Tag Archives: bank vole

In which we find woodmice, bank voles, field voles, and pygmy shrews but no harvest mice

As the alarm went off at 5.20am the other day, I did wonder why I had let myself in for such an early start on a precious day off. The rain beating against the windscreen as I drove through the dark, empty roads didn’t encourage me, either. I pulled up in the near deserted superstore car park, and it crossed my mind that this was not a normal thing to be doing.

The rain had stopped by the time I had got out of the car and wellified myself, and the remains of the supermoon cut cleanly through the sky. Our small group of like minded eccentrics congregated and headed off down an obscure path in the corner of the car park, lighting headtorches as we moved out of orange glare of the street lamps.

The path went under the dual carriageway, beside the river, to an isolated area of  waist-high marshy grasses, visible only in the small patches illuminated by head torch beams. After a bit of searching, we found the cached hoard of straw, food and weatherwriter, and stocked up the black bin bag. It didn’t look at all suspicious, four people walking around deserted wasteland at 6am in the morning carrying a black bin bag. I did wonder what anyone looking out of a window from the houses across the river must have thought.

We headed into the grass towards the scrap of striped tape that marked the first trap point, where two longworth traps (one on the ground, and the other set a couple of feet up on a stake) waited.

There’s always a frisson of suspense as you approach a small mammal trap. Has it been tripped? If so, what will it contain? We had a bumper harvest that morning – 8 woodmice, 2 field voles, 2 bank voles and one fiesty pygmy shrew. But none of the animals we were really searching for: harvest mice.

Field vole
Field vole

As the bright November morning dawned, we were able to get a better look at what we caught. If you think that one small mammal species is much like another in temperament, you’re mistaken. As you can see from these photos, voles are pretty chilled. I didn’t get any photos of woodmice (it was too dark when we found them, and they move too quickly). The tiny pigmy shrew was my personal favourite. You’ve got to admire a creature that, though about as big as a thumb nail, decides to try to bite its captor’s hand (it’s teeth weren’t long enough the penetrate the skin, but it gave it a good go).

Pygmy shrew trying to bite
Pygmy shrew trying to bite

The check was part of Surrey Mammal Group and Surrey Wildlife Trust’s harvest mouse project. We’re trying to get fur samples from harvest mice populations in different sites in the county. These samples are then DNA tested to allow us to see how closely related they are, or whether harvest mice at different sites have very different DNA to each other. The point of this is to see how good the connectivity between sites is for wildlife. Connectivity is important, as isolated populations are vulnerable to being wiped out.

This is our third year of the project. In the first year we were able to get enough samples for the lab scientists to identify plenty of DNA markers that will allow us to compare different harvest mice populations. Last year, when we went back to survey the sites that had had lots of harvest mice the previous year, we found very few. And we’ve not had large numbers this year, either.

We repeated the survey that evening, starting and ending in the dark, and found similar numbers of woodmice, bank voles, field voles and a single pygmy shrew, but again no harvest mice. The voles decided that sitting on hands was a morning activity – in the evening it’s all about climbing onto heads. This one seemed to particularly enjoy Derek’s hair – it looked like it was planning to settle down up there. Glen and Keith also got scaled by intrepid vole explorers.

A vole in the hair...
A vole in the hair…

By the end of the check it was bucketing down, and I was very pleased to get home to a warming bowlful of food, prepared by Dr C.

It’s not hugely surprising we didn’t find any harvest mice at this site – it really is cut off from other harvest mouse habitats (I suspect voles and woodmice are a little less particular in the sorts of neighbourhoods they’ll live in). And, while we didn’t succeed in our aim for the checks, it was still great to see small mammals at such close quarters. And it was worth braving the elements and giving up a lie-in to have that privilege.


How to tell who’s been nibbling your nuts

Hazel nuts are popular with many small mammals (our native dormouse, muscardinus avellenarius, is called the hazel dormouse for a reason). And the way a nut is opened can tell you who’s eaten it. This is particularly handy for telling if dormice are present, as you’re very unlikely to see one.

So, starting with the easy one. It takes strong jaws and teeth to split a hazel nut. So if you find a discarded nut shell split in two, or shattered, the nut has probably been eaten by a squirrel.

Bank voles also have big, strong teeth, so can bite rather than nibble through to the kernel. Quite often they will leave an irregular, roundish hole in the shell. They tend not to leave lots of teeth marks on the shell near the hole, unlike mice.

Now we get to the tricky part: distinguishing between nuts eaten by apodemus mice (woodmice and yellow-necked mice) and dormice. Both sorts of mice nibble neat round holes in the shell, so you need to look closely. A hand lens or magnifying glass helps.

Hazel nut that has been nibbled by a woodmouse or yellow-necked mouse: note the toothmarks on the inner slope of the hole, and scratch marks around the outside of the hole
Hazel nut that has been nibbled by a woodmouse or yellow-necked mouse: note the toothmarks on the inner slope of the hole, and scratch marks around the outside of the hole

A hole nibbled by an apodemus mouse will have teeth marks going down the edge of the hole (vertically). They leave more scratches on the outside of the shell than bank voles. Hopefully you can see both those features in this picture.

Nut nibbled by a dormouse. Note the smooth inner surface of the hole, and the scratches outside the hole.
Nut nibbled by a dormouse. Note the smooth inner surface of the hole, and the scratches outside the hole.

The inner edge of a hole made by a dormouse will be much smoother, as they gnaw around the hole, rather than down. But they do leave lots of scratches around the outside of the hole.

Another clue to help you tell the difference between apodemus and dormouse nibbled nuts is where you find them. If you find a cache of nibbled nuts, it’s likely to be apodemus. Dormice generally tend to eat and then drop nuts where they find them, so their nuts are often more spread out.

If you find a nut with a really tiny hole (maybe 1-2mm across), this has probably been eaten by an insect.

Nut A: who's eaten it?
Nut A: who’s eaten it?
Nut B: who's eaten this one?
Nut B: who’s eaten this one?

Here are a couple more close-up photos of nibbled nuts. Can you tell what’s eaten them? I will put the answer in the comments to this post. Let me know how you get on.

I’m starting to put together a page of photos of mammal signs. This will develop as I delve into my archive, and take more photos. I hope this will eventually become a useful reference (particularly as many books have line drawings rather than photos of these sorts of things, which can be rather hard to interpret). I’ll let you know when it goes up.