Harvest Mice

By Charlotte Owen

WildCall Officer

Hidden amongst the tall grass a foot or two above the ground, there is a carefully-woven grassy nest; an almost perfect sphere about the size of an orange and tightly anchored to the surrounding stilt-like stems. It lacks an obvious entrance but a tiny whiskered nose pushes through to nudge open a tiny doorway. A harvest mouse, Micromys minutus: the ‘smallest tiny mouse’. Tucked up inside on a bed of thistledown, completely out of view, are some even smaller, tinier mice. Adults are the length of your thumb and the weight of a 20p coin, and newborns are truly minute.

They are older now and their mother is venturing out to forage. She is well-suited to high-rise living with a prehensile tail that can grip stems like a fifth limb, aiding balance and providing a lifeline in case of lost footing. She climbs nimbly through the stalk zone in search of insects and grass seeds, including cultivated cereals like wheat and barley.It was the pioneering naturalist Gilbert White who first associated the species with the harvest, and the name stuck. During his time they were a common sight in the late summer hayricks but today there are far fewer meadows, so far fewer mice. They still cling on in agricultural fields, grassy hedgerows, bramble patches and reedbeds but seeing one in the wild is like looking for a needle in a haystack, and the harvest mouse is now listed as a Priority Species of conservation concern.

Apart from being scarce, harvest mice are deliberately elusive. They must avoid a host of predators from foxes to pheasants, all keen for a bite-size snack, and rely on super-sensitive hearing to detect the slightest rustle from up to seven metres away - equivalent to a human hearing a twig snap from 200 paces. In response, they will freeze or drop to the ground and disappear. The only traces left behind are the used nests, revealed as the grass dies down in autumn, each one with a tiny exit hole to mark the emergence of the next generation.