# Distinguishing tracks of mink Mustela vison and polecat M. putorius

> Mink and polecat tracks look almost the same, which is a real problem when rafts with clay pads are used to find and trap invasive mink in Britain, where polecats are protected. By measuring footprints from wild animals walking over clay, researchers found that three measurements, mostly about how widely the toes are spread, tell the two apart in more than nine cases out of ten.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2008-harrington-harrington-distinguishing-tracks-mink-mustela/

## Citation and access

- **Authors:** Lauren A. Harrington, Andrew L. Harrington and David W. Macdonald
- **Year published:** 2008
- **Journal or source:** European Journal of Wildlife Research
- **Full citation:** Harrington, L. A., Harrington, A. L. and Macdonald, D. W. 2008. Distinguishing tracks of mink Mustela vison and polecat M. putorius. European Journal of Wildlife Research 54(2): 367–371.
- **DOI:** 10.1007/s10344-007-0145-8
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.1007/s10344-007-0145-8

## Tags

- **Species:** Mammals > American mink; Mammals > European polecat
- **Region:** Europe > United Kingdom
- **Tracking:** Claw marks; Track measurements; Track photographs; Tracking; Tracks; Tracks and signs identification
- **Methods and technology:** Analysis of variance (ANOVA); Geographic Information System (GIS)
- **Data type:** New field data
- **Observer qualification:** Not reported
- **Discipline:** Wildlife tracking
- **Year published:** 2008

## Detailed keywords

- **Species:** Studied: American mink (Mustela vison), an introduced pest species in the United Kingdom (UK) and mainland Europe, and polecat (Mustela putorius), a protected species in the UK. All animals were adults: 12 mink (five males, six females, one of unknown sex) and nine polecats (three males, six females). Mentioned for comparison: stoat (Mustela erminea) and otter (Lutra lutra), whose tracks are easily told from mink tracks by size.
- **Location and habitat:** Upper Thames valley, Oxfordshire, UK. Lowland rivers, where mink are monitored and trapped on floating tracking rafts. Tracks were collected on moist clay in a wooden tunnel designed to simulate a tracking raft.
- **Topics:** telling apart the tracks of similar-sized mustelids; mink and polecat footprints on clay tracking plates; track measurements and ratios (track width, toe pad spacing, claw mark length); claw mark shape; measurement repeatability and error; sexual size differences in tracks; avoiding accidental trapping of protected polecats in mink control; a “rule of thumb” for field use; possible terrestrial tracking plates for polecat surveys. Inconsistencies in the paper: (1) the abstract gives classification success “greater than 90%” and the methods aimed for over 95%, while the recommended three-measurement model scored 97.3% on the development tracks but 93.9% on the test tracks; (2) in Table 1 the three-measurement model’s F value (4.12, df 3,69, p = 0.0095) is far lower than the other models’ (28.67 to 43.23, p < 0.0001) and its degrees of freedom differ, which is not explained; (3) the test dataset should hold 37 tracks (56 minus 35 mink tracks plus 63 minus 47 polecat tracks), but Table 1 reports 32 or 33, with no reason given (possibly missing measurements).
- **Statistics or models:** Linear discriminant function analysis (stepwise removal of variables, Mahalanobis distance D² to test the functions and find outliers, covariance matrices checked for homogeneity); nested analysis of variance (ANOVA) for repeatability and measurement error (Bailey and Byrnes 1990); ANOVA with Tukey’s test for size differences between species-sex groups; 95% confidence intervals and ranges; standard deviations, coefficients of variation (CV) and effect sizes for choosing variables; correlation matrices; t tests with Bonferroni correction. Method broadly follows Zielinski and Truex (1995).
- **Data type:** New field data: tracks from wild mink and polecats trapped in 2005, with a separate test dataset from randomly chosen animals (five mink, three polecats).

## Synopsis

### 1. What they did

American mink are an introduced pest in the United Kingdom (UK) and mainland Europe. They are monitored and trapped using floating rafts fitted with clay tracking plates: when mink tracks appear on a raft, a trap is set there. Mink tracks are easily told from stoat and otter tracks by size, but polecats are a similar size, and their tracks are hard to tell from mink tracks. Polecats are also found on mink rafts, and in the UK they are protected, so trapping them on purpose is prohibited. The authors set out to find a reliable, measurement-based way to tell the two species’ tracks apart.

- Collecting tracks (2005). Wild mink and polecats trapped in the Upper Thames valley, Oxfordshire, were released into a wooden tunnel (0.2 × 0.2 × 2.4 m) over a layer of moist clay, built to imitate a tracking raft but long enough to record several tracks from each animal. A temporary obstruction at the far end encouraged the animals to walk rather than run. All animals were adults.

- Photographing and measuring. Each footprint was photographed with a digital camera beside a ruler. Overlapping tracks, tracks with fewer than three clear toe prints and tracks with poorly defined pads were left out (under 10%). Front and hind, left and right feet were all included and not told apart, so that the method could be used in the field without having to identify which foot made the track. Tracks were measured on screen in ArcMap, a Geographic Information System (GIS) program, to 0.1 mm: 15 measurements of the track and the spacing between its pads, plus eight ratios between them, because the authors expected differences in shape rather than size. They also recorded whether claw marks were present and their shape.

- Checking the measurements. Six measurements were repeated five times on five mink tracks to see how much the same measurement varied.

- Building and testing a formula. Tracks from five mink and three polecats were set aside as a test set. The remaining tracks were used to choose the most useful measurements and build a discriminant function (a formula that sorts a track into one species or the other), which was then tried on the test set.

### 2. What they found

- They collected 56 tracks from 12 mink and 63 tracks from nine polecats. Mean weights: male mink 1,460 g, female mink 840 g, male polecats 1,510 g, female polecats 1,030 g.

- Measurements were repeatable: measurement error was between 1.11% and 5.79%.

- Size alone does not work. Male mink tracks were wider than those of polecats and of female mink, but the ranges overlapped. Males of both species had longer tracks than females, while same-sex mink and polecats had similar track lengths.

- Claw marks: claw marks showed in 74% of mink tracks and 98% of polecat tracks. “Crooked” claw marks, described in earlier work as typical of polecats, were more common in polecat tracks (37%) than mink tracks (3%), but 63% of polecat claw marks looked straight, so claw shape was not a reliable guide.

- Rules of thumb: where long claws show, a distance of more than 6 mm from the top of the middle toe pad to the tip of its claw mark means a polecat; below 6 mm it could be either. A gap of more than 4 mm between the two middle toe pads (d1) suggests mink; below 4 mm it could be either.

- The formula: six measurements together classified 98.6% of tracks correctly, and 100% of the test tracks. The simplest model used only three: overall width across the toes (W1), the gap between the two middle toe pads (d1), and the mean gap between each outer toe and its neighbouring inner toe (d7 and d8). It classified 97.3% correctly, and 93.9% of the test tracks.

- The rule: if 1.70 − 0.75(W1) + 2.43(d1) + 1.85(mean of d7 and d8) is above 0, the track is classed as mink; below 0, polecat.

- What it looks like: mink toe pads are more widely spaced, especially the two middle ones, and the outer toes sit so that mink tracks look much wider for their length than polecat tracks.

### 3. What they concluded

- Three simple measurements can separate mink and polecat tracks on clay tracking plates with high success.

- Clear, sharp tracks are essential. Where polecats are known or suspected, the authors recommend renewing and smoothing the clay often.

- Measurements can be taken in the field with calipers, or from photographs with a ruler, measured later with calipers on prints or with software such as ArcGIS or Photoshop.

- Limits: the formula was built from adult animals walking on clay. The authors do not know how well it works on natural ground or with running animals, and it cannot be used for juveniles (a potential problem only in summer). Further work is needed to include juveniles.

- Being able to recognise polecat tracks suggests terrestrial tracking plates could be developed to survey and monitor polecats, whose current survey methods are limited or very labour intensive. This warrants further attention.

### 4. How tracking was or was not used

The study is about tracks and signs identification: telling mink and polecat footprints apart on clay. The authors measured toe pad spacing, track width and length, and claw marks, tested an earlier qualitative description of claw shape (Sidorovich 1999), and turned the most useful measurements into a formula and two field rules of thumb. No trailing was involved; the species of each track was known because the animals had been trapped.

### 5. Tracker or observer certification

Not reported. The measurements were taken from photographs in software, and their repeatability was checked statistically (measurement error 1.11% to 5.79%), but the paper does not say who measured the tracks or what tracking experience they had.

### 6. Other technologies, skills or innovations

- A long clay-lined tunnel that imitates a mink tracking raft, with a temporary obstruction so animals walk, giving several tracks from each known animal.

- Digital photographs with a ruler, measured to 0.1 mm in ArcMap (ArcGIS 9).

- A separate test dataset from different animals, to check the formula fairly.

### 7. Implications for conservation (from the paper)

- Mink control on rafts depends on correctly identifying mink tracks. Recognising polecat tracks helps avoid trapping polecats, which are protected in the UK, and saves time and effort when starting a mink control programme.

- Tracking plates might become a survey and monitoring tool for polecats.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- The study tested a published identification feature (crooked polecat claw marks) and found it held only some of the time. It is a reminder that a single feature is rarely enough, and that tracks are best read as a whole.

- The key difference is in shape and spacing rather than size: the gap between the middle toes and how widely the outer toes sit. These are features a tracker can learn to see by eye, not only measure.

- The formula comes from walking adults on smooth clay; tracks in mud, sand or snow, or of running or young animals, may not fit it.

## Cite this summary

Lawrence, K. 2026. Summary of: Distinguishing tracks of mink Mustela vison and polecat M. putorius (Harrington and Harrington et al., 2008). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2008-harrington-harrington-distinguishing-tracks-mink-mustela/