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Harvest mouse

From Tilcayo Cats, the lean encyclopaedia by Tilcayo Knowledge Systems
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The harvest mouse (Micromys minutus) is the smallest British rodent. Its body is no longer than a human thumb.[1] It lives in the stalk zone of long grasses and similar tall plants.[2]

Description

The harvest mouse is orange-brown above and sharply white below. Young animals are a greyer brown. It has small, hairy ears like a vole's, a blunt nose and beady eyes. The head and body measure 5 to 8 cm, the tail is the same length again, and adults weigh 5 to 11 g. The tail is prehensile, which means it can grip, and the mouse uses it like a fifth limb when climbing stems.[1]

Nests

In summer the harvest mouse builds a ball-shaped nest of woven grass blades, 8 to 10 cm across, with an entrance at the side. The nest is usually 30 to 40 cm above the ground, sometimes more than a metre, in grass, brambles or scrub. A breeding female builds several nests in a season. They are green at first and fade to the colour of straw.[1] Winter nests are less neat and are often on the ground, for example in a tussock or a hay bale.[3]

Habitat and behaviour

Harvest mice live in many kinds of tall plant growth, including rank grassland, rushy meadows, dry reedbeds, saltmarsh, ditches, brambles and crops such as oats and wheat.[3] Yalden and Barrett also list canary grass, young forestry plantations and hedgerows.[2] The mice eat seeds, fruit, berries and invertebrates, and occasionally fungi or mosses. In summer they are active mainly at night, especially around dusk. In winter they are more active by day and live at ground level, often in the burrows of other rodents.[3]

The breeding season runs from May to October, sometimes until December. A female can have up to three litters a year, each of one to eight young. The males take no part in raising the young, which become independent at 15 to 16 days old.[4]

History in Britain

The harvest mouse was present in Britain by the Iron Age. Yalden and Barrett argue that farming from the Neolithic onwards probably created habitat for it. They say the earlier evidence is too poor to show whether it was native or introduced.[2] Harvest mice have been found in a Saxon-period collection of barn owl pellets from a floodplain.[5]

Population and conservation

Couzens and colleagues estimate a population of about 1,425,000 at the end of the breeding season, and say the species has almost certainly declined. They link this to combine harvesting and to pesticides that reduce its food.[4] Yalden and Barrett count it among the British mammals thought to number more than a million. They describe its distribution as very patchy and its colonies as often short-lived, and note that the species is easily overlooked. Changes in farming are thought to have made the countryside less suitable for it, including the switch to winter-sown wheat, which is harvested before breeding has finished, and shorter-stemmed varieties. A resurvey in 1996–97 suggested that it had declined further since the 1970s.[6] The harvest mouse does not live in Ireland.[4]

Couzens and colleagues record it on the biodiversity lists for England and Wales (see Biodiversity Action Plan), and describe it as uncommon.[1]

A newer review, published for Natural England in 2018, gives a much lower estimate of about 566,000 harvest mice in Britain, with a likely range of 288,000 to 934,000. The authors gave this figure their lowest reliability score, because numbers rise and fall a lot from year to year and harvest mice are easy to miss in surveys.[7] A guide published by Discover Wildlife, written by the Mammal Society, breaks this down as about 532,000 harvest mice in England and 34,000 in Wales, while stressing that these figures are very uncertain.[8] The review explains that the older figure of 1,425,000 (Harris and others, 1995) did not allow for the harvest mouse's smaller range, so it was probably too high. It expects the population and the amount of suitable habitat to keep falling, while the range stays about the same.[9]

On the regional Red List in that review, the harvest mouse is Near Threatened in Great Britain as a whole, Vulnerable in Wales and of Least Concern in England. Across its whole range it is of Least Concern.[10] The IUCN's European assessment, made in December 2022 and published in 2024, also lists it as Least Concern, with an unknown population trend.[11]

The harvest mouse was added to the list of UK BAP priority species after the 2007 review, for England and Wales.[12] The Mammal Society notes that it is also a species of principal importance in England and Wales under the Natural Environment and Rural Communities (NERC) Act 2006. In 2021 the society started the National Harvest Mouse Survey, in which volunteers search for nests each year to find out more about how the species is doing.[13][14]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 Couzens, Dominic; Swash, Andy; Still, Robert; Dunn, Jon (2021). Britain's Mammals: A Field Guide to the Mammals of Great Britain and Ireland (Updated ed.). Princeton University Press. p. 80. ISBN 9780691224862.
  2. ↑ 2.0 2.1 2.2 Yalden, Derek; Barrett, Priscilla (2010). The History of British Mammals. T & AD Poyser. ch. 4. ISBN 9781408128718.
  3. ↑ 3.0 3.1 3.2 Couzens, Dominic; Swash, Andy; Still, Robert; Dunn, Jon (2021). Britain's Mammals: A Field Guide to the Mammals of Great Britain and Ireland (Updated ed.). Princeton University Press. p. 81. ISBN 9780691224862.
  4. ↑ 4.0 4.1 4.2 Couzens, Dominic; Swash, Andy; Still, Robert; Dunn, Jon (2021). Britain's Mammals: A Field Guide to the Mammals of Great Britain and Ireland (Updated ed.). Princeton University Press. p. 83. ISBN 9780691224862.
  5. ↑ Yalden, Derek; Barrett, Priscilla (2010). The History of British Mammals. T & AD Poyser. ch. 5. ISBN 9781408128718.
  6. ↑ Yalden, Derek; Barrett, Priscilla (2010). The History of British Mammals. T & AD Poyser. ch. 9. ISBN 9781408128718.
  7. ↑ Mathews, Fiona; Kubasiewicz, Lisa; Gurnell, Jacqueline; Harrower, Carol; McDonald, Robbie; Shore, Richard (2018). "A Review of the Population and Conservation Status of British Mammals: Technical Summary" (PDF). Natural England. Retrieved 2 November 2026. British population estimate [566,000] (95%CI = 288,000–934,000). Reliability score = 0.
  8. ↑ Mammal Society (26 July 2021). "Harvest mouse guide: how to identify, and why its tail is unique". Discover Wildlife. BBC Wildlife / Discover Wildlife. Retrieved 2 November 2026. According to the IUCN-approved Red List of British Mammals that the Mammal Society published in 2020, there are estimated to be 532,000 in England and 34,000 in Wales, although there is a great deal of uncertainty around these estimates and a lot more research needs to be done.
  9. ↑ Mathews, Fiona; Kubasiewicz, Lisa; Gurnell, Jacqueline; Harrower, Carol; McDonald, Robbie; Shore, Richard (2018). "A Review of the Population and Conservation Status of British Mammals: Technical Summary" (PDF). Natural England. Retrieved 2 November 2026. Harris et al. (1995) estimated a British population of 1,425,000. However, this estimate is based on the ratio of harvest mice:wood mice, and is not adjusted to reflect the smaller distribution of harvest mice. The population is therefore likely to be overestimated. ... Future prospects Population status — Decline Range status — Stable Habitat status — Decline
  10. ↑ Mathews, Fiona; Kubasiewicz, Lisa; Gurnell, Jacqueline; Harrower, Carol; McDonald, Robbie; Shore, Richard (2018). "A Review of the Population and Conservation Status of British Mammals: Technical Summary" (PDF). Natural England. Retrieved 2 November 2026. Native. IUCN Red list: GB: NT; England: [LC]; Scotland: n/a; Wales: [VU]; Global: LC.
  11. ↑ Amori, G. (2024). "Micromys minutus (Europe assessment)". The IUCN Red List of Threatened Species 2024: e.T13373A221782508. IUCN. doi:10.2305/IUCN.UK.2024-2.RLTS.T13373A221782508.en. Retrieved 2 November 2026. Last assessed 22 December 2022 ... Scope of assessment Europe ... Population trend Unknown ... IUCN Red List Category and Criteria - Europe Assessment Least Concern
  12. ↑ "List of UK BAP Priority Terrestrial Mammal Species (2007)" (PDF). Joint Nature Conservation Committee. Retrieved 2 November 2026. Micromys minutus, Harvest Mouse, England Y, Scotland N, Wales Y, Northern Ireland N
  13. ↑ "Harvest Mice - On the (Road) Verge?". The Mammal Society. October 2020. Retrieved 2 November 2026. harvest mice have been identified as a Priority Species by the UK Biodiversity Action Plan (UK BAP, 2007) and a Species of Principle Importance in England and Wales (Natural Environment and Rural Communities (NERC) Act 2006, s.41-42).
  14. ↑ "Harvest mouse". The Mammal Society. Retrieved 2 November 2026. In 2021, the Mammal Society launched the National Harvest Mouse Survey - a volunteer-led annual nest survey that aims to improve understanding of the status of harvest mice across the UK.
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