Thursday, 21 June 2012

Extending our knowledge of a rare mouse

The other evening I received an email from a friend to which was attached a photograph of a dead mouse, brought in by their cat. There was nothing unusual in this except that the mouse had a broad yellow collar across the throat. The friend had noticed that this mouse was somewhat different from the wood mice that her two cats often delivered and she wondered if it might be a yellow-necked mouse. Although closely related to the wood mouse, the yellow-necked mouse is a slightly larger, more robust species, with a distribution restricted to the south of England and parts of Wales. The photograph certainly suggested that it might be a yellow-necked mouse so I asked that it be put in the freezer until I was back in the brecks and could take a look.

Further inspection revealed that it was indeed a yellow-necked mouse and one of only a handful of records of this species within the county. We are right on the edge of the range of this species but now have records from across the southern part of Norfolk, extending as far north as near Watton. One of the key features of this species is the broad yellow neck collar, which extends right across the throat to reach the darker dorsal fur on both sides of the neck. A mature male wood mouse can have a sizeable yellow throat patch, but this does not reach the darker dorsal fur to form a wide band.

One of the interesting things about this species is the contrast between the strongly southern distribution in England and the fact that it occurs further north in Scandinavia than the wood mouse. There is evidence that within England the species is most strongly associated with mature deciduous woodland, notably long-established or ancient woodland, and that it is absent from many of the more ‘open field’ habitats utilised by the adaptable wood mouse.

The hunting range of the cat which brought in this mouse almost certainly overlaps with a site where small mammal traps have been deployed on numerous occasions, without ever catching a yellow-necked mouse. It might be that the mice are present at a very low density – their home ranges are larger than those wood mice, so densities are lower – or that the very high densities of bank voles at the site excluded them from the traps. Either way, we do need to take another look with the traps to see if we can identify where these mice are and in what numbers. While cat predation remains a drain on small mammal populations, on this occasion it has identified the presence of a rare species in this part of the county.

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