Country diary: This could be a case of mistaken rodentity | Nic Wilson

Bank vole or wood mouse? That is the question. I’m working my way through a series of nine-second videos from Clophill Lakes nature reserve, taking notes on how many bank voles appear in the clips. Unfortunately, I can’t tell my voles from my mice.

The footage begins at 4.47pm, when wildlife volunteer Stephen Plummer switches on the trail camera in his mostela trap: a wooden box with a drainpipe entrance leading to a scattering of nuts and seeds. Both wood mice and bank voles star in the Clophill Saga – a rodential drama set in deciduous woodland beside old ponds – but I’m struggling to tell the two species apart, especially in the monochrome infrared light. I take notes as they enter: BV, 2BV, WM, BV. Or is it WM? I check the differences between them for the umpteenth time – 216 clips later (at 4.46am), I reckon I’ve got my eye in.

If the bank vole’s shorter, stubby tail, low-set ears, stout snout and smaller eyes aren’t visible to distinguish it from a wood mouse, its movements are diagnostic. It scurries rather than scuttles, giving the impression of having a lower centre of gravity. It’s also one of the most endearing animals I’ve ever had the pleasure of watching.

Stephen tells me that in his experience bank voles are usually gentle and placid in the hand. And unlike the mostly nocturnal wood mice, they’re cathemeral (intermittently active by day and night). This is borne out by the footage. By the time the first wood mouse shows up 7.12pm, the two voles have cached all the peanuts and only a nibbling of seed remains.

But the wee small hours belong to the mice, though a brown rat pokes its grotesquely oversized head, Alice-style, into the drainpipe at one point like a wood mouse that’s eaten all the cakes. Despite the size difference, rats and mice belong to the same family (Muridae), which also used to include bank voles (originally Mus glareolus – the gravelly mouse). Even the word “vole” is thought to derive from the Norwegian vollmus meaning “field mouse”. It’s good to know that I’m not the only naturalist who’s had to take a second look.

• Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024, is available now at guardianbookshop.com