Understand harvest mice

Among our smallest and most beautiful mammals, harvest mice are widespread but rarely seen. To find them, search for their nests in grassy habitats in late summer and early autumn.

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Among our smallest and most beautiful mammals, harvest mice are widespread but rarely seen. To find them, search for their nests in grassy habitats in late summer and early autumn. 

  
Ecology and behaviour
 
  • The species was first discovered in the UK in the 18th century by Gilbert White, but the honour of naming it went to Peter Simon Pallas, who found the mouse in the Volga region of Russia.
  • The harvest mouse is the only British mammal with a prehensile tail tip. It’s unlikely to be native to Britain; it probably spread into western Europe in Neolithic times with the advent of farming.
  • Harvest mice are most common in south and east England, but there are scattered populations as far north as central Scotland and around the Welsh coast. They are found in any habitat with tall grasses, including roadside verges, marshlands and hedgerows.
  • The species was once associated with cereal fields, where nests and mice were seen during harvests – hence the common name. However, modern, earlier-ripening, short-stemmed cereals are no longer suitable for harvest mice.
  • Before the invention of combine harvesters, harvest mice used to be abundant in cereal ricks, and were often seen during threshing.
  • In winter, harvest mice live at ground level among dense vegetation. In summer, they spend most of their time above ground, climbing in tall grasses, hunting insects and foraging for seeds. They even live in grasses along tidal sections of saltmarshes and in tall reeds over standing water.
 
Nest-building
 
  • Harvest mice build unique nests in growing grasses. They only use living leaves, so nests are green when in use. Nests that are dead and brown will have been abandoned.
  • The mice start nest-building and breeding with new grass growth in May, but most nests are built in August and September. In mild autumns, nests continue to be built into October or even November.
  • Breeding nests are the size of a cricket ball, intricately woven and lined. Non-breeding nests are golfball-sized and less intricate.
  • When nest-building, the mouse sits on a grass stem, holding on with its tail and hindfeet, and uses its forefeet to grab nearby grass leaves, which it shreds along the length between the ribs using its incisors. The grass leaf is left attached to the stem and the free end is shredded into strips about 2mm wide.
  • After a dozen or so leaves have been shredded, the free ends are woven together to make the framework of the nest. This is then packed and lined with more leaves and down.
  • Nests are never woven around grass stems, but hang freely between them, supported by leaves attached to the stems.
  • With tussock-forming grasses (such as cock’s foot), the nest is built on top of a tussock.
  • The nest has no entrance hole; the female pushes her way in, closing the hole afterwards. At about 15 days old, the young are abandoned in the nest, which they use for another day or two.
 
Predators and mortality
 
  • Being small and unable to run fast, harvest mice are eaten by a wide range of predators. Their main anti-predator strategy is to hide in dense vegetation.
  • Skulls are frequently found in the pellets of barn owls, which hunt areas of rough grassland favoured by harvest mice.
  • Skulls are occasionally found in short-eared owl and kestrel pellets.
  • Harvest mice are also predated by stoats, weasels and pheasants. Young are even eaten by blackbirds and toads.
  • Their fine fur is good insulation against cold, but is easily soaked, making them vulnerable in wet weather. Summer downpours often kill recently emerged nestlings and even adults.

 

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