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.

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.

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

October Summary

River Mole grasslands

The hysteria breaking out over the False Widow Spider was like watching the inevitable conveyor-belt-of-death scene in a Bond movie. Not everyone can be expected to know about individual spider species, but when something supposedly concerns public health then journalism should be better researched, factual and responsible. This very exaggerated and misleading press was damaging to arachnophobes and spiders alike! The truth about these False Widows is that they can nip, but then so do ants, bees, wasps and household pets. This article from Buglife concisely puts the record straight: Falsehoods about False Widows.
   Spiders play an important role in our ecosystems by keeping other invertebrates in check. Only since attempting to identify some out in the field, have I come to really appreciate the beauty and diversity in their colour, patterning and textures. I believe that the tabloids should be made to apologise to all UK spiders in person.

Walnut Orb-Weaver (Nuctenea umbratica), bedded down in the moss of a dormouse box

In more local news, Gatwick Greenspace Partnership (GGP) have a new team member in the form of Tom Simpson - a skilled countryside ranger and volunteer co-ordinator. This is fantastic news for our habitat management plan as there is a lot to be done and Tom is already on the case! He joins the GGP team consisting of Pete, Kev and Tom Forward who are based over at Tilgate in Crawley.

Tom Simpson - Assistant People and Wildlife Officer

This month has been the biggest so far in terms of our habitat management, with coppicing works on the River Mole in the North West Zone and thinning the young woodland in the Land East of the Railway Line. GGP led two departments from the airport, picking up the work at Goat Meadow which had been started several years ago; it is great to see it back underway. Two teams - BT Openreach and the BDO of City Place - were led by West Sussex County Council Volunteering, focusing on opening up the ride into Upper Picketts Wood and creating a dead-hedge. This makes a real difference through creating structural diversity, allowing more light to hit the ground and increasing the floral diversity. A massive thank you to all!

BT Openreach team building - Ashley's Field

GAL Planning and Development Team - Goat Meadow

GAL Communications Team and Corporate Sustainability and Affairs - Goat Meadow

Dead-hedge running along the footpath at Upper Picketts Wood, creating

 shelter for a variety of invertebrates, small mammals and birds

BDO Tax Team - Upper Picketts Wood

Recently, while collecting invertebrates from our Malaise trap, a local couple stopped to chat to me and were carrying with them this awesome gadget... a remote control helicopter with GPS tracker and high resolution camera mounted underneath for taking low-height aerial photos, picking up all the detail in the landscape. This could make my job somewhat easier! I want one.

Helicamera, aka my Ecology Drone

And finally... after discovering a population of Harvest Mice in the North West Zone, we will be carrying out nest searches and contributing to a study by the Sussex Mammal Group. Also, looking ahead to November we have a Fungi survey (not foraging for the cooking pot, but instead learning about the diversity of species) and a Winter Thrushes survey, supporting research by the British Trust for Ornithology. Seeing the Fieldfares and Redwings arriving will be a welcome reminder that life is still out there in the colder darker seasons.

Juvenile Harvest Mouse - River Mole Grasslands

Searching for the Micro-mouse

...can be the proverbial needle in a haystack. When managing a particular habitat, we need to bear in mind which species might be occurring there. Last year, while surveying grasslands in the North West Zone with ecologist Laurie Jackson, we came across a tiny nest.

It looked rather typical of Europe's smallest rodent: a Harvest Mouse (Micromys minutus). This then got Laurie to thinking!

Somewhere, out there, deep in the River Mole grasslands... 

Harvest Mice are listed as a Biodiversity Action Plan (BAP) species because their habitats are being reduced and populations almost certainly declining. Jim Jones and his colleagues at the Surrey Wildlife Trust are conducting a Harvest Mouse Project to boost the ecological data on these often overlooked rodents. Laurie Jackson belongs to the Sussex Mammal Group and, as Gatwick is on the boundary of two counties, I was fortunate to have two pros involved in Gatwick's first small mammal survey.

A Longworth mammal trap made up of two chambers; a tunnel at the front and a chamber at the back with bedding and food. Mounting it onto a stake is an idea plagiarised from the study at Thundry Meadows. 

Longworth traps are humane, weight-triggered traps, stuffed with enough hay and food (such as oats, mealworms and carrot) for an overnight mammal stay. We check them every 12 hours, meaning that the survey is rather intensive and takes some planning. As days go by, the mammals tend to acclimatise to the traps and our hit rate increases. Below are some photos from our first and pretty successful trapping sessions:

Jim and Laurie demonstrate to assistants how to carefully bag up and empty a closed trap

Our first species was this Common Shrew (Sorex araneus) 5-14g. One of the UK's smallest mammals

An adult Field Vole (Mircotus agrestis) 20-40g. Scruffing mammals is the gentlest way

 to hold them in order to determine gender and breeding condition

A juvenile Field Vole (Mircotus agrestis). At this age they can seem almost tame

Wood Mouse (Apodemus sylvaticus) 13-27g. This particular female was both lively and pregnant

Then a bonus find in the form of a juvenile Harvest Mouse (Micromys minutus)! 

Britain's smallest rodent tips the scales at around 4-6g

It was Jim who found Gatwick's first Micro-mouse on both mine and Laurie's day off, scoring 1-0 to Surrey. This of course was quite unacceptable, so another surveying effort was needed. This time we raised the traps off the ground on stakes, hoping to target the acrobatic Harvest Mice climbing up amongst the grass stalks instead of the anxious little Common Shrews.

Chumming for Harvest Mice -  a selection of porridge oats, mealworms, apple and 

peanut butter placed in each trap to hopefully generate a feeding frenzy

I didn't go as far as baiting traps with live blowfly larvae, but I did raise the game with peanut butter and apple chunks. After setting up in the morning, we hooked our first Harvest Mouse that very evening!

A glimpse of my first wild Micro-mouse

Scruffing these little mites certainly takes some skill

We trapped two different adult Harvest Mice on consecutive days, and not that it's a competition... but I do believe that makes 2-1 to Sussex! The survey came to an abrupt end as the stormy weather began to close in; on the final evening we had a very good turn out of mammologists and a rather poor turn out of small mammals.

20 longworth traps on stands, all un-triggered. You win some, you lose some

All in all the effort was very worthwhile, so we hope to have another crack at it in spring. Many thanks to Tom Simpson and Kevin from Gatwick Greenspace for their help with the trap stands, to Laurie for her precious time and sourcing equipment, to Jim for his help and good advice, and finally to Katie, Jamie, Heather, Anthony, Martyn, Row, Pete, Reka, Rachael, James and Sue for coming along to help out on a rather damp and intensive survey.

*NB: In the defence of Surrey, it was a bit weighted towards the Sussex side in terms of people. Jim has therefore demanded a rematch!