CritterCam - the search for a water vole. Part 1

This all began in May, when I was doing my bird count near the Wark Forest for the BTO Breeding Bird Survey.  At one point I glimpsed a small mammal running across the track out of the corner of my eye.  It was dark, vole-shaped and rat-sized so I wondered if it could be a water vole.  There is a very small stream running through a pipe under the track, no more than 300mm in diameter, and because of the dry spring weather there was almost no water flow.  The habitat is poor unimproved wet grassland with mostly rushes rather than grass at that point, not a habitat I associated with water voles.  (I used to see them 50 years ago in a slow-flowing lowland river.)

Although the BTO BBS records mammal sightings I wasn't confident enough to record a water vole.  I did, however, send a message to Kirsty Pollard, a water vole expert at Durham Wildlife Trust and she passed my email on to Kelly Hollings, Northumberland Wildlife Trust's Project Officer in the Restoring Ratty water vole re-introduction project in Kielder.  Kelly was very encouraging and said the habitat was good for water voles, similar to some of the release sites in Kielder, so I went back with three trail cameras in July.  The cameras were in for a week, one close to where I thought I might have seen a water vole and two on a slightly larger but still very small stream (<500mm across) a couple of hundred metres away.  They recorded hundreds of videos and on a first look through I couldn't see much very exciting.  There were lots of glimpses of small mammals and I could identify field voles and wood mice, as well as reed buntings, meadow pipits and a roe deer's ankles.

Before giving up I had another look through the videos and could pick out a few where the voles looked bigger.  They were all on the on the trickle of a stream where I had my first sighting and there was very little on the other cameras.  It is difficult to judge scale although there is a slice of apple visible in the first clip.  I sent a very brief extract to Kelly and she replied that she was 99% sure it was a water vole.

So I went back earlier this month with two cameras and put them both on the first stream.  In most places it is difficult to see any water at all as it runs underneath the vegetation.  I spent time clearing a view and making sure the apples were better positioned.  Between them the cameras recorded almost 700 video clips so it is taking a while to work through them.  The first camera was set up here.

There are plenty of images of voles but I think they are probably all field voles.  Bank voles are 8-11cm long (head and body) with a tail 50% of body length, field voles are 9-11.5cm long with a tail <40% of the body length and water voles are 14-22cm with a tail 60% of the body length.  On the video it wouldn't be easy to tell a field vole from a bank vole or a juvenile water vole without seeing the tail but in some images the tail is clearly visible and is short.  (The other name for a field vole is short-tailed vole.)  The first two voles in the video are small whereas the last one which appears briefly nearer the camera looks larger although it still clearly has a short tail.

I also put a piece of raspberry cane next to the apple, 150mm long to act as a scale but the voles didn't approve of my measuring stick and moved and then removed it.

One very interesting sighting was of three shrews - water shrew, pygmy shrew and common shrew.  You can see that shrews don't eat apple but they are very curious (and very fast).  To find all three species in the same place on the same night was a pleasant surprise.

There are another 390 videos from the second camera so I'll report back soon on those.