Harvest mouse day
I'm always looking to improve my field identification skills, and expand my knowledge of British mammals. Last month (Saturday 18th November) my boyfriend Joe and I went along to the Mammal Society's first annual harvest mouse day at Doxey Marshes in Stafford. Doxey Marshes is a nature reserve characterised by rough grassland and wetland habitats, managed by the Staffordshire Wildlife Trust. At first glance, this reserve seemed an unlikely place for secretive mammals such as harvest mice (Micromys minutus), otters (Lutra lutra) and water shrews (Neomys fodiens) to inhabit since it's located right on the urban fringe, yet all three species manage to persist there.
The training course was fully booked and we were guided by Derek Crawley, the founder and chair of the Staffordshire Mammal Group since 1999. Derek was immensely knowledgable about British mammals, having been a Staffordshire Mammal Recorder since 1998, as well as a member of the Mammal Society Council since 2012.
Harvest mice habitats
To start the day, Derek gave us an introduction to harvest mouse ecology which involved showing us photos of indicative field signs and providing tips of where best to search for them. According to Derek and some online articles, harvest mice tend to live in tall, dense swards of ground vegetation (exemplified in the photo below).
Harvest mice can live in both wet and dry grassland areas as long as suitable plant species are available. The key requirements of these species are that they are stiff stemmed and have leaves that can be split lengthways in order to weave nests. In wet grassland areas (like Doxey Marshes) harvest mice favour sedges (Cyperaceae family) and grasses such as reed sweet grass (Glyceria maxima) common reed (Phragmites australis) and reed canary grass (Phalaris arundinacea). In drier areas, harvest mice may show a preference for other grass species such as cocksfoot (Dactylis glomerata).
The advantages of living in the habitats described above are varied and many; firstly, they provide the seeds, small invertebrates, nectar and fruit on which harvest mice feed; secondly, they offer shelter from arial predators and the elements; and thirdly, the long blades and stalks of plants can be used to weave nests above ground, out of the way from flood waters and ground predators.
As their name suggests, harvest mice may also be found living among cereal crops. The species was first accurately described by the naturalist Gilbert White in 1767 who found them nesting in cornfields around his village Selborne in Hampshire. White described the mice as being "abound in harvest" and wrote that they "build their nests amidst the straws of corn", hence the name harvest mouse was coined.
Natural harvest mouse habitats are increasingly hard to come by owing to their conversion into agricultural land to meet the needs of a growing human population. According to DEFRA's latest Agriculture in the United Kingdom report (2017) which uses 2016 data, 71% of the UK's land is classified as Utilised Agricultural Area (UAA), an increase of 1.2% since 2015. Of this agricultural land, 17.8% (3.1 million hectares) is cereal crop, up by 1.0% since 2015.
Owing to the decline in natural habitats and increase in agricultural land, many harvest mice have little choice other than to occupy cereal fields and their verges. Although, cereal crops (such as wheat and oats) may offer a plentiful food supply, they don't come without their risks; modern arable farming generally involves the spraying of harmful pesticides and unforgiving machinery to harvest the crops. Unfortunately for harvest mice, the harvest of many crop plants coincides with their breeding period, with the majority of litters born in August and early September.
As a result of the risks imposed by agricultural practices, it is increasingly important to leave unmown field margins and set aside land for grass-loving species such as harvest mice. Additionally, grassy hedgerows have been found to provide favourable harvest mouse nesting sites, particularly those composed of brambles (Rubus fruticosus) and thorns (Crataegus monogyna and Prunus spinosa) (Bence et al., 2003).
Harvest mice nests
Harvest mice create two kinds of in-situ nests: the summer breeding nest and the temporary winter nest. Summer breeding nests are the most readily recognisable field sign and are about the size of a tennis ball (~10 cm in diameter), comprising a hollow sphere of carefully woven plant blades which have been shredded lengthways using their front teeth and paws. These nests are located in the centre of their home range and are suspended between plant stems up to 150 cm off the ground - that's the equivalent of ~15 m heigh or the height of the Hollywood Sign in LA for humans!). Females are capable of producing between three and six litters a year, each inside a freshly built nest and comprising up to eight offspring. In contrast, temporary winter nests are considerably smaller (~ 5 cm in diameter), located closer to the ground in grass tussocks and are used for sleeping and food storage.
Owing to their highly secretive, trap shy and essentially nocturnal nature, the most reliable method of surveying for harvest mice is through nest searches; however even these are not always easy to find! It took me almost an hour to discover my first nest, however, by the end of the day we successfully managed to locate 24 nests between 13 of us - not a bad tally, considering only two people had undertaken nest searches prior to the course.
Abandoned breeding nests may be found in uncut swards of vegetation between October (however, be wary of late litters from October-December) right through to March, when spring vegetation growth makes them more difficult to find. Harvest mice appear to show nesting preferences for relatively dense stands of sedge and grass species, but not so dense as to prevent the necessary movement required for nest weaving. See below for some photos of a nest that I found at Doxey Marshes. I'd recommend wearing wellies (for the boggy patches) and gloves (so that you don't cut your hands on the grass and sedge blades).
The scientific name Micromys minutus is very apt for the harvest mouse. This 'minute micro mouse' is Europe's smallest rodent, with adults only weighing between 5 and 11 g (roughly the same weight as a 2 p coin!). The harvest mouse's light weight enables an acrobatic and lofty lifestyle amongst tall stems and blades of vegetation. The animal's exceptional climbing abilities are attributed to its broad hind feet, whose outermost toes are opposable, thus enabling good grip on plant stems. The presence of a remarkable hairless prehensile tail further aids climbing by serving as a fifth limb or safety rope by wrapping tightly around nearby stems (Sterry, 2010).
The nest-weaving of the harvest mouse is dependent on two key adaptations: the mouse's sharp incisor teeth for shredding blades of vegetation into linear strips, and the agile front feet, which enable manipulation of the blades of vegetation.
Two abandoned harvest mice summer breeding nests, which I found at Woodwalton Fen National Nature Reserve.
How you can help harvest mice
References:
Bence, S.L., Stander, K. and Griffiths, M., 2003. Habitat characteristics of harvest mouse nests on arable farmland. Agriculture, ecosystems & environment, 99(1), pp.179-186.
DEFRA, 2017. Agriculture in the United Kingdom 2016. Available at: www.gov.uk/government/statistics/agriculture-in-the-united-kingdom-2016. 17 July 2017. Accessed on: 28/12/2017.
Sterry, P., 2010. Collins Complete Guide to British Animals: A Photographic Guide to Every Common Species. 2nd ed. HarperCollins Publishers Limited, UK, pp.78.
Doxey Marshes Nature Reserve in Stafford.
The training course was fully booked and we were guided by Derek Crawley, the founder and chair of the Staffordshire Mammal Group since 1999. Derek was immensely knowledgable about British mammals, having been a Staffordshire Mammal Recorder since 1998, as well as a member of the Mammal Society Council since 2012.
Harvest mice habitats
To start the day, Derek gave us an introduction to harvest mouse ecology which involved showing us photos of indicative field signs and providing tips of where best to search for them. According to Derek and some online articles, harvest mice tend to live in tall, dense swards of ground vegetation (exemplified in the photo below).
Harvest mice can live in both wet and dry grassland areas as long as suitable plant species are available. The key requirements of these species are that they are stiff stemmed and have leaves that can be split lengthways in order to weave nests. In wet grassland areas (like Doxey Marshes) harvest mice favour sedges (Cyperaceae family) and grasses such as reed sweet grass (Glyceria maxima) common reed (Phragmites australis) and reed canary grass (Phalaris arundinacea). In drier areas, harvest mice may show a preference for other grass species such as cocksfoot (Dactylis glomerata).
Dense swards of sedge (Cyperaceae family) such as this one at Doxey Marshes make ideal habitats for breeding harvest mice. Sedge species provide stiff v-shaped blades to weave nests from as well as refuge from predators.
The advantages of living in the habitats described above are varied and many; firstly, they provide the seeds, small invertebrates, nectar and fruit on which harvest mice feed; secondly, they offer shelter from arial predators and the elements; and thirdly, the long blades and stalks of plants can be used to weave nests above ground, out of the way from flood waters and ground predators.
As their name suggests, harvest mice may also be found living among cereal crops. The species was first accurately described by the naturalist Gilbert White in 1767 who found them nesting in cornfields around his village Selborne in Hampshire. White described the mice as being "abound in harvest" and wrote that they "build their nests amidst the straws of corn", hence the name harvest mouse was coined.
An extract on harvest mice from one of Gilbert White's letters (1767) displayed in The Natural History of Selborne (1833), which was recently given to me by my grandmother Hope Thorp, and first collected by my great grandmother.
Owing to the decline in natural habitats and increase in agricultural land, many harvest mice have little choice other than to occupy cereal fields and their verges. Although, cereal crops (such as wheat and oats) may offer a plentiful food supply, they don't come without their risks; modern arable farming generally involves the spraying of harmful pesticides and unforgiving machinery to harvest the crops. Unfortunately for harvest mice, the harvest of many crop plants coincides with their breeding period, with the majority of litters born in August and early September.
As a result of the risks imposed by agricultural practices, it is increasingly important to leave unmown field margins and set aside land for grass-loving species such as harvest mice. Additionally, grassy hedgerows have been found to provide favourable harvest mouse nesting sites, particularly those composed of brambles (Rubus fruticosus) and thorns (Crataegus monogyna and Prunus spinosa) (Bence et al., 2003).
Harvest mice create two kinds of in-situ nests: the summer breeding nest and the temporary winter nest. Summer breeding nests are the most readily recognisable field sign and are about the size of a tennis ball (~10 cm in diameter), comprising a hollow sphere of carefully woven plant blades which have been shredded lengthways using their front teeth and paws. These nests are located in the centre of their home range and are suspended between plant stems up to 150 cm off the ground - that's the equivalent of ~15 m heigh or the height of the Hollywood Sign in LA for humans!). Females are capable of producing between three and six litters a year, each inside a freshly built nest and comprising up to eight offspring. In contrast, temporary winter nests are considerably smaller (~ 5 cm in diameter), located closer to the ground in grass tussocks and are used for sleeping and food storage.
Owing to their highly secretive, trap shy and essentially nocturnal nature, the most reliable method of surveying for harvest mice is through nest searches; however even these are not always easy to find! It took me almost an hour to discover my first nest, however, by the end of the day we successfully managed to locate 24 nests between 13 of us - not a bad tally, considering only two people had undertaken nest searches prior to the course.
Abandoned breeding nests may be found in uncut swards of vegetation between October (however, be wary of late litters from October-December) right through to March, when spring vegetation growth makes them more difficult to find. Harvest mice appear to show nesting preferences for relatively dense stands of sedge and grass species, but not so dense as to prevent the necessary movement required for nest weaving. See below for some photos of a nest that I found at Doxey Marshes. I'd recommend wearing wellies (for the boggy patches) and gloves (so that you don't cut your hands on the grass and sedge blades).
A harvest mouse nest predominantly made from sedge blades and found at Doxey Marshes Reserve.
Harvest mice adaptations
The scientific name Micromys minutus is very apt for the harvest mouse. This 'minute micro mouse' is Europe's smallest rodent, with adults only weighing between 5 and 11 g (roughly the same weight as a 2 p coin!). The harvest mouse's light weight enables an acrobatic and lofty lifestyle amongst tall stems and blades of vegetation. The animal's exceptional climbing abilities are attributed to its broad hind feet, whose outermost toes are opposable, thus enabling good grip on plant stems. The presence of a remarkable hairless prehensile tail further aids climbing by serving as a fifth limb or safety rope by wrapping tightly around nearby stems (Sterry, 2010).
The nest-weaving of the harvest mouse is dependent on two key adaptations: the mouse's sharp incisor teeth for shredding blades of vegetation into linear strips, and the agile front feet, which enable manipulation of the blades of vegetation.
Longworth traps
During the course of the day, we also checked a series of Longworth traps which Derek had set the night before. The Longworth is a type of metal trap with a door tripping mechanism, designed for live trapping small mammals with minimum discomfort. Derek had baited these traps using seeds and mealworms and included straw for bedding in the hope of live capturing a harvest mouse. Alas, as previously mentioned, harvest mice are particularly trap shy creatures and we failed to capture any. However, these elusive creatures were kind enough to leave some calling cards on top of an untriggered trap (see photo below).
Six harvest mice droppings on top of a Longworth trap (pound coin for scale).
Although we weren't successful in live trapping any harvest mice we did manage to live trap two bank voles (Myodes glareolus) which appeared to sit quite happily in the palm of Derek's hand. The bank vole is such a charming mammal, which I feel is often overlooked.
A bank vole found in one of the Longworth traps.
As well as harvest mice signs and bank voles, we had the pleasant surprise of seeing a Cetti's warbler (Cettia cetti), which is apparently a rare sight due to its skulking behaviour. We also found some badger latrines and otter spraints, indicating the high wildlife value of the Doxey Marshes Reserve.
Harvest mice at Woodwalton Fen
A week or so after the Mammal Society's harvest mouse training course, I thought I'd put my new nest finding skills to the test. Whilst driving along one of the flood storage reservoir banks on the edge of Woodwalton Fen National Nature Reserve, I spotted what looked like a suitable harvest mouse nesting site, dominated by sedges and grasses. Within a couple of minutes of examining a nearby sedge tussock I found two neatly crafted summer breeding nests (see photos below).
A sedge sward providing an ideal habitat for harvest mice along the perimeter of Woodwalton Fen National Nature Reserve.
Two abandoned harvest mice summer breeding nests, which I found at Woodwalton Fen National Nature Reserve.
The harvest mouse is listed as a UK Biodiversity Action Plan Priority Species since it is thought to have declined in recent years, and thus requires conservation interventions to boost its numbers. It is unclear to what extent the harvest mouse's population level has deteriorated, because as previously mentioned, its elusive behaviour makes it difficult to quantifiably survey. As a result of the limited data, it is vital that as many people as possible are trained to undertake field surveys and submit their records via citizen science biodiversity databases. A citizen science database that I'd recommend submitting your records to is the Mammal Tracker app, which is available to download from this website.
If you're interested to attend a harvest mouse day, the next one run by the Mammal Society will be on the 20th October 2018 at Doxey Marshes. Click here to find out more.
In terms of helping to conserve the harvest mouse on your own land, check out the Suffolk Wildlife Trust's conservation guidelines.
If you're interested to attend a harvest mouse day, the next one run by the Mammal Society will be on the 20th October 2018 at Doxey Marshes. Click here to find out more.
In terms of helping to conserve the harvest mouse on your own land, check out the Suffolk Wildlife Trust's conservation guidelines.
And finally, to end on a positive note, you may like to read about some harvest mouse conservation efforts involving the recycling of 36,000 Wimbledon tennis balls in order to create artificial nests. These balls were collected after the world-famous tournament in 2001 before having a small hole bored into them and being suspended by poles between 75 and 150 cm above the ground, the idea being that they would help reduce harvest mouse predation by weasels and birds of prey. Check out the article by clicking here.
References:
Bence, S.L., Stander, K. and Griffiths, M., 2003. Habitat characteristics of harvest mouse nests on arable farmland. Agriculture, ecosystems & environment, 99(1), pp.179-186.
DEFRA, 2017. Agriculture in the United Kingdom 2016. Available at: www.gov.uk/government/statistics/agriculture-in-the-united-kingdom-2016. 17 July 2017. Accessed on: 28/12/2017.
Sterry, P., 2010. Collins Complete Guide to British Animals: A Photographic Guide to Every Common Species. 2nd ed. HarperCollins Publishers Limited, UK, pp.78.
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