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

 

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.

 

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