National Mammal Week 2020 Day 1: Grasslands
Founder of Staffordshire Mammal Group and leading Mammal Society member Derek Crawley talks about one of Britain’s smallest mammals….
The chances of actually seeing this small rodent are slim unless you are using small mammal traps and even then it’s an exciting time when the door’s closed and you think it’s empty but then suddenly there’s a movement in the bag and amongst the bedding is the golden (russet) fur of the 7g harvest mouse! That’s the same weight as a 2 pence piece.
The Harvest Mouse is primarily found in tall grasses whose stems grow close together, (reed canary grass) or in tussock grasses (cocks foot) where they make breeding nests out of living leaves woven together about the size of a tennis ball – you can even see other shredded bits of grass nearby which have not been incorporated into the nest. Harvest mice have up to 7 litters a year, each one having a new natal nest built. Males build a single occupancy nest which is about the size of a golf ball. Harvest mice do not hibernate and use single occupancy nests normally found at ground level at the base of tussocks or in the leaf litter, but these are hard to find.
Harvest mouse nest
Nest with shredding near nest site
Due to the lack of records it was thought that they were in decline, but a lack of records does not mean they are not there. Ever since I started to watch and study mammals I have looked for harvest mice and so came to the conclusion that they were rare, but on hearing about the Sorby Mammal Groups’ annual harvest mouse survey, I went along and was taught how to carry out an abandoned nest survey. The next weekend I lead the Staffordshire Mammal Group on a survey in a National Nature Reserve and we found 10 nests! These where the first ever recorded harvest mice on the site. Once people get their eye in then harvest mice nests are found across the country, with good distributions being recorded in Staffordshire, Essex, Kent, Suffolk, Devon and Berkshire. There have never been many records from Scotland but recently a nest was found on the north west coast so is this an isolated population or do we need to look harder across Scotland (as they have been found just across the border into England)?
The best way to find old nests is soon after they have stopped using them. October to January is best (before the winter storms flatten the tall grasses or destroy the nests) although you can find them throughout the winter. A fingertip search though grass stems is required; although care must be taken if bramble or nettles are present. Working in small groups is more fun than on your own, as it leads to competition – who finds the nests and how many! Each new discovery helps in finding the next as you record the type of vegetation the nest was in and what surrounded it. Anything that helps to hold the stems vertical seems to be favoured whether it be bramble, young trees or a wire fence. I like to use the Mammal Mapper app as it shows the route taken and where the nests are in relation to each other, plus evidence of field voles and other mammals can be added.
Now is the time to get out and find your first nest for the year and share your findings during Mammal Week, good luck with the searching!
How Can You Help?
To see whether a there’s a local group near you who might be conducting harvest mouse surveys click here You can also record your harvest mouse signs and sightings on our Mammal Mapper App. Find out more about this free app and how to download it here. You can read more about the harvest mouse on our Mammal Species Hub page here.