Harvest mouse on seedhead

In search of harvest mice again… and again… and again

For my British Animal Challenge I am trying to see every species of mammal, reptile and amphibian living in the wild. For some that’s been fairly straightforward – a case of going to the right place at the right time. Others have been more elusive. My focus this month has been on two of the trickier subjects: harvest mice and water shrews (more on the latter in my next post).

Harvest mice live up to their scientific name: micromys minutus. They are tiny. As their common name suggests, they like living among crops (grains) or areas of tall, seedbearing grasses. This makes spotting them while out and about unlikely.

Harvest mouse on seedhead

Helping out with some scientific harvest mouse trapping projects was likely to be my best chance to see them. So last autumn I volunteered to help with harvest mouse surveying at Gatwick airport. While it was a fascinating experience, we didn’t find any harvest mice. Undeterred, I volunteered for a session this year at Gatwick (work has been pretty intense lately, so I could only get to one).

Once again I got to drive through 10ft high gates topped with barbed wire, past the intimidating signs saying authorised vehicles only, before leaving the car in the glow of the runway lights, and heading off into the mini wilderness just a few hundred metres from the runway, by the River Mole. I was helping out Gatwick’s resident ecologist, Rachel Bicker (they do a surprising amount of biodiversity work at the airport). Like last year, we didn’t find any harvest mice, although we did have a good crop of voles, shrews and woodmice.

Surrey Mammal Group (working with Surrey Wildlife Trust) have been busy on a new harvest mouse project this autumn. They’re working with geneticists to see if hair samples from harvest mice can tell us about connectivity across the landscape. How related are populations in different sites to each other? Are they isolated by habitat fragmentation, or are they able to disperse and mix? This is important for the resilience of the population. And if harvest mice can move between sites, other animals will be able to as well.

Of course, to test this we first need to get samples from harvest mice. Last year the mammal group did a lot of work surveying various sites for harvest mice, and, while they were at it, tested 3 different trap designs. Based on these findings, they selected the sites with the most harvest mice last year to resurvey this year to get the samples, starting with the most harvest mousey site.

Frustratingly, work commitments meant I couldn’t get along to any of the checks at the first site, and I was ill for the week of the second site. I was restricted to seeing the updates on Facebook. The weeks progressed with plenty of voles and shrews (including my nemesis, the water shrew), but not a single harvest mouse. The dedicated volunteers consoled themselves by collecting mouse, vole and shrew poo for students to analyse for parasites.

I was finally able to help for the last check on the third site. Once again, it was the same story, the harvest mice from last year seemed to have disappeared, leaving only voles, woodmice, shrews. It was an interesting and pleasant way to spend the Friday evening, after a stressful week at work, but did leave me wondering what’s happened to the Surrey harvest mouse population.

The next site I volunteered at was by the River Wey, where I used to walk during my student days. I’d never thought about the wildlife that might live in that meadow, but looking at it now, it seems like ideal habitat for small mammals. The news from Facebook was encouraging – the group had finally caught some harvest mice, and got enough samples to analyse the population at that site, at least. Was it the night I would finally see a harvest mouse in the wild?

Harvest mouse site by the River Wey
Harvest mouse site by the River Wey

There are two moments of suspense in checking the Longworth traps. Firstly looking to see if it’s been triggered, and then, once you’ve opened the trap in a bag, waiting to see what will emerge.

Checking a longworth trap
Checking a longworth trap

We hit gold with the first triggered trap we found that evening: a harvest mouse. They are tiny. And lovely. This particular mouse had already been caught, fur clipped and sampled earlier in the week, so we didn’t need to weigh or take a sample from him again.

A not very good photo of the harvest mouse we found
A not very good photo of the harvest mouse we found

In total we had 10 small mammals in traps that night, but only one harvest mouse. Still, I had finally done it: I had seen one of Britain’s smallest and cutest mammals in the wild for the first time.

The surveys are continuing for another week or two, and hopefully we will get enough samples from other sites to compare. It will be interesting to hear the results from the lab. And hopefully it will help us find out more about habitat connectivity in Surrey. If this approach works it may help other parts of the country monitor their living landscape.

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