You are unlikely to see one , but there is a colony of the tiny harvest mouse living on Mutter’s Moor. These agile acrobats are often pictured climbing an ear of wheat with their tail coiled round the stalk, but most of them live in areas of long grass. The local population build their nests in the large tussocks of the tough Purple Moor Grass that cover parts of the moor.
At 5-7cm and weighing about the same as a 2p coin, the harvest mouse is our smallest rodent and second smallest mammal after the Pygmy Shrew. Apart from their size, they can be distinguished from other mice by their hairy ears and reddish colour of the adult fur, but mainly by their remarkable tails which are nearly as long as the rest of the body. Harvest mice have prehensile tails that can act as a fifth limb as they climb among the tall grass looking for food and building their nests.
You are very unlikely to see a harvest mouse on Mutter’s Moor because they can hear your footsteps from as far as 7m away and they will drop down into the deep vegetation long before you get near to them. We know they are living there because of their nests. When a female is due to give birth she will weave some of the grass blades into a round breeding nest just bigger than a tennis ball about 30cm above the ground but still deep inside the tussock. The nest is woven around the stiffer grass stems to hold it above the wet ground.
A female will often build more than one breeding nest, perhaps as a safety feature in case the brood nest is threatened, in which case the female will move the babies elsewhere. They make slightly smaller sleeping nests when they are not breeding.
On average, harvest mice live for about 12-15 months and will have two or three broods of 6-8 young in a summer. The pups are less than a gram when born but an eight gram mother carrying 8 pups is nearly double her usual weight. The tiny pups grow very quickly and are independent after two weeks.
Their secretive nature makes estimating the population difficult. The best estimates are that there are about one and a half million mice across the country at the end of the summer breeding season. This is probably far fewer than were around fifty years ago. Harvest mice do not hibernate and, if food is scarce because of a cold wet winter, will see their population drop by more than a half before they begin breeding again in the spring.
We know about the harvest mice on Mutter’s Moor because it is one of the sites monitored regularly by the Devon Mammal Group with help from the land managers of the Pebblebed Heaths Trust. The Mammal Group have several survey sites they will be visiting between now and March. If you would like to join them you can find out more at https://devonharvestmouseproject.edublogs.org/.
Image credits: Sarah Butcher