Defending the Tay: Scaling up Mink Trapping for Conservation

Cat Cooper, Project Officer, Scottish Invasive Species Initiative, published March 2025

When the Scottish Invasive Species Initiative began operations in 2018 we faced a situation where there was no carryover mink trapping network remaining from the Scottish Mink Initiative (SMI) which ended in 2015. This meant that we had to rebuild a trapping network from scratch and in combination with rolling out landscape scale plant control in the Tay system – mink are not our sole focus and so our resources are spread more widely. Our initial emphasis was placed on re-establishing a core trapping network on the main stem of the Tay and Tummel, with targeted deployment where possible to smaller rivers and tributaries and areas of environmental importance like the Tay Reedbeds and Loch of the Lowes. From 2018 to 2024 a robust network was built up and maintained in these areas, catching more mink than any other Scottish Invasive Species Initiative project area in that time. However, with additional seasonal project staff employed in 2024, there was an opportunity to grow the network to fill gaps and expand west, to bring rivers like the Earn into the project area. Cat Cooper (now Project Officer for the Esk catchments) played a leading role in delivering that expansion over her time working with us as a Seasonal Project Officer in 2024.

“Remoti – Unit Activation.”

These words via text have become a regular occurrence in the past couple of months, and with each comes the excitement of knowing that there may be another American mink waiting in a live trap within the Tay system…

I began my seasonal role in May 2024 with the Scottish Invasive Species Initiative, working alongside the Project Officer on the River Tay and its tributaries. As part of my role I was given the opportunity to work on the expansion of the mink trapping network into the River Earn and to fill in a gap within the current network on the River Ericht. American mink trapping was a new undertaking for me and I was keen to get started.

The Earn: Expanding the network

The Earn is roughly 74km long, beginning at Loch Earn on the edge of the Trossachs and joining the Tay at Abernethy. Whilst we knew there was a population of American mink on the Earn, this tributary in the south-west of the Tay catchment (a border region for the project) hadn’t yet been reached. However, contact had been made with the River Earn Improvement Association to establish interest, and a list of willing volunteers was waiting to get set up and change that situation.

Remoti units are attached to a live capture trap and triggered when the trap closes – this sends a text message as an alert

A raft deployed on a tributary of the Earn. This was a rockier area which meant we had to use the trees for anchors.

Once I had my list, I reached out to each potential volunteer and arranged a site visit to determine a suitable location for a raft and live trap. Many of our new recruits are gamekeepers, ghillies and estate employees who have been working the land for years (in some cases over 40!!) and their knowledge of the area and past mink experiences was invaluable to identify the right locations.

At each site we looked for areas where mink had been spotted historically but also for locations that would provide excellent territory for them. Ponds, streams and ditches were all investigated as well as the main stem of rivers and their confluences (where two or more watercourses join).

Once we had agreed on a site the next phase would begin – deploying the equipment as quickly as possible. Our set up includes a floating raft and tunnel, a live capture trap, and a Remoti unit. The Remoti devices have proven to be invaluable to many of our new volunteers – particularly if they are busy with their day-to-day tasks or responsible for large areas of land or river beats. The Remoti unit is attached to a live capture trap and is triggered when the trap closes – this sends a text message to both the volunteer and the Project Officer to alert them. On our first new site success arrived much faster than even we had expected, with five mink caught and dispatched within the first week of operation. Many of these captures were on an estate pond but we also had success on the main stem of the river… we even had two mink in one day!

Our volunteer decided to paint his trap to conceal it and then moved it from the original location to a field ditch closer to the Earn. This was successful and a mink was captured here.

Our first raft on the Earn system was deployed on a duck pond which proved to be a huge success.

Sometimes we didn’t get the trap position quite right first time around and needed to make small changes to the location to maximise the chances of mink entering the trap – and minimise the likelihood of non-target species being captured. One volunteer had two red squirrels and even a hedgehog but these were safely released to continue their day and we subsequently moved the raft…and even camouflaged it!

By the end of 2024 we had 18 mink captures on the River Earn and 10 volunteers in place, with twelve traps deployed and a further ten awaiting placement next season, with coverage from Bridge of Earn all the way to Loch Earn. Mink activity slows down over winter and most volunteers will bring their equipment out of the water to avoid damage and lost equipment in storms and spates, but this end of year coverage puts us in an excellent position to hit the ground running in spring 2025.

The Ericht: A Gap in the Network

The Ericht originates in Highland Perthshire, where the Rivers Ardle and Blackwater meet near the Spittal of Glenshee, and flows down to Blairgowrie where it merges with the Isla. Historically the Ericht was a vital source of power, driving numerous mills and factories along its banks, particularly in Blairgowrie. Today the river is known for its salmon fishing, diverse habitats, and scenic walks. However, like many Scottish waterways, it faces ecological threats from invasive species like the American mink.

The Ericht has proved tricky for us to set up a consistent network so this was a key target area for me in May 2024. The only coverage up until this point had been through a gamekeeper who began trapping on the upper Ericht in mid-2023.

As with the River Earn, we had already received interest from one of the local estates. The keepers, ghillies, and their guests were regularly seeing mink travelling up the river systems so they were keen to lend their time and expertise to the project. One volunteer, Adam, had several sites in mind, including an adventurously out of the way hill loch where he had spotted mink in the past, and a confluence on the main river. One obstacle we faced here was the patchy mobile network. Remoti units operate using mobile phone masts and in Highland Perthshire this can be tricky, but Adam was happy to trial these and give it a go – knowing that he might have some additional journeys to make if the signal were to dip out.

Adam with our rather adventurous loch raft. Sadly signal wasn’t reliable enough, so the raft was moved to a different spot.

An adult female mink, captured by Adam on the Ericht

Rafts were placed and traps were set. On this occasion we decided to maximise our chances by placing mink scent in the back of the traps and less than 24 hours later we had a juvenile female – followed the next day by a young male!

In total, the Ericht had 16 mink captures in 2024 and, like the Earn, we expect to catch more when activity heightens again in spring. We now have six volunteers together monitoring 11 traps in the Ericht catchment – thank you to everyone who has signed up!

The Earn and Ericht expansion have already seen 34 mink captures between them since we started to expand these networks in July 2024. We are also delighted to welcome Comrie Men’s Shed to the project, our newest construction recruits who have kindly agreed to make rafts and tunnels for us to be deployed in the new year. Volunteers are absolutely essential to the Scottish Invasive Species Initiative and without them there simply wouldn’t be the time and skills available to cover such an expansive area. Thank you to each and every person who has offered advice, cups of coffee and, most importantly, their time to get these new networks up and running.

In total the Scottish Invasive Species Initiative captured 74 American mink from across the Tay catchment in 2024, with the help of over 50 volunteers. Of these, 34 captures were from the Earn and Ericht systems – a great success following these local expansion efforts. American mink are an invasive non-native species which have severe detrimental impacts on native wildlife. By controlling their population we aim to reduce their impact on native species and protect local wildlife. Thank you to everyone who has been involved across the Tay catchment!

To find out more about the Scottish Invasive Species Initiative and how to get involved, you can visit our website, follow us on social media or contact us on sisi@nature.scot

Native vs Invasive: When Small Differences Make a Big Impact

Connor Wood, Seasonal Project Officer and PhD Student with the University of the West of Scotland, January 2025

Introduction

We know that invasive non-native species are a major threat to biodiversity, but the danger they pose to our ecosystems can often be hard to see. Picture a sewer pumping sludge into a river or a forest being cleared and replaced with concrete—those are obvious, visible threats. But when an ecosystem is taken over by a non-native species, the damage can be much harder to recognize. Unless you can identify which species are native and which are non-native and invasive, the problem might not stand out. An understanding of why these invaders are a threat requires knowledge of their subtle differences from similar native species and how these differences can disrupt the balance of the ecosystem.

At first glance, some invasive non-native species don’t seem all that different from their closely related native counterparts. Take the invasive giant hogweed (Heracleum mantegazzianum) and the native common hogweed (Heracleum sphondylium) — sure, the invader stands much taller than its British relative, but they appear to function quite similarly overall. Or consider the Eurasian otter (Lutra lutra) and American mink (Neovison vison): the otter may be noticeably larger, but both are semi-aquatic predators from the weasel family, swimming through the same rivers. So, why is one a valued part of our ecosystem and the other a serious biodiversity threat?

*Connor (left) took a break from his PhD research this summer to join us in the Spey catchment and help tackle invasive non-native species like American mink and giant hogweed*

*Connor sets up a mink trap on a floating raft*

The answer isn’t just blind favouritism for native species. The danger posed by invasive species is very real, and it often comes down to small, crucial details – differences in biological traits (for example, size or fecundity) and how these traits shape their interactions with other species.

This is the focus of my ongoing PhD research, where I compare the traits of a native freshwater shrimp (Gammarus pulex) with two closely related invasive species (the killer- and demon shrimp, Dikerogammarus species) to understand how these differences play out. In this blog, I’ll focus on the traits that give invasive species like giant hogweed and American mink their destructive edge over native species.

Case Study 1: Giant Hogweed vs Common Hogweed

Giant hogweed, a member of the carrot family from the Caucasus Mountains, is closely related to common hogweed which is native to the UK. In fact, they’re so closely related they’re even capable of producing the occasional hybrid offspring [14]. Despite these similarities, their ecological roles differ dramatically. Here are some of the key differences between them which can explain why giant hogweed is considered a high-impact invader.

*Common hogweed (above) is a native species which is very similar to the invasive giant hogweed (right). Photo credit:* *Rasbak, Wikimedia Commons.*

*There are key biological differences which make giant hogweed (above) a high impact invader.*

Growth and Light Competition
Giant hogweed can grow up to 5 meters tall, dwarfing the smaller common hogweed which grows to a maximum of only 2 metres. The leaves of giant hogweed are similarly oversized, spanning 1.5 to 3 metres in width compared to the much smaller 55cm length leaves of the common hogweed. This size, when combined with rapid vegetative growth, allows giant hogweed to form dense leaf canopies that block out sunlight for smaller native plants. Competition for light is one of the major drivers of plant community composition [21], and the giant hogweed has a clear advantage in this contest.

Seed production and Emergence
High reproductive output is one of the most commonly reoccurring traits in successful and high impact invasive species [17]. Looking at the hogweed species, we can see a major difference between the two. Both species take around three years to reach the flowering stage. However, the reproductive potential of giant hogweed far outstrips its native counterpart. While common hogweed produces about 850 seeds per flowering season and usually flowers two to three times during its lifespan [16], giant hogweed can produce anywhere from 20,000 to a staggering 100,000 seeds in a single season. These seeds also germinate more frequently and emerge earlier in the season, giving the giant hogweed a big head start on outgrowing the competition [15]. What’s more, the seeds can remain viable in the soil for up to 15 years.

The reason for this difference lies in the giant hogweeds evolutionary history – the high seed production is a vital adaptation to survive the extreme cold and nutrient poor soil of the mountains in its native range. This reproductive advantage means that once giant hogweed takes hold, it is difficult to eradicate, allowing it to spread rapidly and persistently.

*The oversized leaves of giant hogweed form dense canopies which block out light while it’s high reproductive output allows it to spread *rapidly* in new environments*

*Brown seedheads from the previous summer are visible among a dense covering of giant hogweed leaves*

Toxic sap
Giant hogweed is notorious for its highly toxic sap, which can cause painful, long-lasting burns due to a chemical compound called furocoumarin. While common hogweed also contains furocoumarin and can cause skin irritation, its effects are far milder because the chemical is present in significantly lower quantities. Whether giant hogweed’s toxic sap provides an ecological advantage over common hogweed or other native plants remains unclear—it may deter some herbivores [20], but our sheep trials have shown that certain livestock are unaffected. However, the difference in impact on human health is undeniable, with giant hogweed posing a far greater threat.

Insects and Pollination
Common hogweed is a vital part of the local insect food web, attracting a broad variety of pollinators such as bumblebees, butterflies, hoverflies, and beetles. These pollinators play an important role in maintaining biodiversity. Giant hogweed, on the other hand, attracts a much narrower range of insects. Studies have shown that areas dominated by giant hogweed experience a decrease in pollinator diversity [13], which can have ripple effects throughout the entire ecosystem. The loss of specialist insect species in areas overtaken by giant hogweed is particularly concerning, as it impacts the broader insect community and the health of native plants that rely on these pollinators [19].

*Common hogweed attracts a variety of native pollinators, providing a food source for bees, butterflies, hoverflies and beetles. Photo credit:* *Anne Burgess, Wikimedia Commons.*

Summary
Giant hogweed’s size, reproductive capacity and highly toxic defence strategies have made it a highly successful and destructive invader. As they overtake and dominate plant communities, the abundance and diversity of both native plant species and specialist insect species declines in turn. Without this native biodiversity and the ecosystem services it provides – pollination, nutrient cycling and habitat creation – the ecosystem suffers as a whole.

Case Study 2: American Mink vs. Native Otter

Background
The American mink and the European otter are both top predators, members of the weasel family and share similar wetland and river habitats across the UK. Despite these overlaps, these two species have sharply different ecological impacts. The American mink poses a significant threat to native species, particularly causing dramatic declines in water vole and ground-nesting bird populations [1], whereas the otter is often regarded a keystone species crucial in maintaining ecosystem health. These are some of the trait differences that make mink a danger when compared to the otter.

*The European otter (above) and American mink (right) are both semi-aquatic mustelids which inhabit rivers, wetlands and coastlines in Scotland. Photo credit:* *Peter Trimming, Wikimedia Commons*

*Despite their similarities, the invasive American mink (above) has a very different ecological impact compared to the native European otter (left). Photo credit: NatureScot*

Size Differences and Competitive Advantage
One key difference between the two species is size. Quite the opposite from the giant- and common hogweed, in this case the native otter is the larger animal. Otters can grow up to 130 cm in length, while mink are much smaller, ranging from 42 to 65 cm. Given the significant size difference, otters would be expected to hold a dominant competitive advantage over mink, enabling them to essentially bully them out of their territories or away from their food sources [4] [12]. Unfortunately, this is frequently not the case – many sites in the UK show a coexistence of otters and mink rather than competitive exclusion (we’ll discuss why later). All to say, the negative environmental impacts of American mink aren’t seen through direct competitive interaction with otters, rather through the direct predatory impacts on a variety of prey species.

Impact on Naïve Prey
The small build of the mink actually contributes to one of their most devastating impacts – their predation on the UK’s endangered water voles [23]. The mink is small and agile enough to invade the burrows of the voles, chasing them into their dens through the underwater entrances that deter most of the voles native predators. Water voles, like many other native species, are considered “naïve prey” for the mink [22] – they have not evolved natural defences or behaviours to evade this newly introduced predator, making them easy targets. This inability to respond to new threats can have dramatic consequences for populations already weakened by habitat loss and other pressures [18]. What’s more, the aggressive prey drive of the mink leads them to kill more than they consume, which has led to the eradication of entire local vole populations.

*Water voles are Britain’s most rapidly declining mammal and predation by American mink is a key contributing factor to their decline. Photo credit: Alan Ross*

Diet, Habitat, and Adaptability
While otters tend to have a more specialized diet focused on fish, mink are opportunistic generalist predators [6] [9]. They can hunt a wide variety of prey, including birds, amphibians, fish, rabbits, rodents, crayfish, domestic fowl and more, giving them a significant adaptive edge over otters. This dietary flexibility allows mink to thrive in diverse habitats and conditions, while otters are more limited in their prey choices. The otter needs a river with a good fish population, whereas the mink can find food just about anywhere. The specialized fish diet of the otter also makes them more susceptible to aquatic pollutants [7] [8] – if a river becomes contaminated with toxic chemicals, so too does the otter’s food source, while mink can sustain themselves on terrestrial prey and avoid the contaminant.

Reproduction and Fecundity
The American mink exhibits an “r-selected” or “high output” reproductive strategy, which is typical among invasive species and contributes to their rapid population growth. Effectively this means the mink has higher fecundity (reproductive rate) compared to otters, so they can produce more offspring in a shorter time frame. While both species reproduce once a year, mink typically produce 4–6 kits per litter, compared to the otter’s 1–3 cubs. Additionally, mink can breed as early as one year old, while otters take 2–3 years to reach sexual maturity. Juvenile mortality is high for both species – as high as 50% before reaching maturity for both mink and otters, by some estimates [10] – and under these conditions the r-selected / high output reproductive strategy of the mink proves advantageous.

As well as the high fecundity, mink have a number of traits which make their reproduction adaptable to changing conditions. They’ve been shown to adjust their litter size and breeding times in response to changing population density [2] or prey availability [5]. They also have a rather unique capability for polyamorous breeding, where female mink can sire a single litter from multiple different males she has mated with [3]. These traits make the mink a particularly resilient invader as they can easily respond to changing conditions and “bounce back” after population control efforts.

American mink are opportunistic predators with high reproductive rates which makes them highly successful invaders. Their small size means they can enter burrows of vulnerable native wildlife like water voles. Photo credit: *Marc Evans, Wikimedia Commons.*

Summary
The comparison between the American mink and the Eurasian otter gives an insight into the mink’s invasive success in the UK. Their high fecundity, adaptability, and aggressive predation make them a serious threat to native ecosystems. While both species face challenges from habitat loss and pollution, mink’s ability to thrive under these conditions compounds the pressure on vulnerable species like otters and water voles. Efforts to control mink populations must be sustained and strategic to protect native wildlife from further declines.

References

[1] Fraser, E.J., Harrington, L.A., Macdonald, D.W. and Lambin, X. (2018). Control of an invasive species: the American mink in Great Britain. Oxford Scholarship Online. Oxford University Press. doi:https://doi.org/10.1093/oso/9780198759805.003.0016.

‌[2] Melero, Y., Robinson, E. and Lambin, X. (2015). Density- and age-dependent reproduction partially compensates culling efforts of invasive non-native American mink. Biological Invasions, 17(9), pp.2645–2657. doi:https://doi.org/10.1007/s10530-015-0902-7.

[3] Thom, M. D., & Bagniewska, J. (2015). Biology, ecology, and reproduction of American mink Neovison vison on lowland farmland. Wildlife conservation on farmland: conflict in the countryside, 2, 126.

‌[4] Macdonald, D.W. and Harrington, L.A. (2003). The American mink: The triumph and tragedy of adaptation out of context. New Zealand Journal of Zoology, 30(4), pp.421–441. doi:https://doi.org/10.1080/03014223.2003.9518350.

‌[5] García-Díaz, P., & Lizana, M. (2013). Reproductive aspects of American minks (Neovison vison) in central Spain: Testing the effects of prey availability. Mammalian Biology, 78(2), 111-117.

[6] Bonesi, L., & W. Macdonald, D. (2004). Differential habitat use promotes sustainable coexistence between the specialist otter and the generalist mink. Oikos, 106(3), 509-519.

[7] Mason, C.F. and MacDonald, S.M. (1989). Acidification and other (Lutra lutra) distribution in Scotland. Water, Air, and Soil Pollution, 43(3-4), pp.365–374. doi:https://doi.org/10.1007/bf00279202.

‌[8] Androulakakis, A., Alygizakis, N., Gkotsis, G., Nika, M.-C., Nikolopoulou, V., Bizani, E., Chadwick, E., Cincinelli, A., Claßen, D., Danielsson, S., Dekker, R.W.R.J., Duke, G., Glowacka, N., Jansman, H.A.H., Krone, O., Martellini, T., Movalli, P., Persson, S., Roos, A. and O’Rourke, E. (2022). Determination of 56 per- and polyfluoroalkyl substances in top predators and their prey from Northern Europe by LC-MS/MS. Chemosphere, 287, p.131775. doi:https://doi.org/10.1016/j.chemosphere.2021.131775.

‌[9] Wise, M.H., Linn, I.J. and Kennedy, C.R. (2009). A comparison of the feeding biology of Mink Mustela vison and otter Lutra lutra. Journal of Zoology, 195(2), pp.181–213. doi:https://doi.org/10.1111/j.1469-7998.1981.tb03458.x.

‌[10] Harrington, L.A., Birks, J., Chanin, P. and Tansley, D. (2020). Current status of American mink Neovison vison in Great Britain: a review of the evidence for a population decline. Mammal Review, 50(2), pp.157–169. doi:https://doi.org/10.1111/mam.12184.

[11] Bradshaw, A. V., & Slater, F. M. (2002). A postmortem study of otters (Lutra lutra) in England and Wales. Bristol, UK: Environment Agency.

[12] Erlinge, S. (1972). Interspecific relations between otter Lutra lutra and mink Mustella vison in Sweden. Oikos, 327-335.

[13] Zych, M. (2007). On flower visitors and true pollinators: the case of protandrous Heracleum sphondylium L.(Apiaceae). Plant Systematics and Evolution, 263, 159-179.

[14] Stewart, F., & Grace, J. (1984). An experimental study of hybridization between Heracleum mantegazzianum Somm. & Levier and H. sphondylium L. subsp. sphondylium (Umbelliferae). Watsonia, 15, 73-83.

‌[15] Pyšek, P., Cock, M. J., Nentwig, W., & Ravn, H. P. (2007). Master of all traits: can we successfully fight giant hogweed?. In Ecology and management of giant hogweed (Heracleum mantegazzianum) (pp. 297-312). Wallingford UK: CABI.

[16] Roberts, H. A. (1979). Periodicity of seedling emergence and seed survival in some Umbelliferae. Journal of Applied Ecology, 195-201.

[17] Jelbert, K., Stott, I., McDonald, R. A., & Hodgson, D. (2015). Invasiveness of plants is predicted by size and fecundity in the native range. Ecology and Evolution, 5(10), 1933-1943.

[18] Doherty, T. S., Dickman, C. R., Nimmo, D. G., & Ritchie, E. G. (2015). Multiple threats, or multiplying the threats? Interactions between invasive predators and other ecological disturbances. Biological Conservation, 190, 60-68.

[19] Bogusch, P., Vojtová, T., & Hadrava, J. (2023). High abundance but low diversity of floral visitors on invasive Heracleum mantegazzianum (Apiaceae). NeoBiota, 86, 193-207.

[20] Buttenschøn, R. M., & Nielsen, C. (2007). Control of Heracleum mantegazzianum by grazing. In Ecology and management of giant hogweed (Heracleum mantegazzianum) (pp. 240-254). Wallingford UK: CABI.

[21] Gioria, M., & Osborne, B. A. (2014). Resource competition in plant invasions: emerging patterns and research needs. Frontiers in Plant Science, 5, 501.

[22] Anton, A., Geraldi, N. R., Ricciardi, A., & Dick, J. T. (2020). Global determinants of prey naiveté to exotic predators. Proceedings of the Royal Society B, 287(1928), 20192978. [23] Aars, J., Lambin, X., Denny, R., & Griffin, A. C. (2001, August). Water vole in the Scottish uplands: distribution patterns of disturbed and pristine populations ahead and behind the American mink invasion front. In Animal Conservation forum (Vol. 4, No. 3, pp. 187-194). Cambridge University Press.

Top tips for getting started with Tracks, Trails and Signs.

James Symonds, Project Officer, Scottish Invasive Species Initiative
July 2021

Being able to recognise animal footprints is essential in our American mink monitoring work. As the monitoring rafts we use record the prints of visiting animals on a clay pad being able to correctly distinguish a mink from an otter print can be the difference between a successful mink capture and wasting our time. But, for me, animal tracking is so much more than that – it’s a glimpse into the secret world of the animals around us.

Having a basic understanding of animal tracks and signs can transform time spent in the outdoors from catching a simple breath of fresh air into a fascinating adventure of intrigue and mystery. But be warned – it’s addictive! I have lost count of the number of hours spent investigating some a patch of sand on a riverbank or examining around a tree stump looking for clues.

Most wildlife is cautious of humans, often with good reason, so the likelihood of seeing animals out and about is often low. The time of day, the time of year and the type of weather can also affect what you are likely to see. But, by looking out for animal tracks and signs, you can build a picture of what animals live in the area, and what they’ve been up to. You might not see a pine marten or a tawny owl by day but the print or pellet you find can confirm their presence and inform a suitable place for an evening spotting session or trail camera placement. At the end of the day though, I get a buzz just knowing that these animals are out there.

Tracks and trails

Animals move about constantly within their habitats – particularly in the daily search for food – and when they do, they leave behind tracks (footprints) or trails (paths). A good clear track can give an instant animal identification or provide a good idea of the size and type of the animal in the neighbourhood.

Trails can also give a good idea of an animal or its size but can be misleading – popular routes are often used by many different species. However, they are always worth following in search of tracks and other signs en route.

Tracks and Trails – what will they reveal…?

Top tips for identifying that track

Use a field guide
It takes experience and practise to know what it is you are seeing – so take out (and use!) a field guide. If you forget take a photo of the track and have a look at the guide when you get home.

Look for the features in the print
How many toes? Do you see claws? What shape is the pad? These type of track features in combination help to eliminate species from your enquiries and guide you to the likely suspect.
Look at the top row of images below; Left – four toes with claws, Centre – five toes with claws, Right – four toes no claws

Note the size of the print
Size is important. If you don’t have a ruler with you, take a photo with something in for scale e.g. a key or coin and work out the size later.
Bottom row; Left – less than a 1p piece, tiny! Centre – several £1 coins wide with distinctive claw marks.

Are you seeing front or rear feet?
Often a mammal’s fore and hind feet are shaped differently and leave different prints. For example, a rodent may have a different number of toes on the fore and hind feet. Perhaps you are seeing two types of prints but these can be from the same animal – so take a note of each print features and size.
Bottom row: Right – one animal but hind feet larger and appear in front of the fore feet

^{Top row (L to R): Dog, Otter, Cat. Bottom row: Water vole, Badger, Squirrel}

Remember – when looking at prints you should take ground conditions into account. A soft substrate e.g. sand, silt, clay or snow is more likely to give a nice clear full print with all features visible – just like in the books! However, a hard substrate e.g. firm mud may result in a partial print – perhaps only showing some of the toes or omitting claw marks and so lead you to a false identification. So, take what you see with a pinch of salt – the print itself might be misleading!

Tracks tell a story

Usually where there is one print there’ll be more, so have a look at the arrangement of the prints. Animals move with different gaits – walking, trotting, running, bounding – each method of travel leaves a specific ‘print pattern’. This tells us how the animal was moving, but often the fore and hind prints overlap each other so recognising gaits comes with practice and experience!

There may be more than one species of animal or bird track present – this can be where the detective work really starts. Which animal was there first? Is one set of prints on top of the other? Are you seeing a predator and prey? And it’s always worth following multiple tracks to see if they tell a story – they might end in a pile of feathers and make it easy to deduce what went on at the scene!

*Looks like there was a party here! How many different prints can you spot?*

Feeding signs

I was once told that tree stumps are either a table or a toilet! This couldn’t be more true.

Tree stumps are great places to look for feeding signs. There are a myriad of common feeding signs but have a look for some of these –

Stripped pine cones
Most likely a squirrel or mouse if on a ‘table’ – but don’t discount birds like woodpecker or crossbill.

Nibbled nuts
Mice and voles make a fairly neat hole edged with teeth marks, whereas a ragged hole with rougher edges and peck marks around is more likely to be a bird like great tit or woodpecker. A nut split in half is the work of a squirrel – look for the little hole at the top which it gnaws first.

Damaged bark
The biggest clue here is in the height of the barking. If it’s a few feet up the tree it’s a fair bet it’s the result of deer (or sheep). If nearer ground level then think smaller mammals and rodents – rabbits, voles or beaver.

Nibbled trees
The nutritious and juicy shoots and tips of small trees are often preferentially nibbled by grazers. This is usually the work of roe deer – but don’t discount other herbivores like hares.

Bird remains and feathers
If you find the remains of a bird with practise you’ll soon learn the differences between the kill of a predatory mammal (head bitten off and eaten, feathers bitten off in clumps, crushed bones) and of a bird of prey (beak and skull lying around, feathers plucked and scattered, breast meat eaten).

Pellets
Many birds cough up pellets after feeding containing the undigested and indigestible bits of their prey such as fur, feathers, bones and insect cases. As well as owls, all birds of prey, gulls and crows all produce pellets. Dissecting a pellet is easy and provides a great insight into what the bird has eaten eating to a whole other world of mini skull and jawbone identification.

Feeding signs of predatory mammals are rarely found as small prey is generally eaten whole at the kill location and larger prey is usually taken back to a den or sheltered feeding site for more leisurely and safer consumption.

Poo!

Cause and effect and all that. Animals that leave feeding signs will inevitably also leave droppings, or more accurately – scat! Droppings consist of the indigestible parts of food, such as fur, feathers, bone, chitin, plant matter, mucous and lots of bacteria.

All this excrement is different, identifying features include:

Size
Note the size of the dropping but be aware that this is not always a reliable indicator. Size is dependent to some extent on the animal’s age and can also be affected by the composition of food in the diet.

Shape
Smooth or crinkly, straight or twisted, blunt or tapering? All helpful to note. At first glance a rabbit dropping looks quite similar to a roe deer’s but look again. The rabbit dropping is round and the deer’s is ‘tic-tac’ shaped with a little pinch at the end.

Colour
This is very influenced by what the animal has eaten. For example, it will be very obvious if a bird or mammal has been eating berries!

Smell
Fresh mammal droppings in particular have a strong scent – often “enhanced” by the addition of scent from anal glands. Scent is a helpful identifying feature, but having a good sniff can be a bit of a sensory risk! It might be sweet and vaguely pleasant e.g. otter (jasmine tea / fishy) or badger (musky) or it could be pretty foul e.g. mink (sharp and repellent) If you’re feeling brave – have a sniff!

Content
The contents of the dropping won’t always help you identify the animal – but will tell you what the animal has eaten. Remember, an animal’s diet may change seasonally with the availability of food. Do you see bones, fur, fish scales, grass?

Position
Some animals will deposit droppings in specific places – a badger digs a small hole, known as a latrine, and repeatedly uses it. Both otter and mink will mark a territory by leaving spraint on a prominent riverside rock.

Other signs

Every animal needs somewhere to live or lie up – so another often easily spotted sign of animal presence are their homes and holes.

It’s always worth a glance into the trees to see if there are signs of nests or dreys or excavated holes in trunks. Underfoot look out for holes or burrows dug into the ground. Some residents can be easily deduced – a badger sett for example is large and quite distinctive. But remember, holes may have had multiple different occupants over the years or may be abandoned so the animal who originally made the residence may not be the inhabitant now. Sometimes, of course, there is no hole and nothing more than a patch of flattened grass reveals an otter resting spot.

There are many other indicators of animal presence – sounds, smells, scrapes, feathers and fur and hair are other great indicators. A walk along a fence will often uncover fur snagged on wire where an animal has passed under, over or through. There are signs everywhere you look, believe me.

Give it a go

So why don’t you get outdoors and give it a go? Move slowly and open your eyes, ears and nose to the whole environment around you – you’ll be surprised what you can find. Your walks may take a little longer but that’s a good thing right?

I cannot emphasise enough the importance of a good field guide. I always carry ‘Animal Tracks and Signs’ by Bang and Dahlstrom – an excellent resource. The Field Studies Council also produce a huge range of excellent (and compact) fold out guides which I highly recommend.

Finally, another mantra passed on to me when it came to tracks and signs and which I always keep in mind is that ‘Common things happen most commonly’. Your imagination and enthusiasm can run away with you at times so before declaring you are on the trail of a mythical beast from ancient folk lore just have another look, consider the context and you may come to conclude it is perhaps just a very large fox that has gone before you!

Now enough reading, get outside, start collecting chewed cones, smell some animal droppings and have some fun!

For more information about mink monitoring rafts and the work of the Scottish Invasive Species Initiative visit our website www.invasivespecies.scot

Trail cameras – our secret agents in the field

Jack Farge, Project Officer, Scottish Invasive Species Initiative
September 2020

Trail cameras are handy gadgets that we’ve found increasingly useful here at the Scottish Invasive Species Initiative – so handy in fact that we thought we’d like to tell you a bit about how we use them and what they show us.

The cameras are fixed in place and are triggered by motion sensors which makes them useful for collecting footage of elusive animals such as American mink – a non-native invasive species that we are trying to locate and trap – which we otherwise wouldn’t see. Day or night, rain or shine, our trail cameras are on the job!

Mink mysteries
Our first step in mink monitoring uses a simple, low tech method which can be widely rolled out – the mink raft – this relies on an extensive network of dedicated volunteers to confirm the presence or absence of mink across our project area using these floating rafts. Our fabulous volunteers look after these rafts which consist of a tunnel, with a clay pad inside, to collect the footprints of mink, or any animal, that walks through the tunnel (left image below). Where the presence of mink is confirmed we place live-capture traps onto the raft (right image below) and see if we can catch the mink – which are then humanely dispatched. Mink are naturally curious and usually check out the tunnels on their own accord but they are also sneaky and wily and occasionally they taunt and deceive us – which is where trail cameras come in.

Capturing video footage of mink can provide an insight into their behaviour and help us identify why – even though we know mink are present – they are not venturing into our traps. The raft/trap unit could be positioned on the wrong riverbank or pointing downstream when it would be better pointing upstream – whatever the issue sometimes the trail camera can help us solve the mystery.

Click video to watch (on YouTube) or scroll to bottom of article

We also have had to solve the case of the disappearing bait! We couldn’t work out how bait kept disappearing from inside the trap without the trap being triggered and the door closing! Trail camera to the rescue – it turned out that an otter was sneaking in and having a nice snack on the bait while it held the trap open with its large back!

Snapping Sheep
Trail cameras are also proving really useful at our sheep trial site at Macduff where we are working with a local farmer and the University of Aberdeen to see how best sheep can be used to control Giant hogweed through a managed grazing regime. We’ve installed several cameras around the site which allow us to monitor the sheep’s behaviour, without human influence, by capturing videos of the sheep in grazing action. We are also using trail cameras to gather a visual record of the impact of the sheep by capturing time lapse footage of their grazing progress each day.

What else is out there?
Sometimes it isn’t just mink we find. One of our mink raft volunteers recently asked to borrow a trail camera after suspecting water voles were in the area. Water voles are one of our most threatened native mammals, largely due to mink predation, so it is great to see if they are making a comeback in areas where we are controlling mink. We were happy to lend a camera as gaining familiarity with these gadgets is a great skill for volunteers to learn as well as providing great images for the project. She didn’t get water voles on film but instead found something even rarer, this amazing footage of a family of Scottish wildcats! (N.B. Later confirmed as hybrid wildcats).

Such footage of our native wildlife is really useful and valuable; it can be important for other conservation projects, we can use it on social media to help raise awareness of our native wildlife and it can help engage people with their local environment. We’ve also found that when working in schools showing a class of children video footage of an American mink and an otter is not only helpful in explaining the difference between the two species, but also great at grabbing and focussing their attention!

You can watch more wildlife clips on the Wildlife Watcher page on our website or on our YouTube channel.

Give it a go!
If you’ve got your own trail camera or can borrow one and would like to learn more about how and where to set it, check out our helpful hints in the Alien Detectives ‘Caught on Camera’ activity. If you get some animal footage you’d like us to see and share then get in touch with us at the email address below – we’d love to see what you find!

If you’d like to find out more about our mink control project or are interested in monitoring a mink raft find out more at www.invasivespecies.scot or contact us on sisi@nature.scot