Micro-mouse micro-management

Volunteers Peter and Mark setting up humane Longworth traps

Because we are gluttons for punishment, we decided to have another crack at monitoring Gatwick's resident Harvest Mice (Micromys minutus) in the North West Zone. Again, after a week of full-on surveying, with the finest smorgasbord ever presented (Braeburn apples, Scottish porridge oats, mealworms, casters, capped off with crunchy peanut butter) catering for even the fussiest of Harvest Mouse guests... we glimpsed not even a whisker!

River Mole floodplain grasslands, North West Zone

However, it is still a great excuse to delve into the world of Gatwick's other small mammals species. Here are a few snaps depicting our finds:

Bagging and weighing occupants

Common Shrew (Sorex araneus)

Common Shrew (Sorex araneus)

Pygmy Shrew (Sorex minutus)

Re-baiting the traps after the evening check

Wood Mouse (Apodemus sylvaticus)

Wood Mouse (Apodemus sylvaticus)

To big to fit in our Longworths: Roe Deer (Capreolus capreolus)

Field Vole (Microtus agrestis)

Field Vole (Microtus agrestis)

The results of our camera trap efforts:

 Border Force Patrol Dog (Canis lupus familiaris)

Back-end of a Badger (Meles meles)

Eye-shine of a Rabbit (Oryctolagus cuniculus)

Ecologist (Homo sapiens sapiens)

NWZ Mammal survey species list 2015 (in rough size order):

• Human
• Roe Deer
• Domestic dog
• Badger
• Red Fox
• Rabbit
• Field Vole
• Wood Mouse
• Common Shrew
• Pygmy Shrew

Missing from this year's survey but recorded here previously:

• Bank Vole
• Yellow-necked Mouse
• Harvest Mouse

Harvest Mouse (Micromys minutus), North West Zone in 2013

Many thanks to all of those who helped out on this year's survey: Brad, Martyn, Anna, Adrian, Peter, Sue, Mark, Jim, Annabelle, Kathryn, Emily and both the Surrey and Sussex Mammal Groups.

Micro-mouse mysteries

I have been fortunate enough to meet some really passionate conservationists through the Wildlife Trusts, who remind me the most essential part of any scientific study is to define the question which needs answering. 

North West Zone at Gatwick, adjacent to the River Mole grasslands

Subject mammal: orangey fur, big ol' eyes, small ears and a prehensile tail

The Harvest Mouse (Micromys minutus) is a rather iconic, yet understudied mammal in our fair isles, so folk like Jim Jones and Laurie Jackson are working to fill the gaps in our knowledge. We know that Harvest Mice are present at the airport, but how well are they doing and what are their habits once autumn rolls in and the wetland water levels rise? Earlier this month, Jim and myself oversaw a survey in the North West Zone, tying into a larger population study by the Surrey Mammal Group.

Monday Evening: Setting up on site

Jim mixes up a tasty snack for our small mammal traps
(peanut butter, apple, oats and mealworms)

The aim is to compare the effectiveness of 3 types of humane mammal traps at different heights in the vegetation. This could help inform conservationists of the best way to target sample Harvest Mouse populations.

Longworth Trap on a stand

Sherman Trap on a stand

  

Trip Trap (which doesn't always trigger, meaning free food and accommodation for luckier beasties)



And did we find what we were looking for? Here is a photo diary of our results...

Day 1:

6.30am. Cool and misty morning along the River Mole, north-west of the airfield

Trainees arrive on site and Jim gives us a brief on the methodology

Our first capture is a young Field Vole (Microtus agrestis), gently scruffed to determine the gender

Noon session: a less-than-amused Wren (Troglodytes troglodytes) popped out of a longworth trap, none the worse for wear!

Evening session: 6.30pm

Persistently cute; same Field Vole (Microtus agrestis) gets emptied out for the 3rd time today

Peak Counts:

Field Vole (Microtus agrestis) x 2

Wood Mouse (Apodemus sylvaticus) x 3

Wren (Troglodytes troglodytes) x 1

Day 2:

Wood Mouse (Apodemus sylvaticus)

Yellow-necked Mouse (Apodemus falvicollis), a larger, longer-toothed cousin of the Wood Mouse

Peter bravely demonstrates how to scruff a Yellow-necked Mouse

Peak counts:

Bank Vole (Myodes glareolus) x 2

Wood Mouse (Apodemus sylvaticus) x 8

Yellow-necked Mouse (Apodemus flavicollis) x 1

Day 3:

We don't normally trap in persistently cold conditions due to welfare issues, but last night's temperature dropped to a frostier level than expected. Luckily no casualties, plus many of the traps were frozen open with all the bait snaffled (but plenty of rodent poop left in return).

Survey form

Noon session: Joe and Megan photograph the contents of a trap...

Which turns out to be our first Common Shrew (Sorex araneus)

...Still no sign of that evasive Micro-mouse!

Peak Counts:

Bank Vole (Myodes glareolus) x 2

Field Vole (Microtus agrestis) x 1

Wood Mouse (Apodemus sylvaticus) x 3

Yellow-necked Mouse (Apodemus flavicollis) x 1

Common Shrew (Sorex araneus) x 1

Day 4:

Kathryn and Sue helping to replenish bait in the traps

Evening session: Trip-trap; resolutely empty

Bank Vole (Myodes glareolus)

Peak Counts:

Bank Vole (Myodes glareolus) x 2

Field Vole (Microtus agrestis) x 2

Wood Mouse (Apodemus sylvaticus) x 6

Yellow-necked Mouse (Apodemus flavicollis) x 2

Day 5: Final morning

A relatively peaceful moment at the airport, reminds me of the film 'Warm Bodies'!

Jim holds the final Field Vole

Final Field Vole is having trouble letting go... 

(perhaps after being spoiled by days of free full-board accommodation)

Peak Counts:

Bank Vole (Myodes glareolus) x 1

Field Vole (Microtus agrestis) x 2

Wood Mouse (Apodemus sylvaticus) x 1

Yellow-necked Mouse (Apodemus flavicollis) x 3

Apparently, Harvest Mice will take their holidays around this time of year while the rest of us are still working hard. Who knows why we didn't find any, but judging from the number of nests we have seen on this site, 2015 will be be the year!

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