National Mammal Week 2021 Blog Series - Wednesday 27 October
Coordinating Harvest Mouse Surveys in Devon
Sarah Butcher
Twitter - @_sarahbutcher and @HarvestmiceDVN
Sarah is the harvest mouse project officer for Devon Mammal Group; amongst other things running training sessions, talks, surveys, writing newsletters and collating records. She has an interest in biological recording, and can often be found exploring with a camera in her hand. She is also the chair of Devon Bat Group and teaches several days a week. The project has a Facebook page and Twitter presence, both on @HarvestmiceDVN and she can be contacted on harvestmouse@devonmammalgroup.org.
Searching for harvest mice nests is addictive, so you might want to look away now! Somewhere, hopefully in a patch of grass near you, is a small tightly woven nest made exclusively of shredded grass about the size of a tennis ball. This is the breeding nest of a harvest mouse. Tightly woven into the vertical stems of grasses such as cocksfoot, they start off green and fade to straw coloured as the nests age and the babies leave. Finding one is like discovering a little piece of gold hidden in the long grass: if you haven’t found one when you’re out nest searching then you are itching to. Once you have found one, you want to find out how many more you can find! No longer can I walk past a nice patch of long grass without wanting to dive in and have a look, just in case. I often catch myself assessing the likelihood of nests as I sit in traffic jams looking at verges, but the best moments of all come as people I’ve trained (or who have attended a talk) describe the same feeling, that’s when I know I have done a good job.
I’m the harvest mouse project officer for Devon Mammal Group, running a small but far-reaching project (Devon covers a large area!) trying to comb the county looking for harvest mice. While doing so, we are contributing to the national Mammal Society harvest mouse survey, and I sit on the steering group for this. Devon Mammal Group is one of the few to already have a long term harvest mouse survey, and we’re now in our 6th year recording nests across the county. We run the project between October and March every year so that actively breeding mice are not disturbed, and have been funded by a mix of generous donations, grants and membership. The project is multi-faceted, with training sessions teaching people about harvest mouse ecology, group surveys, a newsletter about latest finds and maps updated with the latest records sent in by surveyors, now with a readership of over 350 people. We also have a trail-cam project and are hoping to start looking at owl pellets to see if they can offer more clues. You don’t have to be in Devon though to take part: the new national project is open to everyone, and somewhere near you there will be a coordinator who can help signpost you to training and suitable places to look. You can find out more by looking at https://www.mammal.org.uk/science-research/harvest-mouse-project/ and there are different ways you can join in. You can also express an interest in taking part by clicking on the links. My favourite way to take part is the really useful (and free) Mammal Mapper app. You simply open the app as you go for a walk, looking for nests as you go and taking photos that can help with verification: just make sure your battery is fully charged before you go. This information (nest type, plant species etc) then feeds into the survey, complete with accurate GPS positions. You can however fill in and send paper/email records if you would rather.
Harvest mice themselves are incredibly hard to spot, and disappear at the approach of people or predators, so we look for nests as they can’t run away. A couple of times during surveys I have seen a gingery streak shoot out from behind a tussock or into a hedge, but that’s a rare occurrence. Finding a nest fortunately happens far more often and is evidence of their presence, although it doesn’t help us know how many there are around because females often build several nests before having their babies, with litters of varying sizes. Harvest mice in Devon seem to favour slightly different habitats than elsewhere, sometimes turning up in surprising places, and we’ve even had records from parks in Exeter city centre. The majority of Devon nests though turn up in tussocks of cocksfoot grass, closely followed by molinia, of which we have plenty on the moors and commons. Harvest mice also seem to like phragmites on the edges of marshes, and with so many beautiful estuaries locally they are spoiled for choice. It seems that they also rather like the reed beds in sewage works too: they may not be the most inviting of places to search, but a recent nest search with South West Water on the edge of Dartmoor turned up eight nests along just one edge of their reed bed. The surrounding hectad had been searched many times with no record of nests, so this was a particularly exciting find. Elsewhere across the country harvest mice might favour slightly different places, such as arable crops, which are far less common here, and if you look at the webpages mentioned above you’ll see photos of suitable habitat where people have already looked and found nests to give you ideas of places to look.
As I write we’re heading to the middle of October and the harvest mouse season is just about getting underway. We already have nine nests recorded across Devon in five different places, and had our first group survey on Saturday. We had a stunning day for it, with people peeling off layers rather than putting them on. We were checking a usually reliable place for nests, and although it was a bit disappointing not to find any this time, being there as a group maximised our chances of success. We may not have found any nests, but everyone had a good walk in stunning habitat and virtually everyone has already signed up for the next survey in ten days’ time. We were even treated to Dartford warblers singing as we hunted, with brief views as we headed back to the car park. The good thing about group surveys is that if we just one person finds a nest it becomes worth it for everyone. If we aren’t lucky (only ever happened twice!) then we know it’s not that we’re not doing it properly and no one goes home dejected. The best days though are the ones where the competition starts up and people start competing to find the most nests: before you know it everyone has the bug…
I think my best tips would be not to look in one place for too long (if you haven’t found them in an hour you probably won’t and there is the danger of going the grassy version of snow-blind) and to record any nil results as it is still really useful information. I worry that lots of people think they must be doing something wrong so don’t send in a nil result, when actually this is really useful to know about. My final tip would be not to get dejected if you don’t find anything: I can go for several surveys and still not find anything, then the next time you go out you find that little bundle of woven gold and the addiction starts all over again.
Watch Sarah's How to Find Harvest Mouse Nests video below:
To find out more about what's going on during National Mammal Week 2021 click here.
