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The Field Vole specimen used to identify the mammal as a new species for Northern Ireland. Photo: Dr Angela Ross (Ulster Museum Belfast).

Owl research reveals new mammal for Ireland

Posted on: 09 Aug 2012

An examination of Short-eared Owl pellets from a recently-established breeding population in Northern Ireland has revealed a new mammal not previously recorded there.

During the summer of 2011, two pairs of Short-eared Owls nested in north-west and north-east Co Antrim. When Don Scott visited both sites under licence, he collected and dissected a total of 16 pellets, which showed that at least six of them contained the skulls and bones of a mammal which was unknown to him in Northern Ireland. After consulting several guides on mammal skulls and an owl and mammal expert in England, Dr Derick Scott, it was concluded that these unusual remains were that of Field Vole.

It was thought at the time that both pairs of owls might have regurgitated the pellets shortly after their arrival in the Antrim Plateau, probably from Scotland or elsewhere in Britain, but during the nesting season at the north-west site, two voles were seen scurrying across the forest track into long grass and rushes.

This site was ideal habitat for nesting Short-eared Owls as it had been replanted over a large area; it was also ideal for Field Vole. This small but important mammal is a valuable source of food for raptors and owls in Britain, but is has never been recorded in Northern Ireland or indeed the island of Ireland as a whole. The two pairs of nesting owls at both sites eventually fledged three and four young, respectively.

After discussing the find with members of the local 'Raptor and Owl Working Group' it was decided to wait until the 2012 breeding season to try and trap at least one of these voles alive, just to confirm the identification. With the help of Dr Angela Ross, Curator of Vertebrates at the Ulster Museum in Belfast, who kindly loaned us three Longworth traps, the group attempted to trap at least one of these elusive mammals a week later. The work was frustrating, as the team observed two much larger specimens hastily seeking cover in the trapping area on two separate days.

On 25 June 2011, the vole was donated to Dr Ross in the Ulster Museum for examination and identification purposes, with the Longworth traps also returned to the Museum. This much smaller specimen we took to be a young vole, which probably meant that they had already bred in this area.

But where had they come from initially? The only conclusion that we were able to come to was that they possibly arrived here accidentally from Scotland in bags of young saplings, as the area was privately owned by a Scottish forestry company and not by the Northern Ireland Forest Service as first thought.

Photographs of the vole and it's dentition (important in rodent identification) were sent to Dr Paddy Sleeman at University College, Co Cork for a definitive confirmation and several days later the mammal was declared a Microtus species.

The Short-eared Owls at the site were able to fledge five young, a record for the species in Northern Ireland, since they were first confirmed as a breeding species there in 1997.

Thanks to Don Scott for providing essential information for this story.

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1.Montgomery

13 Aug 2012 08:31

Some of the details are vague or imprecise. Was the field vole photographed captured in a Longworth trap at one site in 2012? If so, how did it die? Was it male or female, reproductively mature or immature? What weight was it? Were voles recorded at both sites? How large are the areas of grassland voles occupy? Is the grassland where voles have been recorded planted with young trees? Who are the local ‘Raptor and Owl Working Group’?

Researchers based at Queen’s University and elsewhere have worked extensively on the introduced Bank vole and Greater white toothed shrew in Munster. We have shown that these species have a major impact on wood mice and pygmy shrews to the extent that the latter disappears completely where both invasive species occur. Woodmice decline to about a sixth of the density in uninvaded areas where bank voles occur in Ireland. Hence, the small mammal community of the southern third of Ireland has changed in over 80% of suitable habitat. Further, the process of species replacement is continuing. No assertions about the impact of field voles on the reproduction of raptors or other predators can be made without data but it is likely that any positive effects will be more than offset by negative ones. Field voles are also regarded as forestry pests and may also be disease vectors. There is no doubt that species replacement of small mammals will have major top-down and bottom-up effects on all terrestrial ecosystems throughout Ireland.

The legal position on invasive alien species is reviewed in:
http://invasivespeciesireland.com/wp-content/uploads/2011/01/Review_of_IAS_legislation_and_governance_in_Ireland.pdf

Prof Ian Montgomery, School of Biological Sciences, Queen’s University of Belfast
i.montgomery@qub.ac.uk

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