Britain's smallest rodent, the harvest mouse, builds distinctive woven grass nests in tall vegetation and has declined significantly with the loss of rough grassland and traditional hedgerow management.
Harvest mice in degraded habitats with insufficient tall vegetation cannot construct the insulated breeding nests that protect young from predation and weather. Mechanisation of hedgerow cutting removes nest sites during the breeding season. The species tiny size makes it extremely vulnerable to weather extremes and predation, meaning habitat quality directly determines individual survival probability.