The Harvest Mouse
Where Are They Now?
1 Discovery and Context
2 Micromys - Description
3 That Wonderful Procreant Cradle
4 Where Are They Now?
5 Deaths and Entrances
6 Keeping Harvest Mice as Pets
History and pre-history.
History and pre-history.
The earliest fossil evidence of Harvest Mice is from the late Pliocene of 2-3 million years ago. They were bigger then than now and the fossil is assigned to a separate species called Micromys praeminutus. During the ice ages, there is no evidence of their presence other than in China where fossils from the Pleistocene have been found. These are of the present-day species and when the ice retreated the species spread back across Eurasia. Whether it spread into Britain before the English Channel formed is not clear however recent evidence of their presence in early postglacial deposits suggests they did. However the species is easily transported in human cargoes of hay and cereals, so it was often argued that they were accidentally introduced through trade.
The British distribution of Harvest mice is south-east of a line from the Bristol Channel to the Humber with an extension northwards into Yorkshire. In Wales where they were found for the first time on the 1970’s, they seem to be restricted to the northern and southern coastal counties. A few have been found in Scotland and those south of Edinburgh are probably natural whilst the ones to the north are probably intentional or accidental introductions.
In the rest of the world, the Harvest Mouse’s range extends in an unbroken strip across temperate Eurasia into China with outposts in SE Asia. In Europe in extends north to the Arctic Circle in Finland (but excludes the rest of Scandinavia) and southwards to northern Spain and most of Italy.
There is no reason to believe that the British distribution today is any different to what it was in the previous century but purposeful searching for their nests has shown them to be more widespread than was believed to be the case.
In south Nottinghamshire where I live, Harvest Mice are not uncommon if the presence of their breeding nests is a reliable indicator as in most years I find these within a few miles of my home when I look for them. I find them in rank grassland where this is growing up amongst stiff vegetation such as brambles, roses or thistles and sometimes against wire fences. I have developed an eye for finding the nests in field headlands, un-mown meadows, hedge-banks and track and lane verges. These are the most common sites that I find them. Once I found some in a small stand of Common reed Phragmites communis growing at the side of a brook. These habitats are scattered about my area but they exist in most parts of lowland England and Wales and along the Trent Valley, reed beds have become more extensive in the past three decades as their value to birds has become more appreciated. At Holme Pierrepont, just to the east of Nottingham, trapping studies by Nottingham University undergraduates has shown that Harvest Mice are present, not only in late summer but also (though in declining numbers) throughout the winter, thereby casting into doubt the general wisdom that Harvest Mice resort to ground-level in the winter.
Harvest Mouse sometimes use different habitats in summer and winter. They used to be common in cereal ricks when these were still built, prior to the 1950s. Sometimes hundreds of mice would be present in English ricks whilst in eastern Russia they have numbered thousands. They still enter modern barns where hay and straw are stacked and they build winter nests amongst the loose straw or wedged between bales. They very occasionally enter houses and sometimes woodland but most woods are quite unsuitable for breeding. On Studland in Dorset, they nest in the wet hollows and in winter move onto the heathland.
When the summer vegetation dies back, they are forced to cease their climbing lifestyle and descend to ground level (though perhaps not in reed beds - see above) where they build small nests for shelter amongst the vole runs and dense tussocky grasses. At this time they are in competition for food with other small mammals. Snow cover is beneficial as it seals them from the worst of the weather and hides them from many predators.
As well as the habitats already mentioned, Harvest Mice are known to use saltmarshes and sand dunes, hill meadows to 300 metres above sea level and a variety of crops, including cereals, sugar beet, potatoes, kale, clover and legumes.
They are the commonest mammal in wetland habitats because of their ability to clamber around above standing water and 31% of records come from wetland habitats including reedbeds, marshland, salt marsh and banks of rivers, stream and ditches.
I once spoke to a work colleague who said she had Harvest Mice in her garden and I pointed out that gardens were entirely unsuited to harvest mice and that they needed rank overgrown grassland growing up into brambles. She replied, “Yes. That describes my garden well!”
They have even been found in urban situations on the edge of industrial estates where things have been allowed to become weedy and wild.
The common factor is the presence of grass, sedge or rush to build their nest. 36 different species of grass have hosted them but Cocksfoot Dactylis glomerata at 27% and Reed Canary-grass Phalaris arundinacea at 18% of host species are highly favoured.
The most familiar images of Harvest Mice depict them adjacent to a nest in a crop of wheat or barley. This portrayal is based on sound observation as Gilbert White testified, but today it seems to be not at all frequent. It would be unusual to find a thistle growing in a field of wheat today. Indeed it is unusual to find anything growing in a wheat field today, other than wheat and in most cases the wheat stems are several inches apart and not heavily endowed with leaf sheathes. Also, modern varieties are much shorter stemmed than formerly. So there is little material in an intensely farmed field of cereals with which to build a nest. Furthermore, Harvest Mice have quite liberal food likings which includes invertebrates and there are not many of them in a modern field either. I think that the association with Harvest Mice and cereal crops stems from the days before insecticides and herbicides, when the seed was sown less precisely, and all in all, I think Harvest Mice would not find an intensively farmed 21st century cereal crop to their liking. Even if they did choose to build in wheat or barley they would risk being killed by combine harvester, whereas in the past, a scythe, or later a scissor cutter would have laid the stem down, nest intact and maybe given the occupants a better chance. Harvests are earlier now too - late July to early August is quite early in the Harvest Mouse’s breeding season. We can tell from Gilbert White’s letters that the harvest in Hampshire in 1767 was certainly later than August 4th and it would have been a much more prolonged affair than today’s harvests.
There was concern in the mid nineteen-fifties, when the first New Naturalist volume on mammals was published, that Harvest Mice had declined and that this was due to modern farming methods so it was almost certainly the case that people were no longer finding nests in cereal crops even in the first decades of the 20th century. Given that a cereal crop, even an untidy one with lots of weeds and insects in it, is an artificial habitat and that Harvest Mice have been present in Britain since soon after the last Ice Age i.e. before cereal crops were prevalent, the mice must have utilised natural habitats for a considerable time. Whether they completely abandoned grassy areas for cereals when the latter were favourable is not known. Whether they immediately re-occupied natural habitats when cereals became less favourable is not known either; nor will it ever be for certain, because we do not have any reliable negative reports of Harvest Mice in their modern day habitats from any time prior to 1970-75 when the first national survey was made. And by that time we know that they were occupying these natural (or more accurately, semi natural) habitats.
In other words it could be that Harvest Mice did become extremely scarce in the early part of the twentieth century but they subsequently re-adapted to the habitats that they are found in today. I suspect this was not the case however: Unless a specific search for harvest mouse nests in the late autumn and winter is undertaken it is very unlikely that they will be found. Farm workers, once familiar with Harvest Mice from their threshing days may occasionally have found them and may occasionally have known what created them, but they would be unlikely to report them to recording authorities and such instances would be isolated and infrequent. If an inquisitive naturalist in 1950, had enquired of a group of farm workers if they came upon Harvest mouse nests these days, they would most likely have replied, “No sir. We ben’t seen the little beggars since Tom Taylor were knee-high to a sparrer” Or something of the sort. And the conclusion would have been drawn that they had disappeared from the countryside.
When L Harrison Matthews wrote that,
“they seem restricted to southern and eastern counties of England but not everywhere though some places abundant………………….”
I believe he was drawing incorrect conclusions from piecemeal findings and that someone found a lot of nests one day in one place and concluded they were abundant there, whereas if they had looked again in the following season, my experience suggests they would have been forced to change their minds.
A national resurvey 1996-1997 of 800 sites where Harvest Mice had been found in 1970-1975 only located them in 20% of tetrads. This and other information led to the Harvest Mouse being made a Biodiversity Action Plan species in 2006. My own experience suggests that they are not threatened.