Harvest mice are Britain's smallest rodent and the only British mammal that builds a spherical nest woven into grass stems. Their welfare and conservation is tied to tall grass habitats that are disappearing from the agricultural landscape.
Harvest mouse welfare is shaped primarily by habitat availability and the agricultural calendar. Individual mice caught in silage cuts experience traumatic deaths; nests destroyed with young inside result in slow mortality from exposure and starvation. The progressive loss of rough grass margins, hedgerow bases, and reed beds from the agricultural landscape has reduced the availability of suitable nesting habitat, forcing mice into suboptimal habitats with higher predation risk and less thermal protection. The species' small size makes it highly vulnerable to temperature extremes, and the loss of insulating grass cover in degraded habitats increases metabolic stress during cold periods.