Record Harvest Mouse Nest Count at Woodhouse Washlands10 March, 2026 23 March, 2026 On a crisp autumn morning at Woodhouse Washlands nature reserve, volunteers slowly part the tall grasses, scanning each stem carefully. Hidden among the reeds and rushes are tiny woven spheres, delicate nests built by one of Britain’s smallest mammals. These are the homes of harvest mice. As part of our Ecological Monitoring Framework, Sheffield & Rotherham Wildlife Trust surveys harvest mouse nests at Woodhouse Washlands every three years in autumn and early winter. The survey helps us understand how the local harvest mouse population is changing over time and whether habitat management could further improve conditions for this distinctive species. The 2025 survey revealed something extraordinary. Volunteers recorded 215 harvest mouse nests, a dramatic increase compared with previous monitoring years. The remarkable nests of harvest mice The smallest rodents in Britain, harvest mice are known for their beautifully woven nests ©Anna Field Using strips of grass, they weave perfectly spherical nests in the stalk zone of vegetation, usually between 30cm and 1 metre above the ground. They create two types of nest: Non-breeding nests, about the size of a ping pong ball Breeding nests, larger and closer to the size of a tennis ball Harvest mice typically have two or three litters each year, between mid May and October. By autumn most nests are vacant and turn brown, making them easier for surveyors to spot among the vegetation. As plants die back during autumn and winter, the nests remain suspended in place because harvest mice weave living leaves and stems into their structure. What makes a good harvest mouse habitat? Harvest mice prefer dense vegetation taller than 50cm, which gives them protection from predators and plenty of nesting material. Suitable habitats include: Tussocky grasslands Field margins Hedgerows and scrub Wetlands with rushes and reeds Ditches and riverbanks Connectivity between these habitats is also important. Vegetation over 30cm high, field margins and hedgerows all help harvest mice move safely across the landscape. Woodhouse Washlands provides a mosaic of these habitats, particularly wetland areas dominated by reed canary-grass, rushes and rank grasses. Wetland habitat at woodhouse Washlands nature reserve is perfect for harvest mice. Photo ©Anna Field How we monitor harvest mice Our volunteer surveyors search for nests across a network of survey squares. These include: 50m squares across the wetland area 10m squares along the wider field perimeter The survey has been carried out three times so far as part of the EMF: YearWetland nestsField perimeter nestsTotal201924327202240141202520411215 The jump in nest numbers in 2025 is striking. Volunteers searching for harvest mouse nests ©Anna Field Where the nests are found Across all monitoring years, the majority of nests have been located within the wetland areas. Graph showing how nest counts have changed over the year, for wetland and field perimeter areas This reflects the vegetation found there. Harvest mice favour reed canary-grass, rushes and dense grasses, which provide strong stems for weaving nests. Map of nests found in 2025 Along the field perimeter, many survey squares contain shorter grassland. However, strips of taller rank grasses growing through brambles still provide pockets of suitable habitat. Pie chart showing where nests were found by habitat Why were there so many nests in 2025? Several factors may have contributed to the unusually high nest count this year. Weather conditions 2025 was a relatively dry year. This may have led to greater food availability, allowing harvest mice to successfully raise multiple litters. Reduced disturbance New fencing installed in April 2025, funded by the Species Survival Fund, reduced disturbance along parts of the field perimeter. This could explain the increase in nests detected there. Continued habitat development Wetland vegetation continues to develop and mature at Woodhouse Washlands, creating more suitable nesting habitat. Long-term monitoring will help us understand which of these factors had the greatest influence. Graph showing historic rainfall data for Sheffield 2019 – 2025 Source: Met Office historic station data for Sheffield https://www.metoffice.gov.uk/research/climate/maps-and-data The value of long-term monitoring The Woodhouse Washlands harvest mouse survey highlights the importance of consistent ecological monitoring. By repeating the survey every three years, we can track trends over time and understand how management decisions, weather patterns and habitat changes affect wildlife populations. The 2025 results are incredibly encouraging, and they would not have been possible without the dedication of our volunteer surveyors. Their work helps us ensure that Woodhouse Washlands continues to support thriving populations of harvest mice and many other species. © SSF Logo Block This project is funded by the Government’s Species Survival Fund. The fund was developed by Defra and its Arm’s-Length Bodies. It is being delivered by The National Lottery Heritage Fund in partnership with Natural England and the Environment Agency. Post navigation Older Caring for newly planted treesNewer South Yorkshire’s push for more trees