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NRNer's have found evidence of harvest mice just upstream of Eynsham Lock.

Following Bob Cowley's recent discovery of harvest mouse remains in Long Mead's barn owl's pellets, Anna Rowlands contacted harvest mouse expert Dr Amanda Lloyd to help us track down Britain's smallest and elusive rodent - the tiny acrobat of the field margins.

Barn owls have a range of between 1km and 4km, so the harvest mouse that Bob discovered in its pellet could have been a Cassingtonian or even a Freelander, rather than an Eynshamer. Therefore, confidence wasn't super high when local experts Amanda Lloyd, Anna Rowlands and Bob Cowley set off on Long Mead to survey for harvest mice, towards the end of November 

_{Anna Rowlands, Bob Cowley and Amanda Lloyd on Long Mead - image: Catriona Bass}

Britain’s smallest rodent, the harvest mouse, is relatively rare in England and is listed as “Near Threatened” in England on the UK Red List. Weighing just 4-6 grams and only 5-7 cm long, the harvest mouse (Micromys minutus) is the only British mammal with a prehensile tail, capable of wrapping around grass stems to climb like a miniature acrobat. Its soft sandy colour makes it perfectly adapted to the grassy habitats it depends on: field margins, hedgerows, reedbeds, and rough grasslands.

You would think that Long Mead would provide the perfect breeding habitat but harvest mice need a certain density of grass or reed to give protection to their nests. As we walked around the margins of Long Mead looking for nests, nothing seemed to provide that security. We went around the oxbow lake of Horseshoe Island, thinking that the reeds might provide a suitable nesting site but found no evidence there. 

Largely nocturnal and most active at dusk, the harvest mouse feeds on seeds, berries, and insects, making it an important part of farmland ecosystems. 

Status and Threats

According to the Mammal Society’s National Harvest Mouse Survey, one of the biggest problems is the lack of reliable data - no one knows how many remain, or how rapidly numbers are changing. Modern farming practices have reduced tall, tussocky vegetation and hedgerows, while pesticides and mechanical harvesting threaten their fragile nests. Habitat loss is the main driver of decline.

The Signature Nest

Unlike birds, harvest mice actually weave their nests in situ from split grasses, suspending them around 10-100cm above the ground in field margins, reedbeds, and grassy verges where the vegetation remains tall and uncut. They’re unique in Britain, making them the easiest way to detect the species.

Eventually we walked around the river margin of Long Mead, but still the grasses didn't seem dense enough. However, Amanda, using a stick to part the grasses suddenly pointed to one. 

_{Anna Rowlands showing the harvest Mouse nest on Long Mead - image: Catriona Bass}

From October to March, when vegetation dies back and nests are empty, volunteers can safely search and record them. A brown, weathered nest is usually abandoned; a fresh, green one should be left untouched.

_{Amanda Lloyd showing grasses split by the harvest mouse in anticipation of creating a nest - image: Catriona Bass}

Hope in the Margins

Every nest recorded adds to a growing national picture. The National Harvest Mouse Survey has already revealed new populations across Britain, thanks to volunteers. Continued monitoring and wildlife-friendly land management - leaving uncut margins, planting hedgerows, and maintaining tall grass - will be vital to its recovery. 

_{Harvest Mouse nest on Long Mead - image: Catriona Bass}

Now that we know that we have a local population, we will be starting regular surveys for nests in the New Year. Join our newsletter or keep an eye on our events pages for details.

(Sources: BBOWT – “Surveying Harvest Mice”, PTES – “Harvest Mouse Facts & Figures”, The Mammal Society – “National Harvest Mouse Survey”)