Our last few weeks have been very vole focused, with our annual Skomer vole surveys taking place on the island! The Skomer vole is a subspecies of the mainland bank vole endemic to Skomer. They are 20% larger than their mainland counterparts, mainly due to the lack of predation and the abundance of food on the island. We have been monitoring the population of Skomer voles since the 1970s, first carried out by Professor Tim Healing, later taken on by Dr Claire Risley, and now continued by the island team. These surveys help us see long term trends in the size, health, and demographics of the population.
The surveying is carried out in two plots, one with very dense bracken next to the farm and one with less dense vegetation in central fields west of the farm. 64 Longworth traps are laid out on a 6 x 6 grid in the evening for 5 consecutive nights, and are baited with carrot, celery, or oats - a proper vole feast!
In the morning, these surveys took place starting at 6.30am so that we had plenty of time to weigh, measure, and mark the voles before it got too hot for the voles in the traps. But this meant we were all slightly delirious so cue the creation of some of the worst vole related puns you could possibly think of (vole-au-vent, sausage vole, vole-derful).
The survey started by checking whether a trap had been tripped, they were then checked to see if anyone had made it home for the night! Some of the traps were tripped with no inhabitants, potentially tripped by shrews who then escaped through the shrew hole. Shrews have to eat every 2 hours, and so having a shrew escape-hole and enough space for them to work their way towards it is very important to protect these little guys!
Our primary inhabitants were, of course, Skomer voles, and sometimes wood mice! The wood mice were a lot more bouncy and less willing to play along with our handling and measuring of them, and they often escaped back into the bracken.
When we did get our hands on a vole, they would first be checked to see if they had any marks from the previous days, and given the appropriate haircut for that day. The voles marked with a little hair cut on their lower back or mid section on the left or right depending on the night. Some voles had all the haircuts and got slightly trap addicted, I like to think that they might all be slightly confused on the sixth night when their free meal and cozy bed has disappeared. We then checked their underside for either lactating nipples or testes to be able to sex them. It was very important that lactating females were released quickly and in the location of the trap so they could quickly get back to their babies!
The voles were then placed in a smaller plastic bag, where they could be manouevred into a sausage vole shape, to have the length of their body and their tail measured, and then were weighed inside the bag. After this our little voles were freed! Although, we were likely to see some of them again tomorrow.
This mark-recapture data gives us an insight into the population size and structure of voles on the island, and contributes to a decades-long database that gives a good insight into long term changes in the population. The data is yet to be crunched, but it'll be interesting to see how our voles are doing this year!
See you next time!
Georgina (LTV)