Field course focus: small mammal survey at Cranham Common

We arrived at Cranham to complete our four day field course for the Introduction to Biological Methods module. We were all full of excitement as for many of us this was going to be our first real taste of what it was to be a biologist.

We decided as a group that we wanted to do a small mammal survey of Daniels Grove, which is part of the Scout Centre up at Cranham Common. We wanted to find evidence of the biodiversity of small mammals, as well as look for the presence of any mustelids that could be present at the site.

When we arrived, we set about scouring the woods for potential test sites. We looked around for visible evidence such as mammal, tracts, nests, holes, latrines and discarded food. We were lucky in finding many signs of their presence, including, gnawed hazel nuts and cherry stones, as well as many possible holes. We also found the femur of a rabbit, which had two perfect holes 1cm apart which we believed to be the bite mark of mustelid, most probably that of a stoat.

Rabbit femur showing Stoat bite
Rabbit femur showing Stoat bite
Cherry stones, with bank vole and wood mouse bite marks
Cherry stones, with bank vole and wood mouse bite marks

We then set about using Longworth traps, after being trained how to use them safely. This are humane traps that allow the catch and release of small rodents. We had 10 that contained shrew gates. This meant that they could be left out over night for longer periods without fear of any shrews starving due to their high metabolic rate. We also had a further 10 traps that we could use during the day, these did not contain shrew gates, which meant that needed to be checked every 2 hours.

Checking Longworth traps in the Woodland Glade site
Checking Longworth traps in the Woodland Glade site

We used these traps over the three different sites, and were able to capture and release a total of 9 rodents, of which 3 were Yellow-Necked Mice Apodemus flavicollis and 6 were Wood Mice Apodemus sylvaticus; we also had a trap that was triggered but was unfortunately empty, but on investigation we found the scats of a species of Shrew Sorex sp. We were incredibly pleased with these findings, less so pleased when one of the Yellow-Necks made a run for it up my arm and across my shoulders. We noticed that there was a difference in the habitats in which we caught the different species. It appeared to us that the Yellow-Necked mice preferred woodland glade habitats while the Wood mice, preferred woodland riverine habitats, but we believe further study would be needed to establish whether this was truly the case.

A Yellow-Necked mouse caught in a Longworth trap (and Will Feirn!)
A Yellow-Necked mouse caught in a Longworth trap (and Will Feirn!)

We also used other methods to identify other small mammals. We used Hedgehog tunnels, which consist of a tube that has a strip of ink at each end with paper that was baited in the centre. This would allow small mammals to run through the tunnels leaving there footprints behind. From these we were able to establish that European water vole Arvicola amphibius were present, along with Weasel Mustela nivalis.  We also found track marks in the stream bank matching that of American mink Neovison vison.

Weasel track from a Hedgehog tunnel
Weasel track from a Hedgehog tunnel

When we combined these finding with other evidence that we found we were able to suggest that Yellow-Necked mouse, Wood mouse, Water vole, Bank vole, Stoat, Weasel and American Mink. As you can imagine we were very surprised by some of our finds.

We felt that the 4 days was a great success and enjoyed the fieldwork immensely. It has given us a real flavour of what is to come in our future careers, and we very much look forward to our future studies.

Will Feirn, Sarah-Jane Smith, Jasmin Stokes and Ellie Woolway (First year  undergraduates on our Bioscience courses)

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