Guide by Ed Snell – Project Support & Development at NatureSpy

How many mustelid species are there in Britain?

There are seven mustelid species in Britain: weasel, stoat, American mink, polecat, pine marten, otter and badger.

Species in the mustelid family typically have a long body, short legs and thick fur. All mustelids have scent glands (with the exception of sea otters), which are used to secrete messages to one another: this may be to mark a territory or find a mate. Most mustelids are carnivorous; however, their diets can be more omnivorous based on what’s available locally and seasonally. For example, small mammals often make up a large proportion of a pine marten’s diet, but in the summertime, fruits may also be on the menu.

Mustelid identification can be tricky!

A combination of similar body shapes, elusive and mostly nocturnal behaviours can make it hard to confidently identify mustelids – that is if you’re lucky enough to see one! Camera traps are frequently used for watching and recording mustelid activity, as they operate discretely, 24/7.

In this guide, we break down the distinctive characteristics that set different mustelid species apart through illustrations and videos. We also share some top tips for camera trapping different species, some recommendations of camera traps that are excellent for the job and our go-to camera trap settings for monitoring a wide range of mustelids.

We cover all but badgers in this guide as the stripy black and white face of a badger is unmistakeable, that said… keep reading to the end for some bonus badger footage.

Weasel (Mustela nivalis)

The weasel is the smallest member of the mustelid family but relative to its body size it has a stronger bite force than a lion! This impressively powerful little mustelid is widespread in Britain. They are a territorial and solitary species, predominantly feeding on small mammals and usually nesting in abandoned dens of their prey.

Weasel identification

• Weasels are around 20cm long and have a short tail.
• They have brown fur on their backs and sides and white underparts.
• Weasels can be easily mistaken for the slightly larger stoat. A key difference between the two is in the tail. Stoats have a unique black tip on the tail, whereas a weasel has a shorter tail that’s brown all over.

How do you camera trap weasels?

Weasels live in a variety of habitats including gardens, woodlands and farmland. Due to their tiny size and speedy movement, they can be a tricky species to catch on camera. Camera traps with sensitive and fast triggers are much more likely to capture weasel footage. In woodlands, weasels sometimes follow linear features like old walls and fallen trees, so those can be good places for camera trap footage.

Stoat (Mustela erminea)

Stoats are widespread in Britain and, similarly to weasels, they are territorial, solitary and tend to nest in the dens of their prey. Rabbits are a key part of the stoat’s diet. In the colder, northern parts of their range, some stoats turn white – known as ermine – in winter, giving them better camouflage in snow.

In the southern parts of their range, stoats tend to stay brown year-round.

In cooler climates, some stoats turn white (ermine) in winter but keep the black tail tip.

Stoat identification

• Stoats are around 35-45cm from nose to tail tip.
• They are similar in appearance to weasels, but slightly larger, typically with darker brown fur on their back and creamy-coloured underparts.
• Stoats have a distinctive black tail tip. This is a key characteristic to look out for as it’s often visible even in a fleeting glimpse.

How do you camera trap stoats?

Stoats live in variety of habitats, including woodlands, grasslands, gardens and farmland. They scan their environment in a zig-zagging way, covering a lot of ground. Hedgerows and woodland edges can be good places for camera trapping stoats, as they tend to avoid being too far out in the open.

American mink (Neovison vison)

As the name suggests, American mink are a non-native species to Britain. They were brought over for use in commercial fur farms in the 1920s and were later recorded breeding in the wild in the UK in the 1950s. There is a native mink species in Europe – the European mink (Mustela lutreola) – but this species does not live in Britain.

American mink identification

• American mink are 40-70cm long with a fluffy tail. 
• They have a dark coat all over and irregular white patches of fur under the chin.
• Mink can be confused for polecats, otters and pine martens. They are a similar size to polecats, but without the polecat’s white facial fur. Pine martens have a characteristic creamy-yellow bib and otters are around twice the length of a mink, with a long, tapering tail.

How do you camera trap American mink?

American mink are semiaquatic and spend much of their lives in and near to waterways. The banks of rivers and streams are the most reliable places to see them on a camera trap as they will often skirt along the edges of waterways. Also look for natural river crossing points to aim a camera at, such as fallen trees or branches.

Polecat (Mustela putorius)

Polecats prefer lowland areas and are mainly present in Wales, the midlands and southern England, along with several other isolated pockets in Scotland and England. Historically, polecats were heavily persecuted in Britain, leading to their almost complete extermination by the early 1900s. Rodents and rabbits make up a large part of a polecat’s diet and they are less territorial than other mustelid species. They commonly den in rabbit burrows in the summer and in/near to farms in winter.

Polecat identification

• Polecats are 45-65cm long, with lighter fur markings on the face, giving a bandit mask appearance.
• They have dark brown coats with pale underfur, which is particularly visible on their sides.
• The polecat’s bandit mask is a key differentiator from other species they are potentially confused for, such as the slightly smaller American mink, which has dark fur all over, and the slightly larger pine marten, which has creamy-yellow bib fur.
• Polecats are ancestors of ferrets, and the two species can mate, creating polecat-ferret hybrids. Although polecats and polecat-ferret hybrids tend to have different fur colours, it can be challenging to tell them apart without a genetic test.

How do you camera trap polecats?

Polecats mainly live in lowland areas, yet are present in a diverse range of habitats, including woodlands, grasslands, gardens and farmland. Woodlands in valleys can be a good option for camera trapping polecats, as there’s plenty of options of trees to attach a camera to, and camera trap security is often less challenging in woodlands (just make sure you have permission from the landowner!).

Pine marten (Martes martes)

Pine martens have had a challenging history of persecution and habitat loss in Britain, but recent conservation efforts are seeing the species make a comeback. Pine martens have a varied, omnivorous diet, including small mammals, birds, insects and fruit. Much of their activity is at night-time, in and near to woodlands, where they den off the ground in elevated cavities, such hollow trees. They are a territorial species and a single pine marten’s territory can cover anywhere from 2-30km², which means they can be challenging to come by in some areas.

Pine marten identification

• Pine martens are similar in size to domestic cat.
• They have brown fur and a distinctive creamy-yellow bib on the throat and chest. The shape of the bib is unique to each animal, which means it’s possible to tell individuals apart in camera trap footage if they give the camera a good pose!
• Pine martens can be confused for polecats and mink. A key characteristic that differentiates them is the pine marten’s creamy-yellow bib. Pine martens also have a big, bushy tail in comparison to polecats and mink.

How do you camera trap pine martens?

As a territorial species that can have vast home ranges up to 30km², searching for pine martens can be a bit like trying to find a needle in a haystack. Woodlands are usually the most reliable places to catch a pine marten on camera.

Pine martens communicate with each other through their droppings (also known as scat), and inadvertently they’re communicating with people too, giving us an idea of where they are active. They will often scat on forest roads and tracks, as these are prominent locations for them to communicate with one another. Scats can be a good indicator of where to install a camera trap nearby, however the likelihood of finding scats is less common in areas where there are fewer pine martens, so if there’s no scat to be found, that doesn’t mean they’re not there!

It’s often helpful to use a camera trap on video mode when camera trapping pine martens, as this can make it much easier to see the unique shape of their creamy-yellow bibs to tell individual animals apart.

Otter (Lutra lutra)

Otters are a semi-aquatic mustelid species found in rivers, wetlands, marshlands and coastal areas throughout Britain. Poor water quality and habitat loss caused dramatic declines of otters in the UK in the 1950s and 1960s. The banning of certain pesticides, protection of the species and conservation efforts have helped otters make a comeback over the past 60 years. Otters mainly feed on fish and they den near to water in cavities called holts.

Otter identification

• Otters are a larger mustelid species at 90-135cm long from nose to tail tip.
• They have brown fur with paler underparts, a long, tapering tail and small ears.
• They are sometimes confused with American mink, since both otters and mink tend to stick close to water. Otters are much larger than mink (up to 135cm compared to mink up to 70cm), have paler fur, and a long tail that tapers to more of a point, compared to the mink’s blunter tail tip.

How do you camera trap otters?

River and stream banks are a good places to observe otters with camera traps. Camera security can be an issue in some situations, so it’s often better to attach the camera to a tree on a bank using a cable lock where possible.

There are a couple of unique challenges with camera trapping otters:

• Otters are very well insulated by their thick fur, which means they can appear the same temperature as their surroundings. Since camera traps rely on movement and changes in ambient heat to trigger, this can result in cameras triggering later than anticipated. This can be countered to some extent by using a camera with a sensitive trigger.
• Otters often appear to notice camera traps and, in some instances, will move away. This may be because they can see the infrared LEDs of low-glow cameras, so no-glow LED cameras could be a more discrete option (learn more about camera trap LEDs here).

Camera trap setup

Choosing a trail camera for mustelid monitoring

There are several key features of trail camera to consider for mustelid monitoring.

Photo vs. video. For simply detecting presence of a species, photo mode works well. To observe behaviours, video is best.

Clear night-time images. All British mustelid species are largely nocturnal in their activity, so having sharp night-time footage is important for accurate identification and observing behaviours.

A camera with a fast, sensitive trigger is especially important for recording weasels and otters:

• Weasels are so small that a sensitive trigger is essential to detect an animal at all, and they’re such a fast-moving species it’s vital that the camera responds fast.
• Due to their thick fur and low body temperature when emerging from water, otters can appear very similar in temperature to their surroundings, this means that cameras without a sensitive trigger can fail to detect a change in ambient heat, so a sensitive trigger is key for otter monitoring.

Recommended trail cameras

Below we list some of our favourite camera trap models for mustelid monitoring based on our fieldwork experience through projects such as the Yorkshire Pine Marten Project and Alladale Wilderness Reserve’s mammal monitoring.

The ultimate trail cameras for mustelid monitoring

Browning Recon Force Elite HP5 (all but otters) & Spec Ops Elite HP5 (all UK mustelids).

• Excellent video & photo quality, night and day.
• Lightning-fast trigger speeds for capturing quick activity.
• Sensitive trigger performs well with smaller species like weasels and detecting the colder appearance of well-insulated otters.
• Efficient with batteries, performing best with Energizer Ultimate Lithium AA and performing well with Panasonic Eneloop Pro rechargeable batteries.
• No-glow infrared LEDs of the Spec Ops Elite are more discrete for monitoring species such as otters that may detect low-glow infrared LEDs.

Browning Recon Force Elite HP5 trail camera

Other great camera traps for mustelid monitoring

NatureSpy Ursus trail camera.

• A feature-packed, budget-friendly trail camera.
• Good quality video and photo, night and day.
• Fast and sensitive trigger.
• No-glow infrared LED, great for monitoring all mustelid species.

NatureSpy Ursus trail camera

Good all-round camera trap settings

The camera trap settings listed below are a good starting place for mustelid monitoring. We recommend tweaking them to suit different monitoring needs.

• Footage type – Photo for species identification only or video to identify species and see behaviours.
• Video length – 20 seconds is adequate in most scenarios, capturing plenty of activity and reducing the amount of empty footage.
• Video quality – Highest.
• Photo delay – 1 second if leaving the camera for a shorter duration (e.g. 2 weeks), consider longer delays if leaving the camera for more than 1 month to help manage quantity of footage.
• Trigger sensitivity / motion detection – High sensitivity / long range, to help with reliable camera activation.
• Trigger speed – Fastest option, to help capture quick activity.
• Infrared LED flash power – Long range / High, for best night-time illumination.