On Sunday 23^rd May seven of us met up at Tamar Lakes in North Cornwall (SS 293 114) to see what we could find in the way of mammals and, hopefully, to collect a few records for this relatively poorly surveyed part of the County.
South West Lakes Trust manage Lower Tamar Lake as a bird and nature reserve as well an angling lake and they were kind enough to give us permission to put out traps and to explore the site. We had set traps in three sites around the lake late in the previous evening – each with four Longworth traps generously stocked with hay, rabbit food, carrot, and live meal worms. The traps were set to trip at 5g, which we hoped would allow us to catch any water shrews which investigated. Around each trap entrance a little rabbit food was placed as an enticement.
The traps were set in a 5 m circle around two refugia. Each refugium consisted of a piece of corrugated bitumen roofing sheet approximately 1 x 0.6 m – small enough to be carried around the site. Under the corrugated sheet was placed a plastic bait dish containing live meal worms. The dish was placed on a paper picnic plate – the idea being that any animal investigating the bait would leave its droppings on the plate. We were particularly keen to see if we could record water shrew and to evaluate the method for general recording – it is cheap, easy, and relatively resistant to tampering or theft.

The first group of traps were set around an open area which bordered willow scrub at the eastern inlet to the lake. The refugia were set in the wet woodland and the traps in grass tussocks. Checking the traps was a disappointment – none had been tripped and there was nothing under the refugia. However we did find abundant prints from the roe deer that we had seen whilst setting the traps in the evening. Pete and Tim also found otter prints in the wood and we spent some time trying to get photographs of what we think were rat prints in the woodland mud. Jenny and I spent some time looking for evidence of vole runs in the tussocks and were rewarded with filed vole food caches – grass pieces with a characteristic 45^o cut.

Coming back across the dam on the south side of the lake we could see plenty of mole hills and we looked for, and failed to find, evidence of rabbits which often leave droppings on mole hills. Our second trap site was in the wet woodland next to the smaller pond on the south west side of the lake. The traps had been set around recently felled timber piles and along the bramble hedge amongst willow. Again there was no evidence of the refugia being used but we did have one success with the traps – that set in the bramble. This was an enormous(e) female wood mouse – probably pregnant, which we weighed at 32 g. We found no clear evidence of other species in this area.

Our final trapping area was in the willow/hazel woodland near the path, north west of the lake. Here we trapped 3 more mice, again large ones – two females at 20 and 26 g, and a male of 27 g. Under one of the refugia droppings were found around the bait dish. These were 5-6 mm long and 1.5 mm across. Under the dissecting microscope it was not possible to identify any insect remains and the droppings dried hard – they were probably wood mouse. On this brief experiment with baited refugia it certainly seems worth persevering and I intend to carry out some more tests in the garden!

After the trapping we retired to the car park to refreshments (thanks for the cake Jenny!) and to discuss our findings. Tim Dingle also told us something about the history of the lake and his work with the Bude Canal Trust.

Later some of the party returned to look for feeding signs in the woodland below the spillway. Amongst the hazel scrub, nut shells provided us with evidence of grey squirrel, wood mouse and (most excitingly) dormouse. There was no evidence of bank voles, which we thought a little unusual.

Overall this was a very successful survey trip – the weather was beautiful and we collected plenty of evidence for the Records Centre which will help us build up a picture of mammal distributions across the North of Cornwall. I hope that we can return later in the year and see what else is on the site.

Thanks to everyone who turned up, and thanks to Lisa at SWLT for permission to use the site.

Wood Mouse (Apodemus sylvaticus)      
Live trapping and droppings

Roe Deer (Capreolus capreolus)              
Live sighting and tracks

Fox (Vulpes vulpes)                                    
Scent marking

Hazel Dormouse (Muscardinus avellanarius)      Feeding signs

Field Vole (Microtus agrestis)                    
Feeding signs and trackways

Otter (Lutra lutra)                                         
Tracks

Mole (Talpa europea)                                 
Mole hills

Grey Squirrel (Sciurus carolinensis)         
Feeding signs

Dave Groves, Cornwall Mammal Group