Data on immunological expression and phenotypes in a natural population of field voles in Kielder Forest, UK 2015-2017

Wild field voles Microtus agrestis were trapped in Kielder Forest, Northumberland, UK. Trapping was conducted over a total of 46 sessions from March to October in 2015-17, at approximately two week intervals. At each session we trapped voles at four different sites at least 1 km apart. During the course of the study, three sites were reassigned due to practical constraints, giving a total of seven different sampling sites. At each site, 197 Ugglan traps were laid out in a grid pattern with approximately 5m between traps. Trapping sessions lasted three days, with traps checked morning and afternoon.

Voles were marked with unique PIT tags on first capture. On the first capture of each session for a given individual, we recorded sex and reproductive status (ascended or descended testes for males; pregnant, lactating, perforate or imperforate vagina for females) from visual inspection. We measured body length from snout to vent and total body mass. A small blood sample (up to 50 µl) was taken from the tip of the tail and stored in RNAlater at -20°C for a maximum of 5 days before being transferred to -80°C for longer term storage.