The Harvest Mouse Micromys minutus is Britain’s smallest rodent and the only British mammal with a prehensile tail. It differs from other British mice in having a blunt nose and small ears, more reminiscent of a vole, and in adults the dorsal fur is a distinctly ginger colour, contrasting with the white belly. Its small size and prehensile tail allows it to uniquely inhabit the “stalk zone” (the shoots and leaves typically of monocotyledonous plants) and its most readily noticed field sign is its nests, woven into the living leaves of the plants. Traditionally it has been associated with arable crops but it is probably originally a species of wetlands and associated habitats, and certainly in the North East almost all recent records have been from rank grassland or wetlands. In winter it becomes more terrestrial and will utilise the burrows of other small mammals or move in to stacks in barns and, very occasionally, in to other outbuildings (Harris, 1979).
In Britain it has a mainly southern and eastern distribution (Trout and Harris, 2008) where it appears not to be uncommon in the right habitat. For example, a search of likely habitats in Essex by a single surveyor confirmed their presence in 19 new tetrads in less than four hours (Dobson, 2001)! Further north its recorded distribution is patchy with Howes (1985) only having six Yorkshire records north of Northallerton though, more recently, analysis of owl pellets from 22 sites across the North York Moors between 2008 and 2014 found Harvest Mouse remains at 10 of those sites (Capes, 2015).
In the North East the species appears to have been very infrequently encountered historically. Mennell and Perkins (1864) note; “We have but few recorded localities for this species in our district, but among these, one is worthy of note from its great elevation; Mr. Wm. Backhouse has taken it at St. John’s, Weardale, 800 feet above the level of the sea” (at grid ref. NZ069339). Similarly Gill (1905) states: “The harvest mouse appears to have been very rarely noticed in the County of Durham and is doubtless scarce, though I have lately seen it myself a very short distance north of the Tyne.”
This seems to have continued to be the case in the intervening period. A handful of records have come to light from the 1960s based on the memories of farmers and gamekeepers. So far these have all been from the Tees Lowlands, roughly both north and south of Darlington, and from High Spen in the Derwent Valley, near Gateshead. Harris and Larding in their 1974 survey of Harvest Mice in Britain found only four records from the North East plus one just south of the region at Hutton Rudby (Harris, 1979). Records continued to be scarce up to 2000 with only six accepted records in the last two decades of the 20th century. These were: Lockhaugh Sewage Farm, some three km from High Spen, in 1985; Castle Eden Walkway in Stockton in 1986; Prestwick Carr, Northumberland in 1998; Boulby in south Cleveland in the 1990s; and Earsden Hill Farm, near Morpeth in 1996 and again in 1997. This last site was the same place as Harris and Lording had found the species in 1976. There is an unconfirmed record of Harvest Mouse from Ladythorne, north of Haggerston and just south of the Scottish border, from 1997. Unfortunately no further details of that record could be obtained but it is the only known claim of a record in Vice County 68 and would consequently be the most northerly record in England, if proved. Other than those associated with a re-introduction programme at East Chevington in Druridge Bay, there had been no confirmed records of Harvest Mice in Northumberland, or indeed anywhere substantially north of the Tees Lowlands, in the first decade of the 21st century.
The lack of recent records and consequent concerns that the species might be extinct in the region led to series of re-introduction attempts in the early 21st century which are detailed in Bond (2010). These occurred in the Tees Valley at Cowpen Bewley Woodland Park, Wynyard Woodland Park, Portrack Marsh and Teesmouth Brine fields with an unrelated re-introduction attempt being made in reed beds at East Chevington. Initially all attempts appeared to have failed as no Harvest Mice were found after the first few months following the releases, but subsequently Harvest Mice have been positively identified at four of the sites and are also believed to be present at the fifth, Portrack Marsh, after a period of several years.
Fears of regional extinction proved to be unfounded as subsequent attention on the species both as a Local Biodiversity Action Plan Species and through publicity associated with the re-introductions brought to light a small but increasing number of records throughout the Tees Valley. The first record of the 21st century occurred when a small number of Harvest Mice turned up in a stable at Pinchinthorpe near Guisborough in 2003. As the habitats immediately surrounding the barn were not thought suitable for Harvest Mice it was postulated that they had come in with the bedding which had come from Boozebeck about eight km further east. In the same year two records came to light near Great Ayton. While, technically, outside the region in North Yorkshire, it is just four km from Pinchinthorpe so the mice in the stable may have been from the surrounding area. The following year, the author found two Harvest Mouse nests between Darlington and Stockton and the species was also recovered from Long- eared Owl Asio otus pellets near Eaglescliffe. Further records continued to trickle in during the first decade of the century and the species was found to occur from around the Boulby area in the extreme southeast of the region, where there were records spanning two decades, as far west as the north of Darlington. Notably there were records in several separate sites between the north of Darlington and Stockton, which suggest that the species is widespread, though possibly localised, in that particular area.
Bond (2010) describes all of the known North East records, including historical and unconfirmed ones, up to 2009. At that point 16 contemporary records had come to light, all in the Tees Lowlands, including three from Great Ayton, with a further two records slightly further afield, at Seamer and Hutton Rudby. There was also an unconfirmed record from Brinkburn Priory in Northumberland.
More recently the picture of Harvest Mouse distribution in the North East has changed significantly. Initially this was through several casual records that extended the species known, current distribution, for example to the northern boundary of the borough of Hartlepool and at Bowburn, just south of Durham City. There was also an exceptional record of two small, ginger mice climbing around the top of grass stems at Slit Woods in Weardale. This is towards the extreme west of the county and around 35 km west of the closest 21st century record. It is even 16 km west of William Backhouse’s 19th century record and at an elevation of around 350 metres would be around 200 feet higher still.
This evidence that Harvest Mouse was still extant further west and north in the North East than previous records had suggested led to regional surveys for the species in 2014 and 2015. These were organised by Northumbria Mammal Group in conjunction with Durham and Tees Valley Wildlife Trusts. Over the two years, 69 surveys took place at a total of 64 separate sites and resulted in positive evidence of Harvest Mouse in 12 new locations plus confirmation of its continued presence in some of the sites where it had previously been recorded. Perhaps the most notable single record was at Langton, west of Darlington, which was the first record for Teesdale since Harris and Lording found them a few miles up the road at Little Newsham, 40 years previously (though several other surveys further up Teesdale all proved negative). The surveys found Harvest Mouse to be distributed in a band extending from the east coast, from Hartlepool, as far north as Seaham, across to the several sites south of Durham City. All sites surveyed west or north of Durham City proved negative.
Outside of the organised surveys other records have come to light, which have mainly filled in gaps in the species known distribution although two in particular have significantly extended the current limits of its north east distribution: A tiny mouse was seen clambering around the top of some Campion Silene sp. stems at Clara Vale, west of Gateshead. From the description given it seems likely that it would only have been Harvest Mouse, which moves its current distribution much further north and west in County Durham, although there are some records from the 1960s from that general area of the County. Perhaps even more significantly, Derek Crawley found nests at Big Waters, near Newcastle Airport. This is the first confirmed Northumberland record this century, other than as a result of the introduction at East Chevington.
It is now known that Harvest Mouse is widely distributed in the Tees Valley, apart from in the main Teesside conurbation. There are an increasing number of records across East Cleveland and several records between Stockton and Darlington. There is even a record from Teesside Park, where suitable habitat extends into the centre of the conurbation along the former course of the River Tees. Harvest Mice are now regularly reported around the North Tees marshes at the introduction site at Cowpen Bewley Woodland Park and at RSPB Saltholme, which is around two km from the Woodland Park. Further north they are also widely distributed in east Durham, from the coast between Seaham and Hartlepool as far west as the A167, just to the south of Durham City. Outside of these core areas there are a few very widely scattered records as far north as south Northumberland. Whether these are isolated populations or whether Harvest Mice are widely distributed in those areas requires further investigation.
Written by Ian Bond (last updated April 16)