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Surrey Harvest Mouse Project

Report for

People’s Trust for Endangered Species

David Williams CMIEEM

January 2015

Surrey Wildlife Trust, School Lane, Pirbright, Woking, Surrey GU24 0JN

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The Harvest Mouse (Micromys minutus) project began in 2011 as a result of a successful

application for funding to People’s Trust for Endangered Species. Surrey Wildlife Trust

also part funded the project.

Although populations are reported to have declined by 71% (Sargent et al 1997) very

little successful survey work has been undertaken in Surrey. Lack of survey information

about Harvest mice numbers is probably due to the ineffectiveness of survey and trapping

techniques (Riordan et al 2009; Poulton and Turner 2009 and Meek 2011). Nest searches

can be overestimated with Harvest mice building several nests for each brood (R.C.Trout

and S.Harris, Mammals of Great Britain 2008). The project used several types of surveys

and different trapping methods.

The aims were to enhance our knowledge and status of the species (which would inform

management plans to ensure sensitively managed habitats) and raise public awareness of

the conservation status of the Harvest mouse, using them as a flagship species to promote

landscape scale conservation of floodplain grazing. These aims would be achieved by

trapping, nest surveys, owl pellet dissection, positioning hair tubes and camera traps. We

trialled three types of small mammal live traps at two different heights (one being at floor

level). Nest searches were undertaken and owl pellets were collected and dissected to

search for Harvest mice remains. Hair tubes were trialled at various heights, along with

trail cameras placed in the stork zone. Sites were chosen by using any one of three

criteria:

1) Habitat looked suitable

2) Nests had been found

3) SWT held previous records.

Volunteers were recruited before the project started and were invited to our first training

day. Twenty-five attended. Attendees learnt about the ecology of the Harvest mouse,

our trapping methods and owl pellet dissection. We also had live captive-bred Harvest

mice from The British Wildlife Centre.

The three types of trap that were used were the plastic trip-trap, the well tried and tested

Longworth trap and the small sized Sherman trap.

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All three were tested for trap efficiency by placing them in the Harvest mice enclosures at

The British Wildlife Centre. The Longworth’s trip bar had been set to trip at the lightest

possible weight, as the harvest mouse is the lightest of our small mammals. All three

types of trap were tripped when an animal entered to eat the bait.

Hair tubes were also trialled to find out the minimum size required to trap hairs from the

small Harvest mouse. This proved difficult but eventually a hair was caught in a tube

whilst it was in a cage. Hair tubes had to be 20mm internal diameter. Hairs for

comparison were taken from these captive-bred animals.

The project used 20 of each type of trap at the two different heights; these were placed

close together to maintain as similar habitat as possible for each group, which was

labelled as a station. This gave us 6 traps at each station and ten stations at each site.

Thirty stakes were made so that the above-ground traps could be placed at as near to

600mm as possible. Stations were placed at 15-20 metres apart depending on the habitat.

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Traps were set up on Monday evening and then checked and re-set and re-baited at 0630

the following morning; a further check followed at 1230 and again at 1830. This gave us

three sampling sessions per day; this continued for 5 days, with the last check taking

place on Saturday morning when the traps and posts were removed. Bait type was

selected and used throughout the whole project. This consisted of a bird seed mixture,

with castors added to ensure any Shrews had food for survival, and a small piece of apple

to provide moisture for trapped animals. This proved difficult in Sherman traps as the

seed would easily slide under the trip mechanism and stop the trap from closing. To

avoid this, peanut butter was used with the seed and castors, mixed in to make a paste to

stick to the back plate and avoid spillage under the trap door.

20 sites were trapped with 12 having 60 traps and 8 having 120 traps at different

locations within the site. Two sites were re-visited (see appendix 1 for list of sites).

It was hoped that we could run two different sites concurrently however resources were

unavailable to enable us to do so. Volunteers could not be found to complete all the

checks for a full week and an additional SWT staff member was unavailable.

The first trapping session took place in August 2011. A site was chosen with recent

records of Harvest mice nests. The site was an SWT reserve and 2 sites were used with a

total of 120 traps. Although no target species were caught, it was a useful exercise to test

our equipment. Some minor adjustments were made. Trapping continued on a further

six sites before temperatures dropped (when trapping was considered to be a welfare

issue). During this first year, Harvest mice were caught at 4 sites.

Trapping was planned for the spring of 2012, but high temperatures made it a welfare

problem especially with the traps on posts getting too hot. Trapping continued in

September to November at another six sites, with Harvest mice caught at three. In 2013,

only 5 sites were completed although 3 of the sites had 120 traps. This was due to

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sickness and bad weather. Harvest mice were caught at two sites. It was decided to

continue the project for another year to gain more meaningful data. In 2014, a further 4

sites, each with two sets of traps, were undertaken. Harvest mice were trapped at all of

these sites (results table in appendix 1).

Many of the trapping sessions were completed in darkness which meant working by torch

light.

A total of 65 volunteers were used during the project, with many becoming well trained

in trapping methodology.

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Results

A total of 197 harvest mice were trapped; of these, 126 were new catches; 71 were re-

traps, identified by fur clips. The range of totals per site (where Harvest mice were

caught) was from 1 up to 46, with only 6 sites reaching double figures. Harvest mice

were caught in all types of traps and at each of the two heights. Figures show that the

most trappings by trap type and height were Longworths on the ground.

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All of the new captures were weighed and sexed and all data collected. Each new

Harvest mouse caught was fur clipped.

Average weight was 6g, with several at 12g, which were pregnant or lactating females.

Sex ratio was in favour of females at 57% .

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Harvest mice were trapped at each session morning, midday and evening, confirming that

they are active day and night. The largest numbers of Harvest mice were found at the

morning checks.

A total of 71 Harvest mice were re-trapped.

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We trapped some harvest mice in late October that showed a clear moult line.

Nest searches were made during each survey and also at other times. Nests were more

easily found where Harvest mice were trapped, but also found at sites where trapping was

unsuccessful.

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Nest searches were also undertaken at training sessions with volunteers from other

organisations: PTES, National Trust and Mammal Society.

Habitats varied: heathland, grassland areas, reedbed, flood plain and River meadows.

Reedbed site River meadow site

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Camera traps were deployed with very little success. Only three sequences of a Harvest

mouse were obtained, with many other images captured of reeds blowing, rain falling and

also a Fox (Vulpes vulpes) investigating traps.

Owl pellets were collected but we had difficulty finding them close to our sites. Pellet

dissection was part of the training days we held, so we were able to train volunteers how

to identify small mammal remains, especially Harvest mice. None were found in pellets

from our area, but pellets obtained from other areas outside Surrey had Harvest mice

remains to help with identification skills.

CAMERA TRAPPING

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Riverside, the most productive site in 2013, was heavily flooded in the 13/14 winter, with

the water completely covering the vegetation. Trapping was tried during August without

success, however in October we were very successful. Harvest mice had somehow

survived the flood. There was higher ground nearby, so it is possible they fled to higher

ground to survive, returning when the flooding subsided.

Conclusions

Hair tubes were unsuccessful and no hairs were obtained. These were trialled on captive

Harvest mice, and even then, only on one occasion did we collect a hair.

Camera traps gave us poor results despite some being aimed at nests. The speed of

which a Harvest mouse can move through the stems is possibly too fast for cameras to

trigger.

Owl pellets can be a good source of information provided they can be found in the

vicinity of the site surveyed.

Nest searches were extremely useful in deciding presence or absence on a site, but could

not be relied upon to indicate population numbers.

Sherman traps had no place for bedding, causing welfare problems in cold weather and

were difficult and time consuming to clean and re-bait. Harvest mice were captured, but

not as many as in Longworth traps.

Trip traps were successful, but had the problem of trapped animals sweating or getting

cold. Like the Sherman traps, there was no place for bedding.

Longworth traps were the most successful and by far the easiest to clean and re-bait.

Bedding improved the welfare of each trapped animal.

Position of trap favoured being at ground level, although enough were caught at stork

zone height to suggest that traps could be placed on the ground and on posts to increase

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trapping success.

Season: Results confirmed previous personal comments (R C Trout) that Harvest Mice

are more likely to be caught in autumn rather than summer. We trapped on sites that were

successful during October and November, but with no success in Summer. Results also

confirm that Harvest Mice are difficult to trap in large numbers to supply meaningful data.

Comments

The largest catch was made on Clay Lane 1, an unmanaged wet area comprising mostly

of Meadow Sweet (Filipendula ulmaria) and Broad-leaved Dock (Rumex obtusifolius).

This was an exceptionally high number of catches. The site had been lightly grazed

illegally for a few weeks in 2014, otherwise it has been untouched for many years. Clay

lane 2 on the same plot consisted of Bramble (Rubus fruitcosus agg.) and Himalayan

Balsam (Impatiens glanudifera). The owners, Guildford Borough Council, are

considering this site to be designated as part of their Riverside Nature Reserve, and will

allow any long term Harvest Mouse studies to be continued on the site.

Clay Lane 1 Clay Lane 2

Management - all land managers have agreed to ensure that management for Harvest

mice will be put in their site management plans. Of special importance is the cattle

grazing regime, the density of cattle and the timing. This is to avoid severely damaging

habitat, particularly during the breeding season.

A good number of volunteers are now committed to continue searching for nests and

finding new sites to continue with more trapping at other sites. SWT will make available

all the equipment required. The trapping will not be so intense and only Longworth traps

will be used.

We hosted three Harvest mouse training days for PTES covering ecology and a field visit

to check some traps and search for nests. We also included owl pellet dissection.

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Newspapers and radio stations in Surrey were very interested in the project and two

articles were published and three radio interviews held on Local Radio. BBC Radio

Surrey came out on site and did a live report on one of our early morning sessions.

We hosted three Harvest mouse training days for PTES covering ecology and going on a

field visit to check some traps and search for nests. We also included owl pellet

dissection.

Many other small mammals were caught during the trapping, two surprising catches

being a Weasel (Mustella nivales) and a Wren (Troglodytes troglodytes).

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Appendix 1

Trap sites and results

Site Grid ref Habitat HM captures Nests found Date

Thundry1 SU 89488 43944 Wet meadow 0 Yes 04.08.11

Thundry2 SU 89488 43923

Wet meadow/bog 0 Yes 04.08.11

Papercourt meadow 1 TQ 03011 56665 Wet meadow 0 Yes 23.08.11

Papercourt meadow 2 TQ 03237 56981 reedbed 0 No 23.08.11

Papercourt marshes TQ 03612 56219 reed bed 0 No 30.08.11

Royal Common 1 SU 92217 42495 Grassland 0 No 10.09.11

Royal Common 2 Su 92233 42699 Heathland 1 No 10.09.11

Manor Farm TQ 06810 59866 Reedbed 3 Yes 10.10.11

Thundry 1 SU 89169 43944 Wet Meadow 1 Yes 24.10.11

Thundry2 SU 89488 43923

Wet meadow/bog 1 Yes 31.10.11

Whitmoor Common SU 98238 53560 Heathland 2 Yes 10.9.12

Chobham Common SU 98459 64314 Grassland 0 No 18.10.12

Hedgecourt TQ 35113 40148 Reed/Grass 0 Yes 08.10.12

Ockley common SU 91454 42000 Heathland 1 Yes 18.10.12

Spynes Mere TQ 30536 52278 Reedbed 3 Yes 29.10.12

Epsom Common south TQ 18376 60987 Grassland/reeds 0 Yes 12.11.12

Epsom Common north TQ 19169 60719 Grassland/gorse 0 Yes 02.09.13

Trunley Heath SU 99821 46302 Wet meadow 0 Yes 16.09.13

Parsonage meadow SU 99451 51101 Wet meadow 0 No 30.09.13

Thundry pond/bog area

SU 89449 43991 Mixed wetland 6 Yes 14.10.13

Thundry bog SU 89455 43984 grass./bog 4 Yes 14.10.13

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Bagmore Common SU 92585 42252 Heathland 1 Yes 21.10.13

Riverside 1 TQ 00271 51589 Wetland area 23 Yes 29.10.13

Riverside 2 TQ 00317 51574 Wetland area 13 Yes 29.10.13

Riverside 1 TQ 00271 51589 Wetland area 0 Yes 07.07.14

Riverside 2 TQ 00317 51574 Wetland area 0 Yes 07.07.14

Thundry west SU 90131 43855 River edge reed 5 Yes 24.09.14

The Mill Elstead SU 90268 43897 Bramble/Balsam 9 Yes 29.09.14

Clay Lane Jacobs Well 1

TQ 00914 52549 Wet meadow 46 Yes 13.10.14

Clay Lane Jacobs Well 2

TQ 00801 52531 Bramble/Balsam 37 Yes 13.10.14

Riverside 1 TQ 00271 51589 Wetland area 27 Yes 27.10.14

Riverside 2 TQ 00317 51574 Wetland area 14 Yes 27.10.14

Thanks to People’s Trust for Endangered Species, for being the major funder for the

project and SWT for additional funding.

All the volunteer helpers without them the project would not have been possible.

Mike Waite and Jim Jones, for their technical and practical help on the project.

Photo credits, Weasel Rob Hill, Cover Harvest Mouse Graham Carey, flood Glenn

Skelton, all others D.Williams

David J. Williams

January 2015