So we’re into Autumn, and I doubt there’ll be any more sighting between now and February/March next year.
It’s not that water voles hibernate, as such, but they do start to spend a lot more time underground. With food being in shorter supply during the cold months, they have to find ways of conserving energy. Calorie-wise, stores of tubers, bulbs and rhizomes will keep them going, but the voles will still need to pace themselves. Radio tracking suggests that during the deepest winter they spend three or four days at a time in their nest chambers, presumably sleeping, and packed in alongside other, sometimes unrelated water voles for warmth. This might sound surprising for an animal usually so territorial, but during the shortened daylight hours, hormone levels are low and won’t be triggered again until February. For now the voles have nothing to do but tick over.
When they do move about it tends to still be underground, between food stores and special galleries they excavate to take compacted waste. Interestingly, Professor Xavier Lambin of Aberdeen’s zoology department speculates that these galleries, full of droppings and food scraps, might also be a way of generating extra heat. Derek Gow, specialist in water vole ecology, points out that an additional method of controlling temperature during the colder months is the plugging of some burrow entrances using a mixture of mud and vegetation.
So the general strategy is one of hunkering down. Although individual voles may make brief forays to the surface to nab a few greens, especially if there’s a covering of snow under which to hide, they won’t be leaving the field signs that punctuate the banks during the spring and summer.
(Thanks to Kate Long for writing this article)