Still searching for Micromouse

We have conducted 3 consecutive seasons of mammal surveying now, targeting Harvest Mice for the Surrey Mammal Group genetics study. I can only describe the feeling as 'incredibly disappointed' when you do finally capture one of your target species, then it perishes on the survey.

Eurasian Harvest Mouse (Micromys minutus), deceased adult male

Ecological surveys help us to target our conservation efforts, providing important data for reports such as the State of Nature. We do not wish to put animals through undue stress, and it was unclear why this individual died in the Longworth trap. As per the best practice protocols, traps were generously stocked with bedding, food, sources of moisture and checked within the regulated times. Harvest Mice do however have very short life spans, so it could be this individual was just reaching the end of his natural life. 

And so, after this one and only capture of a micro-mouse plus several discussions with other Harvest Mouse surveyors, these are the things I have learned:

1. Harvest Mice are difficult to survey, despite finding plenty of nests on our site. The fluctuating weather, changing habitat use and population crashes could all be impacting on our struggle to catch these little critters.

2. Despite this unfortunate mortality, Harvest Mice are fairly resilient; after speaking with other surveyors it seems very few casualties occur with Longworth traps. The overnight temperatures were above the minimum recommended for surveys, so cold was unlikely to be a factor, but we still took the precaution of providing extra insulation for the traps.

Longworth trap on stand with bubble wrap plus layers of grass

3. Wood Mice are relentless. I've seen more Wood Mice this year than craneflies. Their adaptability and climbing skills are to be commended, and they are certainly not deterred by the experience of temporary captivity! In fact, they mostly seem to find the traps before the other mammals can get a look in...

4. Shrews are awesome and sometimes I wish we were studying Shrews instead.

Lucy Groves, keeper at British Wildlife Centre with a Pygmy Shrew

Shrews love these castors (fly pupae)

5. Tube traps are a faff and take about 3 times longer to clean than Longworth traps.

6. On this survey, the average occupancy of Longworth traps was 49.71% whereas tube traps were 42.33% 

Collating trap data

Adrian Ashley is a handy chap to know - he's both an ecologist and a bespoke jeweller! He has kindly serviced the Longworth trap mechanisms which were not working so well.

7. Traps stands can definitely help to reduce the number of Common Shrew captures, but do not deter Wood Mice one little bit!

Tom Simpson often raids the set of vampire films for us 

Traps off the ground are more likely to tempt in Harvest Mice and appeal less to Common Shrews

8. Let the record stand that Martyn Cooke has still never seen a live Harvest Mouse in the wild.

Our survey data ends up in 3 places; on the internal Gatwick database, online on iRecord (which feeds into the National Biodiversity Network Gateway), and with the Surrey and Sussex Mammal Groups. We will be discussing the merits of continuing these surveys and any new approaches we might take next year.

Below are a few of our mammal records from the past 2 weeks (photos by Martyn Cooke):

Pygmy Shrew (Sorex minutus)

Bank Vole (Myodes glareolus)

Wood Mouse (Apodemus sylvaticus)

Surprise! Not a mammal: Wren (Troglodytes troglodytes)

A huge thanks to all who have helped out these past two weeks of surveys, and to Jim, Lucy and Laurie for all your advice.

Desperately seeking Micro-mouse

Guest author: Laurie Jackson

In autumn 2012, I was walking through one of Gatwick's meadows with Rachel when my eye was drawn to something on the ground. A tiny woven nest tucked amongst recently-mown grass...

I recognised it straight away as a Harvest Mouse nest. Known rather aptly as Micromys minutus, its Latin name gives a clue to this mammal's diminutive size. Averaging 6-8g, an adult weighs about the same as one long-tailed tit (or 100 of Gatwick's Honey Bees).

   Harvest Mice inhabit a range of habitats including rough grassland, wetlands, scrub and arable margins. They spend most of their time above ground-level climbing through vegetation. It is here they build their characteristic spherical nests - using rigid stems to support or suspend them from. Stripped grass is neatly woven around these supports, forming a structure to rival any of Brunel's creations. Engineer, climber, is there no end to this tiny rodent's skills? I believe the harvest mouse may also be an illusionist…

A Gatwick Harvest Mouse - found with Surrey and Sussex Mammal Groups in 2013

Over the past year I have become more and more interested in this species. After a bit of reading, I soon found I knew more about harvest mice in Japan than I did about those in my local patch! I felt uneasy when I saw the current distribution map for Sussex; with less than 150 records, there is a lot of white space on our county map. Despite this evidence to the contrary, I believe that beneath our feet a miniature army is gathering.

I am keen to find out more about Sussex's Harvest Mice and uncover new populations. To kick this off, I recently led a field trip at Gatwick to show people how to search for signs. Autumn is the perfect time for Harvest Mouse surveys, as the vegetation dies down, making it easier to find their nests. Populations of this species fluctuate annually and I have a feeling this year will have produced a bumper crop. More mice mean more nests, and in little over an hour of searching we had found 12 nests in Gatwick's North West Zone. That's a 10% increase in records… or it would have been if our search area wasn't in the vice county of Surrey!

 Our average nest diameter was 6.25cm, at an average of 40.5cm above ground level.

The star find of the day was a disused breeding nest found by our intrepid University of Brighton students. The nest still contained green vegetation, indicating it was a new-build and that breeding had probably continued into October.

Ecology student Scott has got the hang of it...

Having read this far, your mind is surely filled with just one thought - I want to look for Harvest Mice too! I guarantee that the excitement and anticipation of searching for their nests will liven up any autumnal walk. Throw in the element of danger for those fearless surveyors rooting around in bramble patches (and perhaps a pub stop along the way), what isn't there to love about a harvest mouse survey?

For more information and to get involved with the hunt, please contact me (Laurie Jackson) through the Sussex Mammal Group Website

December Summary

 

Veteran oak tree, Land East of the Railway Line

It feels like we have packed an incredible amount into December. Winter provides us with only a short window for cracking on with habitat management and it is a race to complete these jobs before the spring wildlife starts waking up again. With the incredible amount of wet weather resulting in Gatwick's rivers and streams flooding out, this will be no mean task
   Earlier this month, conservation work started with JS Agriculture and Gatwick Greenspace Partnership working together in the North West Zone. We coppiced the willows and scrub on a grassy slope which was becoming over shaded.

Coppicing willows on the grassy slope

Gatwick's ranger Tom S then improvised by staking the cut wood into habitat piles half-way up the slope, providing cover for wee beasties but leaving the wet grassland clear of debris at the bottom.

Scott finishing up our hibernacula in the Scrub West of Brockley Wood

More recently, Scott T did a grand job of moving some logs and tree stumps onto the new hibernacula in Scrub West of Brockley Wood. Sometimes I wish I could be trained to use a digger, but then with great power comes great responsibility and I can get a little power hungry.

Another completed hibernaculum - not pretty but perfect for invertebrates, reptiles and other wildlife

Our regular group of British Airways Engineers (BAE) definitely have a pact with the weatherman; on a revoltingly sunny day in mid-December, they were led by Gatwick Greenspace Partnership (GGP) on a woodland conservation task. They bridged the ditch on the main path into Brockley Wood, improving access for future work, also removing the old barbed wire, plastic tree guards and some litter. Because they can smash out these jobs in record time, I barely got any photo opportunities...

BAE installing a footbridge, East of Brockley Wood

Railway sleeper footbridge

BAE and Gatwick Greenspace Partnership

As part of the National Harvest Mouse Survey by the Mammal Society, volunteers Rachael, Sue and me carried out some nest searches along the River Mole. We had a successful haul with 4 nests on single transect along a path in the grasslands. This helps inform us where to carry out further mammal surveys in the coming year.

Well-hidden: a ball of woven grass hidden in a large tussock

A rather large Harvest Mouse nest constructed of Cock's Foot grass. 

It was probably used as a breeding nest earlier this year

While carrying out these searches, we were lucky enough to be serenaded by a very loud Water Rail. This wading bird turned up in our winter bird survey last year but eluded us on our most recent one. It still counts though as an individual record and will be added to Gatwick's species database. I think they sound a bit like excitable piglets.

Water Rail (Rallus aquaticus). The RSPB

We completed our final early winter bird survey this month in the Land East of the Railway Line. The pace has really picked up with thrushes - mixed flocks of Fieldfare, Redwing, Song Thrush, Mistle Thrush and Blackbird are abound, testing our identification skills.

Recording on our Winter Bird survey

Goat Meadow's mug-holder tree. Sadly no coffee was left in them... Mean dog walkers.

Tom F in the scrub, deep in conversation with a flock of Redwing

Looking ahead to January and February, there is an incredible amount to do and we are going to need all the volunteer help we can get. My to do list will probably keep on growing, but I seem to be running out of whiteboard...

*gulp*

Tom S is planning some conservation taster days in the New Year, so if you want to find out whether all this 'getting-back-to-nature' stuff is overrated, drop Tom a line at thomassimpson@sussexwt.org.uk or learn more here about Gatwick Greenspace Partnership and their work.

River Mole culvert, North West Zone after recent heavy rains

A massive, massive thank you to all who have been involved this past year, you have helped make this a brilliant project to work on. We hope to see you again in 2014!