# A review of methods to estimate the abundance of terrestrial carnivores using field signs and observation

> How do you count animals that hide by day and roam by night? This review weighs up the ways researchers estimate carnivore numbers without catching them, from footprints on dusty roads and droppings to DNA, howling surveys, spotlights and camera traps. Again and again it finds that the skill of the person reading the signs matters, and that any index is best checked against a population of known size.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2001-wilson-delahay-review-methods-estimate-abundance/

## Citation and access

- **Authors:** Gavin J. Wilson and Richard J. Delahay
- **Year published:** 2001
- **Journal or source:** Wildlife Research
- **Full citation:** Wilson, G. J. and Delahay, R. J. 2001. A review of methods to estimate the abundance of terrestrial carnivores using field signs and observation. Wildlife Research 28(2): 151-164.
- **DOI:** 10.1071/WR00033
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.1071/WR00033

## Tags

- **Species:** Mammals > African wild dog; Mammals > American black bear; Mammals > American marten; Mammals > Banded mongoose; Mammals > Bobcat; Mammals > Brown bear; Mammals > Canada lynx; Mammals > Cheetah; Mammals > Coyote; Mammals > Dingo; Mammals > Egyptian mongoose; Mammals > Eurasian badger; Mammals > Eurasian otter; Mammals > Feral cat; Mammals > Ferret; Mammals > Fisher; Mammals > Grey fox; Mammals > Grey wolf; Mammals > Kit fox; Mammals > Leopard; Mammals > Lion; Mammals > Mountain lion; Mammals > North American river otter; Mammals > Pine marten; Mammals > Raccoon; Mammals > Raccoon dog; Mammals > Red fox; Mammals > Small Indian mongoose; Mammals > Small-spotted genet; Mammals > Snow leopard; Mammals > Spotted hyena; Mammals > Stoat; Mammals > Suricate; Mammals > Tiger; Mammals > Wolverine
- **Tracking:** Burrows; Hair; Individual identification; Paths; Scat; Sign surveys; Snow tracks; Track counts; Tracking; Tracks; Tracks and signs identification; Trailing
- **Behaviour and ecology:** Behaviour; Communication; Denning; Movement
- **Methods and technology:** Aerial surveys; Camera traps; Capture-mark-recapture; Detectability; Direct observation; Distance sampling; DNA; Hair sampling; Literature review; Population estimation; Population trends; Power analysis; Radio telemetry; Road transects; Survey costs
- **Data type:** Review
- **Observer qualification:** Not needed
- **Discipline:** Population trends; Wildlife tracking
- **Year published:** 2001

## Detailed keywords

- **Species:** Studied: terrestrial carnivores in general, through published case studies. Named examples: mountain lion (Felis concolor; F. c. californica), European genet (Genetta genetta), kit fox (Vulpes macrotis), raccoon dog (Nyctereutes procyonoides), banded mongoose (Mungos mungo), Eurasian badger (Meles meles), Canada lynx (Lynx canadensis), small Indian mongoose (Herpestes javanicus), feral ferret (Mustela furo), stoat (Mustela erminea), European otter (Lutra lutra), meerkat (Suricata suricatta), snow leopard (Panthera uncia), dingo (Canis familiaris dingo), river otter (Lutra canadensis), feral cat (Felis catus), red fox (Vulpes vulpes), gray fox (Urocyon cinereoargenteus), lion (Panthera leo), leopard (Panthera pardus), hunting dog (African wild dog, Lycaon pictus), coyote (Canis latrans), lynx, bobcat (Felis rufus), raccoon (Procyon lotor), fisher (Martes pennanti), American marten (Martes americana), black bear (Ursus americanus), pine marten (Martes martes), Pyrenean brown bear and grizzly bear (Ursus arctos), wolf (Canis lupus), wolverine (Gulo gulo), spotted hyena (Crocuta crocuta), cheetah, Egyptian mongoose (Herpestes ichneumon), tiger (Panthera tigris), civets. Prey: snowshoe hare and moose appear only in cited titles.
- **Location and habitat:** A review with no study area of its own. Case studies come from many places, including Arizona and Florida (USA), western USA, the Yukon (Canada), western Canada and Alaska, central Australia, Namibia, Kruger National Park (South Africa), the Serengeti (Tanzania), the Himalayas, the Pyrenees, Scottish woodlands, England, Britain, Ireland and the Shetland Islands. Habitats mentioned include dirt roads, sand, snow, lakesides, riverbanks, coastal habitat, forest and open plains.
- **Topics:** absolute abundance, population density and relative abundance (indices); complete versus incomplete counts; field signs versus observation; track counts along transects (dirt roads, sand, snow); track stations (sooted plates, smoothed road strips); scent stations and attractants; faecal (scat) counts, standing crop and accumulation rate; defaecation and decay rates; molecular scatology (DNA from faeces) and hair snares; auditory indices (wolf howling surveys); counting dens, setts and holts; direct observation, drive counts and photographic identification; call-in (playback) surveys for lions and hyenas; aerial surveys and following wolf tracks from the air; spotlight counts; thermal imaging; camera traps and video; survey design, confounding factors (season, habitat, weather, substrate), validation and calibration against known populations; the value of skilled fieldworkers and differences between observers.
- **Statistics or models:** None
- **Data type:** Review of published studies (no new field data). Manuscript received 14 April 2000, accepted 16 March 2001. Small citation mismatches in the paper: Ballard et al. is cited as 1993 in the text but listed as 1995 in the references; Becker et al. (1998) is listed with volume 92 of the Journal of Wildlife Management.

## Synopsis

### 1. What they did

Carnivores are hard to count. Many are secretive, active at night and range over large areas, and they live in very different social systems, from solitary animals to pairs to large groups. Trapping animals often enough to estimate numbers can be impractical, labour-intensive and very expensive.

The authors reviewed field methods for estimating and monitoring the abundance of terrestrial carnivores without capturing them. They grouped the methods into two families:

- Field signs: track counts along transects, track stations (with and without scent lures), counts of droppings, DNA from droppings and hair, howling and other calls, and counts of dens, setts and holts.

- Observation: direct counts, call-in (playback) surveys, aerial surveys, spotlight counts at night, thermal imaging, and remote cameras and video.

For each, they described how it works, gave case studies, and discussed its strengths, weaknesses and costs.

### 2. What they found

Field signs in general

- Sign-based methods assume that the amount of sign relates in some way to the number of animals. They are mostly used as indices, to compare places or follow trends over time, rather than to give actual numbers.

- Results depend on the skill of the fieldworkers. The authors point to Stander et al. (1997) as showing the value of field craft, and say such skills are likely to raise detection and interpretation.

- Season, habitat, weather, substrate, and the sex and age of animals can all change how much sign is found, separately from how many animals there are. These effects are easier to control when following one place over time than when comparing places.

Tracks

- Track counts are a relatively cheap way to follow trends, and several species can be monitored at once.

- Where individual footprints can be told apart, by highly skilled fieldworkers (Stander et al. 1997) or by measurements from photographs of tracks, actual numbers can be estimated.

- Some track indices matched known populations well: road-transect track counts for lion, leopard and hunting dog in Namibia were a function of true density, and snow-track counts of coyotes and lynx in the Yukon mirrored other population estimates. An earlier lynx study with fewer surveys and no covariates found a poor match.

- Mountain lion tracks were easier to detect on roads with good dust cover, and roadside habitat changed fox track counts regardless of density. Choosing transects with ecology in mind more than doubled the chance of finding tracks in one study.

- Scent stations gave mixed results when checked against known populations, and lures may attract some animals (by age, sex or status) more than others. For dingoes, track plots without lures gave a more reliable index.

Droppings and DNA

- Counts of droppings can give relative abundance; actual numbers need defaecation and decay rates, and the authors call this an impractical goal for most carnivores. Fox scat counts dropped after rain, and otter spraint numbers swung widely while populations were stable, probably because of seasonal and habitat changes in scent marking.

- DNA from droppings and hair can identify individuals. Coyote numbers from faecal DNA compared well with trapping, and brown bear numbers in the Pyrenees from faecal and hair DNA closely matched an established monitoring scheme based on identifying tracks. Fresh samples, good storage and checks for laboratory errors are essential.

Calls and dens

- Wolf howling surveys can count packs but give only a crude population estimate, and one survey overestimated pack density.

- Den counts work when the number of animals per den is known; counts of otter holts in Shetland were linearly related to the number of resident males. Badger group size varies so much that converting sett counts into badger numbers carries a large potential error.

Observation

- Playback of prey distress calls and lion calls gave a lion estimate within 1% of a photographic count, though responses varied with season and prey abundance.

- From the air, wolf tracks in fresh snow were followed until the pack was seen and counted. This needs experienced pilot-observer teams.

- Spotlighting sometimes missed carnivores in areas where track plots showed they were present.

- Thermal imaging from an aircraft found all the radio-collared mountain lions known to be in a Florida study area.

- Camera traps can estimate numbers where individuals are recognisable, such as tigers by their stripes, but placing cameras on animal trails can bias results.

### 3. What they concluded

- Many methods exist; the choice depends on the study’s aims and scale, the resources available, the ecology of the target species, and the accuracy needed.

- Where animals can be seen, especially as individuals, observation is likely to be preferred. Where that is impossible or too costly, field signs may be necessary.

- Sign-based indices are probably more reliable for following trends in one place over time than for comparing places.

- Methods should, where possible, be validated against a population of known size or a formal estimate; in practice this is seldom done. Where calibration is not possible, using two or more methods together adds confidence.

- Methods based on field signs are especially prone to differences between observers. Skilled fieldworkers are a highly valuable resource, while large surveys with many inexperienced staff should be kept simple enough for consistent recording.

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

The authors did no fieldwork; tracking is a main subject of the review. They discuss studies that used footprints along dirt roads and in sand and snow, prepared track stations, scats and spraints, hair, trails and paths, and dens, setts and holts. Trailing appears in the aerial wolf surveys, where tracks in snow were followed from the air until the pack was found. They note that identifying individual animals from their tracks is sometimes possible with highly skilled fieldworkers, citing Stander et al. (1997), and that a Pyrenean brown bear monitoring scheme was based on identifying tracks.

### 6. Other technologies, skills or innovations

- Genetic fingerprinting (microsatellite DNA) from droppings and hair, with rarefaction and capture-recapture analysis

- Glue-plate and baited hair snares

- Track measurements from photographs to identify individual mountain lions

- Playback of recorded calls to draw lions and hyenas into view

- Spotlights, night-vision and aerial thermal imaging

- Camera traps triggered by trip lines, plates, photic cells or infra-red beams, and remote video

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

- Reliable abundance estimates are basic to conservation, research and management, whether the goal is to increase an endangered population or reduce a pest one.

- Survey design should take account of season, habitat and weather, either by standardising surveys or by recording these as covariates.

- Large increases in survey effort often give only small gains in the power to detect change, so effort should be planned, for example with power analysis.

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

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

- The review repeatedly names the skill of the fieldworker as a source of variation in sign surveys, and calls skilled fieldworkers a valuable resource that is often overlooked when money is short. This supports testing and reporting observer skill in track and sign studies.

- Several of the strongest results in the review rest on reading tracks: track counts that matched known lion, leopard and wild dog densities in Namibia, wolf packs found by following tracks from the air, and a brown bear monitoring scheme based on identifying tracks that agreed with DNA results.

## Cite this summary

Lawrence, K. 2026. Summary of: A review of methods to estimate the abundance of terrestrial carnivores using field signs and observation (Wilson and Delahay, 2001). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2001-wilson-delahay-review-methods-estimate-abundance/