# Use of Radio Tracking to Improve the Estimation by Track Counts of the Relative Abundance of Red Fox

> How many foxes does a line of tracks in the sand really represent? By radio tracking red foxes in Spain’s Doñana reserve, researchers found that each fox crossed a fence transect up to six times a night, and that simply moving the transect could change the count. Their short study shows how knowing animals’ movements can turn track counts into better estimates of abundance.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/1987-servin-rau-use-radio-tracking-improve/

## Citation and access

- **Authors:** Jorge I. Servin, Jaime R. Rau and Miguel Delibes
- **Year published:** 1987
- **Journal or source:** Acta Theriologica
- **Full citation:** Servin, J. I., Rau, J. R. and Delibes, M. 1987. Use of radio tracking to improve the estimation by track counts of the relative abundance of red fox. Acta Theriologica 32(30): 489–492.
- **DOI:** 10.4098/AT.arch.87-36
- **Access status:** Hosted (freely available elsewhere)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/1987_Servin_and_Rau_etal_use-of-radio-tracking-to-improve-the-estimation-by-track-counts-of-the-relative-abundance-of-red-fox.pdf

## Tags

- **Species:** Mammals > Red fox
- **Region:** Europe > Spain
- **Tracking:** Track counts; Tracking; Tracks; Tracks and signs identification
- **Behaviour and ecology:** Behaviour; Movement
- **Methods and technology:** Descriptive statistics; Population estimation; Radio telemetry
- **Data type:** New field data
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology; Wildlife tracking
- **Year published:** 1987

## Detailed keywords

- **Species:** Studied: red fox (Vulpes vulpes), four adult males radio tracked. Other species mentioned only through the literature: striped skunk, white-tailed deer, wolf (Canis lupus lupus), lynx and snowshoe hare.
- **Location and habitat:** Doñana Biological Reserve (Coto Doñana), southwestern Spain. Homogeneous sand dune habitat, with a 3.3 km straight fence used as the track transect.
- **Topics:** track counts; relative abundance index (foxes per km); correction factor; daily rate at which individuals cross a transect; effect of transect position; movement patterns; overtracking and clearing the census route (sweeping with a device mounted on rollers, or waiting three days after rain); nocturnal activity; non-permanent transects such as ski paths; assumptions of the track count method.
- **Statistics or models:** Descriptive statistics only: mean and standard error of daily crossings (2.86 ± 0.7, 7 periods of 24 hours). Relative abundance = number of trails crossing the transect ÷ average daily crossing rate per fox ÷ transect length in km. A “typical pattern” of daily movement made by averaging each hourly radio location into 25 “activity centers” (after Hayne 1949), with eight simulated transects drawn across it.
- **Data type:** New field data: radio tracking and monthly track counts, December 1984 to February 1985 (late fall and mid winter). A short note (Fragmenta Theriologica). Small numbers: four foxes, seven 24-hour periods (four from one fox), and three track counts; the authors present the counts only as an example. The crossing numbers on the simulated transects are only in Figure 1, which is faintly printed; we read them as between 2 and 6, against 3 on the real fence.

## Synopsis

### 1. What they did

Counting the trails that animals leave where they cross a transect is a common way to estimate the relative abundance of carnivores. These counts usually assume that each animal crosses the transect at a steady daily rate. The authors set out to measure how often red foxes actually cross a transect, and how the way foxes move and where the transect lies affect the count.

- Radio tracking. In the Doñana Biological Reserve, southwestern Spain, they caught four adult male foxes with neck snares and padded steel leg-hold traps, fitted them with radio transmitters and released them where they were caught. They then followed them for seven continuous 24-hour periods (four for one fox, one each for the other three), taking one bearing an hour, and mapped each day’s movements.

- Counting crossings. From the maps they counted how many times a day each fox crossed a straight 3.3 km fence that ran through all four home ranges.

- Track counts. Once a month, from December 1984 to February 1985, they counted fox trails crossing a 1.3 km stretch of the same fence. The day before each count, they cleared the route with a sweep mounted on rollers, or they waited three days after the last rain.

- Testing transect position. They averaged the hourly radio locations into a “typical” daily path of a fox, drew eight evenly spaced imaginary transects across it, and counted how often the path crossed each one.

### 2. What they found

- Each fox crossed the fence between zero and six times a day, on average 2.86 times (standard error 0.7). The foxes crossed about equally often in each direction, suggesting they were resident, and all crossings were at night.

- The track counts found 1 trail in December, 5 in January and 8 in February: 0.77, 3.85 and 6.15 trails per km.

- Dividing by the average daily crossing rate turned these into 0.27, 1.35 and 2.15 foxes per km.

- The number of crossings changed a lot depending on where the transect was placed across the typical daily path (Figure 1 shows between about 2 and 6 crossings on the imaginary transects, against 3 on the fence).

### 3. What they concluded

- How foxes move during the day and where the transect lies both strongly affect the results of track counts. This bias matters most when transects are not permanent or are imaginary lines, such as ski paths.

- Used as they usually are, track counts give only a rough measure of population trends. To do better, the method needs a large sample, knowledge of how often each animal crosses the transect, a cleared route to avoid counting old tracks again, and an assumption that animals are neither drawn to nor put off by the transect (for example a road or fence). This study focused on the crossing rate.

- Radio tracking can provide correction factors for each species, habitat and season, making track counts more reliable and helping to design better surveys.

- The authors acknowledge two weaknesses: only males were radio tracked (although males and females had about the same home range sizes and daily movements in the area, from unpublished data) and there were only a few track counts, used as an example.

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

The researchers counted fox trails crossing a fence transect on sand, after sweeping the route or waiting three days after rain so that only fresh trails were counted. These counts were then corrected with the daily crossing rates measured by radio tracking. The paper does not describe how fox trails were identified or told apart from those of other animals. No trailing was reported.

### 5. Tracker or observer certification

Not reported. The paper does not say who counted the trails or how experienced they were.

### 6. Other technologies, skills or innovations

- Radio transmitters working in the 151 megahertz (MHz) range (Biotrack, England), with one bearing an hour over continuous 24-hour periods.

- A sweep mounted on rollers to clear the census route before each count.

- Combining radio tracking with track counts to turn a count of trails into an estimate of foxes per km.

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

- Correction factors from radio tracking could improve track counts and survey design. This is especially relevant for rare or endangered species, where even small changes in numbers may need particular attention.

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

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

- A count of tracks crossing a line measures how often animals cross that line as well as how many animals there are. Where a transect lies within each animal’s daily range can change the count, even when the number of animals stays the same.

## Cite this summary

Lawrence, K. 2026. Summary of: Use of Radio Tracking to Improve the Estimation by Track Counts of the Relative Abundance of Red Fox (Servin and Rau et al., 1987). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/1987-servin-rau-use-radio-tracking-improve/