# Tracks in snow and population size estimation: the wolf Canis lupus in Finland

> Can counting wolf tracks crossing ski trails tell you how many wolves a country has? Finland compared 20 years of a nationwide winter snow track census with yearly counts of wolf litters and found that the tracks picked up the population’s five-fold rise and later fall, even with fewer than one wolf per 1000 km². The authors also used tracks and daily travel distance to estimate wolf numbers, but caution that wolf tracks are too few to count the population reliably year by year.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2014-kojola-helle-tracks-snow-population-size/

## Citation and access

- **Authors:** Ilpo Kojola, Pekka Helle, Samuli Heikkinen, Harto Lindén, Antti Paasivaara and Marcus Wikman
- **Year published:** 2014
- **Journal or source:** Wildlife Biology
- **Full citation:** Kojola, I., Helle, P., Heikkinen, S., Lindén, H., Paasivaara, A. and Wikman, M. 2014. Tracks in snow and population size estimation: the wolf Canis lupus in Finland. Wildlife Biology 20(5): 279–284.
- **DOI:** 10.2981/wlb.00042
- **Access status:** Hosted (freely available elsewhere)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/2014_Kojola_and_Helle_etal_tracks-in-snow-and-population-size-estimation-the-wolf.pdf

## Tags

- **Species:** Mammals > Grey wolf
- **Region:** Europe > Finland
- **Tracking:** Snow tracks; Track counts; Tracking; Tracks and signs identification; Trailing
- **Behaviour and ecology:** Behaviour; Daily travel distance; Dispersal; Range expansion
- **Methods and technology:** Citizen science; Formozov–Malyshev–Pereleshin (FMP) formula; Global Positioning System (GPS) collars; Linear regression; Population estimation; Population trends; Radio telemetry; Very high frequency (VHF) radio collars
- **Data type:** Existing data
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology; Population trends; Wildlife tracking
- **Year published:** 2014

## Detailed keywords

- **Species:** Studied: wolf, gray wolf (Canis lupus). Snow tracks of about 25 mammal species are recorded in the wider winter census, but only wolf tracks are analysed here. Other species mentioned only through the literature: wolverine (Gulo gulo), brown bear (Ursus arctos), tiger (Panthera tigris) and Andean bear.
- **Location and habitat:** Finland, nationwide, with separate analyses for the eastern wolf management zone (the core area of Finnish wolves, bordering Russia) and the western management zone; a northern management zone and the reindeer husbandry area are also mentioned. Wildlife triangle transects randomly sample forested environments. The population is shared with Russia.
- **Topics:** wolf population monitoring; snow track indices; wildlife triangle scheme (annual winter track census, 12 km triangular transects); track density (crossings per 24 hours per 10 km); counting reproductions (litters) as a population index; comparing two independent monitoring methods; population trends; recovery and decline of a large carnivore; legal harvest and poaching; dispersal; range expansion to the west; converting track density into population density (Formozov 1932, stereology); daily movement distance; low-density, clustered populations. Inconsistencies in the paper: (1) the Results text says track frequency explained 59% of the variation in the eastern zone and 68% nationwide, but Table 1 and the abstract give the reverse (eastern R² = 0.682, entire Finland 0.589); (2) the abstract and Figure 4 give the regression period as 1996–2009, while the Table 1 caption says 1996–2010 with n = 15 years; (3) the yearly decline in litters is given as 11% (2007–2009) in the Results and as 15% per year (2006–2009) in the Discussion; (4) the abstract calls the R² values adjusted, Table 1 does not.
- **Statistics or models:** Linear regression of log-transformed number of litters on the proportion of triangles with wolf tracks in the previous winter (slopes, standard errors, F tests against an intercept-only model, 95% confidence intervals, R²); residuals checked for autocorrelation; smoothed track frequencies for showing trends; conversion of track density to population density using average daily travel distance (Formozov’s formula and stereology).
- **Data type:** Existing data from long-term national monitoring: wildlife triangle winter counts 1989–2010 (17 256 counts, about 200 000 km of transects; counts run 15 January to 28 February, to 15 March in the north); confirmed wolf reproductions 1996–2010 from a volunteer observation network; 125 wolves fitted with VHF and GPS collars 1998–2011. Population-density check pooled 2002–2009.

## Synopsis

### 1. What they did

Large carnivores such as wolves are rare and wide-ranging, which makes them hard to count. In Finland, the official wolf population estimate is based on the number of packs that breed each year: with an average of four pups per litter in early winter, and pups making up about 40% of the population, multiplying the number of litters by ten gives a rough population size.

Finland also runs a separate, long-term winter census called the wildlife triangle scheme. About 1700 permanently marked triangles, each with three straight 4 km sides (12 km in all), randomly sample the country’s forests. About half are counted each winter, usually on skis, and every fresh crossing of about 25 mammal species’ tracks in the snow is recorded. To make sure only fresh tracks are counted, old tracks are covered or marked a day or two before the count, or the count follows a snowfall that has covered all old tracks.

The authors asked whether these two independent methods tell the same story about wolves. For each winter from 1989 to 2010 they worked out the share of counted triangles with wolf tracks, for the whole country and for the eastern and western management zones. They then compared this with the number of litters confirmed each year from 1996, using linear regression.

The litter counts came from a network of about 1700 volunteers who report wolf observations on forms and maps each year (from 1045 reports in 1996 to 5439 in 2006). Territory boundaries from radio-collared wolves (125 wolves collared with very high frequency (VHF) and Global Positioning System (GPS) transmitters during 1998–2011), together with snow tracking by field assistants, were used to avoid counting the same pack twice.

Finally, they tested whether wolf track density could be converted into a population size, using a formula that links track density to animals’ average daily travel distance.

### 2. What they found

The census and the wolves

- From 1989 to 2010, 17 256 triangle counts covered about 200 000 km. Wolf tracks were found in 306 counts, with 832 tracks in total. Where wolves had crossed, a triangle had 1 to 23 wolf tracks.

- From 1996 to 2000, wolves bred only in the eastern zone. Breeding then spread to the western zone.

- The number of litters rose from 4 in 1996 to 25 in 2006, then fell to 13 in 2010 (Figure 2). The breeding population grew five-fold in 10 years, then dropped by 40% in four years.

- Unclear cases, mostly the smallest packs of three or four wolves, made up 6% of potential reproductions (199) and were left out. No pack was found with two litters in one year.

Tracks versus litters

- The smoothed frequency of wolf tracks across Finland rose by 11% a year from 1996 to 2006, then fell by 6% a year from 2007 to 2009. Litters followed the same pattern, rising by 18% and falling by 11% (the Discussion gives the decline as 15% a year for 2006–2009).

- In the eastern zone, the track frequency in the previous winter explained 68% of the variation in the (log-transformed) number of litters, and nationwide 59% (Table 1 and abstract; the Results text swaps these two figures). Both relationships were statistically significant.

- In the western zone, it explained only 38%. The authors suggest this is because fewer litters in the west make the numbers more random.

- This worked even though wolves were very thinly spread: fewer than one wolf per 1000 km² nationwide, and fewer than three per 1000 km² in the eastern zone.

From tracks to population size

- For 2002–2009, south of the reindeer husbandry area, 32 771 km of transects held 552 wolf tracks, and the population estimate averaged 205 wolves. For the formula to balance, wolves would need to travel 25.9 km a day on average.

- This is close to published figures (27 km a day in Poland, and figures from central Italy) and to the authors’ own unpublished collar data.

### 3. What they concluded

- Winter track counts on a fixed, nationwide transect network picked up the major rises and falls in Finland’s wolf population, even at extremely low densities. A clear reason was that the population changed so much during the study.

- The rise (18% a year) matches a legal harvest of 10–20% of the estimated population during 1996–2005. The decline from 2006 to 2009, when legal harvest was below 10% a year, suggests that wolf numbers were mainly controlled by poaching. Dispersal to Scandinavia was too small to explain it.

- Because wolves live in packs, their tracks are clustered, which adds randomness to track counts. Weather and snow conditions may also explain some of the unexplained variation.

- Converting track density to population size seems valid in principle, but annual wolf track numbers are low (a mean of 69 a year in 2002–2009) and strongly affected by chance, so the authors have been reluctant to make yearly population estimates from tracks.

- Track indices may be a sound option when continuous pack-based monitoring is not possible, for example as trend indicators between occasional full counts. Where territories can be mapped and packs snow-tracked every year, track indices do not add essential data.

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

Tracking is central to the study. Volunteers on the wildlife triangle census identify and record fresh snow tracks of about 25 mammal species, including wolves, crossing fixed 12 km transects, and the count of wolf track crossings is the index tested. Separately, field assistants snow-tracked wolves, alongside radio-collar data on territory boundaries, to avoid counting the same pack twice when tallying litters. The paper also discusses converting track density into population density.

### 5. Tracker or observer certification

Not reported. The paper does not say who counts the wildlife triangles or how they are trained, and does not describe the skills of the field assistants who snow-tracked wolves or of the volunteer network. This matters because the index depends on wolf tracks being correctly told apart from those of other species, such as dogs.

### 6. Other technologies, skills or innovations

- A permanent nationwide network of about 1700 triangular snow-track transects, in use since 1989, with a standard way of making sure only fresh tracks (from the last one or two days) are counted.

- VHF and GPS collars on 125 wolves, used to map territories and to measure daily movements.

- A volunteer network of about 1700 people reporting wolf observations on forms and 1:200 000 maps.

- A track-density-to-population conversion (Formozov’s formula, based on stereology) that needs only the average daily travel distance of the species.

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

- Sound monitoring is essential for judging population viability and extinction risk, yet few wolf monitoring methods have been formally tested.

- Track indices from extensive winter transects can show major population trends cheaply where yearly pack counts are not possible, and could be combined with full counts every few years.

- The fall in wolf numbers after 2006 points to poaching as the main control on the population, and cryptic poaching that removes whole packs in late winter may weaken the link between track counts and litters, especially in the west, where people may accept wolves less.

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

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

- The study shows how a simple, standardised snow track count, repeated over many years on fixed routes, can follow the fortunes of a rare carnivore. Its value rests on large numbers of observers reliably recognising wolf tracks in snow, a skill the paper does not describe or test.

- The track-density conversion links two things trackers read directly, how often tracks cross a line and how far animals travel in a day, to the number of animals on the land.

## Cite this summary

Lawrence, K. 2026. Summary of: Tracks in snow and population size estimation: the wolf Canis lupus in Finland (Kojola and Helle et al., 2014). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2014-kojola-helle-tracks-snow-population-size/