously they got over here accidentally, but we don’t know the means of how they got here.”

Mr Lusby says that the shrew has “thrived” in Ireland. 

Discovered

The greater white toothed shrew’s presence in Ireland was first revealed through work conducted on barn owls in 2008.
“We were looking at barn owl diets and came across skulls of these mammals,” recalled Mr Lusby, “and that was the first record of them occurring in Ireland, so they are a fairly recent discovery.”
He continued: “They’ve become very well established, particularly in the core range, which is south Tipperary, east Limerick, but they’ve spread now. There is a separate population in Cork, there is a separate population around Mullingar, so they seem to spreading relatively quickly.”
Given the new shrew was located near Mullingar in a study conducted through Queens University Belfast in 2013, could they already be in County Cavan?
“Not that we know of, but it’s because they occur over such a large area already they are difficult to monitor their spread. We have done work monitoring where they occur, and where they don’t occur, through looking at raptor diet, which is how they were discovered in the first place. So we suspect they are not yet in Cavan, but we couldn’t say that definitively.”

Ecologists
Asked about the potential risk posed by the greater white toothed shrew, Mr Lusby said “It’s a very interesting situation”.
“Obviously with every non-native species there is potential for both positive and negative impacts. What we have seen is, it seems to be displacing the pygmy shrew, which is the only other species of shrew we have in Ireland... Wherever the greater white toothed shrew occurs in big numbers, pygmy shrews are absent.”
Do we know how they are displacing the pygmy species?
“Their relationship is not well known. The greater white toothed shrew is a more aggressive species, and about twice the size. There is quite an overlap in terms of food resources so there obviously is something going on there - it might be due to competition, but we don’t know the dynamic well yet in terms of negative impact on pygmy shrews, but it does seem to be the case.”

To get an idea of  the size of a pygmy shrew, here's a video of American's handling one:

http://youtu.be/z8NqorD6NVg