The NHBS Guide to Small Mammal Trapping

Field vole (Microtus agrestis)

Small mammals form a vital component of our terrestrial ecosystems, both by contributing to overall biodiversity and providing prey for carnivores such as owls, pine martens and weasels. Survey data for many of our small mammal species is insufficient for them to be assessed as part of the UK BAP process and so supporting our national monitoring programme is incredibly important.

One of the most common ways of monitoring small mammals is through the use of live traps. These allow a range of species to be monitored simultaneously, and also allow biometric data such as weight and sex to be collected. In addition, estimates of population size and structure can be calculated using capture-mark-recapture (CMR) techniques. The use of live traps is also a great way for getting volunteers involved and providing them with an up-close experience of the animals they are passionate about.

Live-catch techniques, however, do have a few disadvantages in that populations can be affected by disturbance or mortality. Live-trapping is also unsuitable in certain areas (such as urban or busy rural regions) and requires a relatively large amount of time and expenditure.

Here we will take a look at some of the most commonly available live-traps used for small mammal survey.

Longworth Trap

Longworth Small Mammal Trap

The Longworth trap is made from aluminium which makes it lightweight for field use. This trap has been widely used in the UK for many years.

The trap consists of two parts: a tunnel which contains the door tripping mechanism, and a nest box, which is attached to the back of the tunnel. The nest box provides a large space for food and bedding material to ensure that the trapped animal is comfortable until release.

Advantages
• Widely used for many years; well documented in scientific literature
• Lightweight and durable
• Sensitivity of the trip mechanism can be adjusted
• Door can be locked open for pre-baiting

Disadvantages:
• Expensive
• Replacement parts not available
• Larger species can occasionally trip the trap without being caught
• Pygmy shrews may be too light to trigger the trap mechanism

Sherman Trap

Sherman Trap

Sherman traps work by use of a triggered platform which causes the door to shut when the animal enters. It folds down to a size and shape which is easy to transport.

Sherman traps are available in a range of different sizes to suit the species that you are hoping to catch. They can be purchased in aluminium or as a galvanised version which is more resistant to rusting.

Advantages:
• Lightweight and foldable – easy to transport and store
• Different sizes available, including long versions
• Easy to clean

Disadvantages:
• Difficult to add bedding/food as this interferes with the trap mechanism
• Traps may distort over time with repeated folding
• Danger of long tails being trapped in the door

BioEcoSS TubeTrap

The TubeTrap is a relatively new addition to the mammal trapping range and features an innovative design. It provides a safe method of trapping even the smallest mammals such as shrews.

The robust plastic construction has self-lubricating and fully replaceable parts. It can be purchased either with or without a shrew hole in the door. Spare doors are also available which means that you can convert the trap between shrew and non-shrew versions quickly and easily.

Advantages:
• All parts are easily user-replaceable
• Door can be locked open for pre-baiting
• Trigger sensitivity is easily adjustable; suitable for pygmy shrews
• Green colour of trap makes it inconspicuous in the field

Disadvantages:
• Door is a little fiddly to set – particularly for larger fingers
• Relatively new design means it has been tested fewer times in the field in comparison to Longworth or Sherman Traps

Economy Mammal Trip-Trap

Economy Mammal Trip-Trap

The Economy Trip-Trap provides a cheaper alternative to other mammal traps.  It has a traditional treadle design which closes the door behind the animal when it enters the trap.

This lightweight trap is suitable for short-term or occasional use and is also popular for trapping mice indoors either for surveying or for relocation.

Advantages:
• Cheap and lightweight
• Transparent for easy inspection
• Good for indoor use

Disadvantages:
• Doesn’t work well in wet/humid conditions
• Can’t pre-bait or change trigger sensitivity
• Trapped animals may chew through the trap

Pitfall Traps

P2.5 litre Plastic Bucketitfall Traps consist of a container which is sunk into the ground, into which small mammals can be caught. Traps can be baited if required and drift fencing can also be used to direct animals into the trap.

Small cans or buckets make ideal pitfall traps. If using buckets, lids can be fitted when not in use, which means that traps can remain in situ for extended periods of time.

Advantages:
• Able to catch multiple individuals
• Low maintenance

Disadvantages:
• More labour intensive than box traps to set up
• Trapped animals may attack eachother or be eaten by predators
• May become waterlogged in damp areas or in bad weather

Other survey methods

Other methods of surveying for small mammals include the analysis of owl pellets for mammal remains and the use of dormouse nest tubes. Hair and footprint tubes are also useful as well as searching for field signs such as tracks and faeces.

A comprehensive monitoring programme will most likely involve a combination of these methods, depending on the availability of participants and volunteers and the type of habitat present locally.

If you are interested in becoming involved in mammal survey in the UK, take a look at the Mammal Society website where you will find information on local recording groups, training opportunities and the latest mammal-related research.

Our full range of mammal traps can be found on our website.

 

Interview with Simon Poulton about the new BioEcoSS TubeTrap

Simon Poulton struggling to enter data in the field
Simon Poulton struggling to enter data in the field

The BioEcoSS TubeTrap is a new product for ecologists and researchers conducting mammal surveys. The innovative design is the work of data consultant Simon Poulton, who told us more about his company and his revolutionary new small mammal trap.

Tell us a little about your organisation and how you got started.
BioEcoSS Ltd is a consultancy specialising in all aspects of ecological data handling and analysis. I became a consultant after taking voluntary severance from ADAS, which was the scientific and advisory arm of the old MAFF – precursor to DEFRA, for the youngsters among you. I had worked for them for 14 years, developing from basic wildlife advice through to coordinating the national monitoring of Environmentally Sensitive Areas and other agri-environment schemes. Change was in the air, with ADAS becoming a “Next-Steps Agency”. So, I decided to go it alone, allowing me to concentrate more on the practical side of database design and statistical analysis – rather than managing teams and editing their reports. It also allowed me to select my clients to focus more on the taxa that I was interested in – primarily mammals and birds.

Why the name? Well, when I set up as a consultant I had a very loyal spaniel call Bess. Struggling to come up with a descriptive name that had “ecology” and “statistics” in it, a mischievous friend took one look at the adoring dog at my feet, and suggested BESS. So, I became Biological & Ecological Statistical Services! Bit of a stretch – but it caught on. Then when I converted to a limited company five years later, I thought I’d better have something a bit more respectable – so BioEcoSS Ltd was born.
Over the last 18 years, I’ve had a good number of clients, including universities, NGOs such as the Mammal Society, Vincent Wildlife Trust & BTO and government departments such as Natural England, CCW and JNCC. My work has generally fallen into two types:

a) ecological database design, and
b) statistical analysis of existing datasets.

However, in all my projects, I’ve tried to emphasise the importance of incorporating these aspects at the project planning stage – very often they’re not! So, it’s not unusual for clients to turn up with a dataset that’s been stored in a spreadsheet, riven with errors, and with a survey design that just doesn’t give them the power they need to detect change or spatial variation. I do what I can, but it would be so much better if these aspects were considered more carefully at the outset as part of an integrated design – sorry, that’s a bit of a lecture!

What was the original inspiration behind the TubeTrap?

BioEcoSS TubeTrap
BioEcoSS TubeTrap

About six or seven years ago, when I was on the council of the Mammal Society, we were discussing the setting up of a national small mammal monitoring scheme. The then chair, Dr Johnny Birks (very well-known to all mammalogists), lent back in his chair and sighed “It’s such a shame we don’t have a good trap at a reasonable price!”. We all agreed that we would have to focus on non-invasive methods for a large-scale, mass-participation survey – which is not a bad thing anyway – but there was still a need for trapping to provide high quality data.

On the train home I started thinking about this idea. Database design is a very creative and practical process –understanding the requirements of the user and combining these with practical and intuitive solutions. And I felt I was fairly practical – good with wood and I seem to be forever re-plumbing my house! As the son of an engineer, I thought I might be able to come up with a good design for a mouse trap. After all, I had been using the trusty Longworth and even some old Shermans for over 25 years, so I knew their faults and limitations.

So over the next 18 months I set out to build a prototype. I was certain that injection moulding was the answer to producing large numbers of cheap traps and I was very lucky to get some financial help from the, now sadly defunct, Manufacturing Advisory Service. I also fell on my feet by finding two incredibly helpful and innovative small companies in the West Midlands; an injection tool-making company (BFT Engineering) and an injection moulding company (BTF Polymers). (The names are purely coincidental – they’re not related in any way – but they continue to cause me total confusion!) These guys were enormously helpful in designing the tools and producing prototypes for testing. So – TubeTraps are entirely British made!

How does the TubeTrap compare to other small mammal traps on the market?
Well! What do you expect me to say – pretty good I reckon! Seriously –I think there are three primary aspects to the efficacy of a small mammal trap:

1) How well do they catch?
2) How humane are they?
3) How practical are they to use?

In the UK the main competitor is, obviously, the Longworth. This has remained virtually unchanged over the last 50 years so, in an evolutionary sense, it must be pretty well adapted to what it does. I’ve carried out some comparative trials (as have six or seven users) which shows that TubeTraps catch just as well as Longworths. As the number of trials increases, there’s even some evidence that they are better at catching very small animals such as pygmy shrews and harvest mice. I’m hoping that two students from UEA will be trialling the traps this autumn to provide enough data to show this is statistically significant. I’ve not compared them directly with Shermans or Trip Traps, but people have told me, anecdotally, that TubeTraps have a higher capture-rate.

Episoriculus leucops
Episoriculus leucops

Part of the design was to make a trap that was as humane as possible. Obviously, the correct setting and use of traps goes a long way to ensure the survival of captured animals – in particular, live invertebrate food for shrews is essential, as is regular checking. But I wanted the TubeTrap to help prevent exposure of animals, so the use of plastic and the double-walled nest-box provide much better insulation. I’ve also had a bit of a theory about shrew deaths. A very light animal (say a pygmy or juvenile common shrew) enters a trap without tripping it, scoffs all the food and then leaves. Along comes an adult shrew, trips the door and finds a trap with no food. Result – starvation. So I think the very sensitive and stable mechanism of TubeTraps will help prevent this situation.

The practicality aspects of the design were very important, especially setting the trap and cleaning. The nestbox and tunnel parts of the trap snap together very intuitively and are virtually impossible to pop open accidentally – unlike a poorly set Longworth. The smooth, cylindrical profile of the trap makes it very easy to push into dense vegetation and remove for emptying. Again – in the past, I’ve popped open Longworths when pulling them out of hedgerows as the corners of the nest box or the hook of the pin hinge catches on a bramble. The TubeTrap’s white doors are very easy to see, even in poor light, so it’s much easier to check when they are closed. So too with the pre-bait lock – it has a very visual appearance, so it’s much more difficult to leave a trap locked open by mistake. The round profile of the nestbox and the flat base of the tunnel with no side-walls make them very easy to clean. Finally – and possibly most importantly, all parts of the trap snap together, so it’s very easy to replace any damaged parts. I always carry a few spare triggers (which can get chewed) and the elastic springs for replacement in the field.

Development of the TubeTrap is continuous and I’m pleased to say that NHBS is stocking the new Mark II version. This has a more stable trip mechanism, which is counter-balanced, making it much more difficult to accidentally trip when knocked or jolted. This also makes it easier to set TubeTraps in awkward places or above-ground attached to branches or poles. There was an issue in the original design with surface-tension from rainwater holding the doors open, but a number of modifications in the new Mark II trap have addressed this.

How and where have TubeTraps been used and what is the most interesting species you have caught?

TubeTraps have been used by a number of universities, county mammal groups and wildlife trusts. As far as I know, they are being used for mammal research, survey and monitoring. Also, I know that the trusts have used them for training and open-days, so they’re proving versatile.
As you may have gathered from some of the time periods I mentioned earlier, I’m getting a bit long-in-the-tooth! But, a few years ago I finally started the PhD (at UEA) that I’d never got around to doing. I’m looking at altitudinal variation in small mammal communities in the central Himalayas of Nepal – using 120 of my traps of course! I’ve done three seasons’ fieldwork and caught 795 animals at altitudes from 1300m to 4200m. The traps have performed very well and have been catching hundreds of tiny shrews, as well as some pretty hefty rats weighing over 100g. The CarryCases have also been fantastic, not just for carrying the traps, but as dissection and dinner tables! There’s no doubt in my mind that the best animal I have caught is a tiny shrew called Episoriculus leucops – only 5g in weight, but with the longest tail you’ve ever seen (pic above).

BioEcoSS TubeTrap Carry Case
BioEcoSS TubeTrap Carry Case

What do you consider the most important achievement of your organisation in recent years?
That’s a tricky question! I think just because of the size of the project and its subject – the Environmental Monitoring Database for Natural England. I’ve worked on this for over ten years, bringing together into a single database all the agri-environment monitoring data carried out since 1987. There are over 4.25 million data items in this database, which makes it a unique resource. But how can I not mention the work I’ve done with excellent conservation organisations such as the Mammal Society (scoping and setting up the national small mammal monitoring scheme with Phoebe Carter and Johnny Birks) or the Vincent Wildlife Trust (analysing their fantastic dataset on batbox usage collected by the tireless Colin Morris and his colleagues).

But, I also hope I’ve made a real contribution in Nepal, mostly by giving young ecologists hands-on experience of fieldwork, statistical advice and training that they wouldn’t otherwise have access to. I should say that this has been a two-way process and I’ve had fantastic support from them (Hari Basnet, Sagar Dahal, Hem Kathuwal and others). I would also like to mention my friends and colleagues, Laxman Poudyal, Sujan Maharjan, Hem Sagar Baral, Sharad Singh and Dibesh Karmacharya – who have all helped in this reciprocal process. And – most importantly – the porters, whose superhuman efforts at carrying traps, collecting water and wood, cooking amazing food and generally remaining completely cheerful made this work possible.

Simon, Suman, Padam, Hari and Sujan with Machhupuchhare behind.
Simon, Suman, Padam, Hari and Sujan with Machhupuchhare behind

What is your most memorable wildlife encounter?
Another tricky one! I’ve had a long-lasting love affair with India and Nepal, so I should say the tigers I saw in Kanha and Ranthambore National Parks, or Indian one-horned rhinos in Kazirangha or the fantastic nilgai in Sariska. But, actually, the most thrilling was probably five years ago at 3500m in Nepal when my colleagues and I came across a very (I mean VERY) fresh set of prints of himalayan black bear only a few meters from our camp-site. That certainly caused a stir amongst the porters! Then again – the most sublime moment was probably during that expedition, being out just before dawn, when the koklass pheasants started calling. Their harsh cries carry for hundreds of metres through the gloom – the Nepalis’ literal interpretation is “How are you, Uncle?”. It’s a spine-tingling memory just thinking about it.

Any new inventions in the pipeline?
I might have! Actually, a client from Ireland recently asked if I could produce traps with shrew holes. It had been on my mind for a while, so I made 30 doors with shrew holes for her. She’s trialling them now and if they work well, I’ll make them generally available. The benefit of putting the holes in the doors is that you can easily snap these out and replace them with standard doors if you don’t want the shrew holes.

I do have another idea, but I’m keeping my cards close to my chest at the moment. Suffice it to say – if it works it could revolutionise small mammal trapping – I’m saying no more!

Find out more about the BioEcoSS TubeTrap at NHBS

Celebrating 60 years and Counting of the Longworth Mammal Trap

The Longworth mammal trap was invented in 1949 and is celebrating over 60 years of service. As the most widely used and respected small mammal trap in use in Europe, it is familiar to many of us. But how well do you actually know it? Read on for some facts on the Longworth trap you may or may not know!

The Longworth mammal trap was invented in 1949 and is celebrating over 60 years of service.  As the most widely used and respected small mammal trap in use in Europe, it is familiar to many of us.  But how well do you actually know it?  Read on for some facts on the Longworth trap you may or may not know!

Why is it called the Longworth trap?

Longworth TrapUnfortunately it’s not because Mr Longworth invented it.  The Longworth trap was invented by Chitty & Kempson (1949).   At the time they were working at the Department for Zoological Field Studies at the University of Oxford.  They arranged commercial production through another Oxford-based organisation, the Longworth Scientific Instrument Co. Ltd, and the trap took the same name.  The Longworth Scientific Instrument Co. was founded in 1943 by another group of Oxford academics.  Personnel from the Department of Anaesthetics formed the company to manufacture technical medical equipment such as the Macintosh Laryngoscope.  As the Longworth trap required similar manufacturing processes, it made sense for the Longworth Co. to manufacture Chitty & Kempson’s trap.  Due to its strong geographical links, you may also have heard the Longworth trap called the Oxford trap, although a prerequisite for this is a long memory, even longer beard and elbow patches!

Are Longworth traps good for sampling shrews?

Longworth trap with shrew holeTraditionally there has been a belief that pitfalls rather than small mammal traps such as the Longworth should be used for catching small shrews (e.g. Williams & Braun, 1983).  However, recent evidence may suggest that this is not always the case (e.g. Anthony et al., 2005).  Every trap design will introduce some type of bias, so the key is to ensure as fair a test as possible.  Comparing two datasets obtained using different trap designs will obviously introduce error.  If you are particularly concerned about small shrews then consider using Longworth traps in tandem with pitfall traps (using drift fences with the pitfalls will generally increase success).  Remember that vegetation type and even trap age may possibly influence trap success.  The fact that Longworth traps are incredibly durable with many still in use after 30 years of service makes them ideal for repeat long term surveys.  And remember, you won’t catch any small shrews with the Longworth trap with optional shrew escape hole!

How do I bait the trap?

The bait smell will initially attract the mammal to the trap so try to handle the bait as little as possible, especially if you’ve got smLongworth trapelly (perfumed or otherwise!) hands.  Shrews and other insectivorous mammals will need invertebrates; try blowfly pupae available from fishing tackle shops.  Otherwise seeds, raisins, barley, oats or even chocolate will do.  By using fruit or vegetables (apples and carrot can work well), you can also provide an essential source of water for the trapped mammal.  The type of bait used is probably of little importance in trap success (Sealander & James, 1958), and by using the same bait in all traps the effect of bait type will be nullified.

Acclimatising mammals to the trap is particularly important, especially when sampling more timid species.  The Longworth is ideal for this as it can be set not to trigger when an animal enters.  Bait the trap in the ‘non-trigger’ setting and leave for several days for this acclimatisation to occur.  But remember, by doing this you may attract other individuals from surrounding areas and inflate population density estimates.

Also remember to provide some bedding in the trap; hay or shredded paper work best.  If using leaves (or indeed anything else), make sure they are dry as damp nest material can chill the animal.  Change the bedding after every capture to ensure a dry clean trap for the next unlucky victim.

Where should I place the trap?

Place the trap in a sheltered secluded location, ideally in thick vegetation, but make sure you can find it again.  A bright marker on the trap can aid location of it but can also make it more conspicuous to the public.  Place the leading edge of the trap flush with the ground to encourage animals to enter.  Ensure the nesting box is at a slight angle to encourage urine to drain away.  When placing the trap, look out for signs of mammal activity (droppings, runs through vegetation, chewed food, etc).  These are unlikely to be in the middle of clearings as small mammals tend to prefer margins, hedges, etc.  Usually multiple traps will be deployed.  By deploying in a grid formation you will get a better idea of population density, whilst straight line deployment is useful for covering a cross section of habitats or following linear features (hedgerows, boundaries, etc).

Is there a cheaper alternative?

Mammal Trip-TrapLongworth traps are expensive and the initial cost of buying the traps can be high.  However, it is worth remembering than Longworth traps will last decades if looked after properly so the cost of the trap over its lifetime is actually quite cheap.  Nevertheless, a cheap alternative is the Mammal Trip-Trap.  This is a simpler trap to the Longworth and designed for occasional use.  It is made from robust plastic rather than the Longworth’s aluminium, but also features a trapping tunnel and nest box.  However, as woodmice have on occasion been known to chew through the aluminium on a Longworth trap, the plastic trip-trap may be severely damaged unless checked very frequently.

Longworth trapWhichever trap you use, remember to check them at least every 12 hours (and even less for shrews as they are particularly prone to mortality in traps).  You also need a licence to trap shrews.  If you have any other queries on the Longworth trap or Trip-Trap then please get in touch.

References

Anthony NM et al. (2005) Comparative effectiveness of Longworth and Sherman live traps. Wildlife Society Bulletin 33: 1018-1026
Chitty D & Kempson (1949) Prebaiting small mammals and a new design of live trap. Ecology 30: 536-542
Sealander JA & James D (1958) Relative efficiency of different small mammal traps. Journal of Mammalogy 39: 215-223
Whittaker JC & Feldhammer (2000) Effectiveness of three types of live trap for Blarina (Insectivora: Soricidiae) and description of new trap design. Mammalia 64: 118-124
Williams DF & Braun SE (1983) Comparison of pitfall and conventional traps for sampling small mammal populations. Journal of Wildlife Management 47: 841-845