C-DRONE GUIDE · 7 AUGUST 2026
Vole Damage Detection in Grassland by Drone: Multispectral Mapping and Price
Twenty-two million euros in losses in a single year, across 60,000 hectares of grassland: that is the toll recorded in Franche-Comté during a water vole population peak — a burrowing rodent capable of destroying up to 6 tonnes of dry hay per hectare when an infestation is not brought under control in time. The water vole (Arvicola terrestris) breaks out in cycles of 5 to 7 years in mid-mountain grasslands, and how well the fight against it works depends almost entirely on how early it is detected — before burrows and molehills colonise the whole plot. Regional chambers of agriculture and FREDON plant-health bodies have spent several years trialling multispectral drone mapping to spot these outbreaks as soon as they appear, with results already applied in the field. Here is the method, the regulatory framework for control measures, and the price of a mission in 2026.
Published on 7 August 2026, reviewed on 29 August 2026 — regulations in force as of August 2026.
A cyclical pest that costs livestock farmers dearly
The water vole is a burrowing rodent that lives under the grassland year-round, feeding on roots and causing a distinctive soil collapse marked by the mounds of earth it pushes to the surface. Its population dynamics are cyclical: after a low-density phase, numbers explode over 2 to 3 years before collapsing again, a cycle that repeats every 5 to 7 years in mid-mountain grasslands — the Massif Central, the Jura and Franche-Comté foremost among them. A landmark study published in 2000 in Landscape Ecology by Fichet-Calvet, Pradier, Quéré, Giraudoux and Delattre, carried out over eight years in the Doubs département, established that the composition of the farmed landscape — the share of permanent grassland, plot size and clustering — directly influences the risk and scale of outbreaks (see the study on Google Scholar).
On the ground, forage losses can reach 30 to 80% depending on the plot and the year, up to 6 tonnes of dry hay per hectare in the most severe cases; in Franche-Comté, a single outbreak peak cost farms nearly €22 million across 60,000 hectares affected. The cost is not limited to forage: soil riddled with burrows is hard to work, difficult to reseed, and poses a risk to livestock and mowing equipment alike.
What a multispectral and thermal drone flight detects
An early-stage infestation gives off discreet signs: small mounds of freshly turned earth, localised yellowing of the grass above the most active burrows, a mosaic-like compaction of the plant cover. Walking the plot, these signals are easily lost in a grassland's natural variability — which is exactly where aerial imagery offers an overview a ground pass cannot match.
A trial run by the Fredon of Franche-Comté and the agricultural-equipment chair at AgroSup Dijon, published in 2020 in the journal Fourrages by Goulamoussène, Perrot, Toumazet, Michelin, Dureau and colleagues, developed a mapping method combining multispectral imagery with dedicated software processing: burrow and mound indices were identified with a claimed precision above 96%, each outbreak returned with precise GPS coordinates (see the study on Google Scholar). In practice, a standard RGB photogrammetric flight already picks out the most visible mounds; adding a multispectral camera sharpens detection of early plant-stress zones, before mounds even become numerous — the same vegetation-index logic detailed in our guide on drone crop water-stress mapping. A thermal pass at the end of the day can complete the analysis by revealing still-active burrow entrances, cooler than the surrounding soil.
The regulatory framework for control: FREDON and prefectural orders
The water vole is listed among the harmful organisms set out in the order of 16 April 2020, issued under France's rural and maritime fishing code. In the regions hit hardest — Bourgogne-Franche-Comté, Auvergne-Rhône-Alpes, Occitanie — a Regional Action Plan (PAR), run and coordinated by the local FREDON body, organises prevention, surveillance and control across the territory. On that basis, the local prefect can make control measures mandatory by order in communes classified as at-risk, requiring any farmer or landowner with affected grassland to implement defined measures: trapping, encouraging natural predation, and adjusting mowing and grazing practices.
Drone mapping fits into this system as an early-detection tool, ahead of a farmer being pushed into a stricter control obligation: spotting a nascent outbreak over a few ares allows a targeted trapping response, markedly cheaper and less constraining than treating a whole plot once the infestation has spread. Some regional FREDON bodies and chambers of agriculture already offer support combining a scouting flight with technical advice; an independent drone provider can also step in as a complement, particularly for large holdings where walking every plot is time-consuming.
Organising the flight: timing, equipment, airspace rules
The most effective window falls just after a mowing pass or at the end of winter, when the plant cover is short: mounds and stress zones stand out far more clearly than during full growth. Repeated monitoring — one flight in spring, a second at the end of summer — makes it possible to track an outbreak's progression from one season to the next and assess how effective the control measures taken in between actually were.
Since grassland usually sits in open rural areas, the mission generally falls under the standard open category framework; checking the Géoportail restricted-zone map nonetheless remains standard practice, particularly in mid-mountain areas where low-altitude military zones sometimes overlap. The provider needs a valid AlphaTango registration and professional liability insurance, as for any agricultural mission; the delivered report needs to be georeferenced so outbreaks detected can be overlaid from one campaign to the next and, where relevant, passed on to the FREDON body under the regional action plan.
The price of a mapping mission in 2026
The price depends on the surface to cover, the number of sensors used (RGB alone, or combined with multispectral and thermal), and the number of passes over the season. Orders of magnitude observed in France in 2026 (excl. VAT):
| Service | Observed price (excl. VAT) |
|---|---|
| RGB scouting flight, one grassland plot (up to 10 ha) | €150 to €350 |
| Multispectral mapping with outbreak-index processing | €300 to €700 depending on surface |
| Additional end-of-day thermal pass | +€100 to €200 |
| Seasonal monitoring (2 to 3 flights, spring/summer/autumn) | quoted, lower per-unit rate |
The comparison that matters is not the price of the flight alone, but the cost of an outbreak detected too late: a few ares treated by early trapping cost markedly less than a whole plot that has to be reseeded after a population peak. Our guide on drone forage biomass estimation details a complementary measurement useful for putting a number on an affected plot's yield loss. Request a quote stating the grassland surface affected, the region, and how advanced the infestation is.
Does a drone replace ground scouting by a FREDON technician? No: it complements it by quickly covering large surfaces; the technician is still needed to confirm the species and advise on the control method.
Is a single flight enough? For early detection, yes; to track how effective the control measures taken have been, a second flight at the end of the season is recommended.
Can the mapping be shared with FREDON or the chamber of agriculture? Yes, provided it uses a standard georeferenced format; some regional action plans actively encourage this kind of reporting.
Does this method also work against the common vole? The common vole (Microtus arvalis), a pest of arable crops, leaves different surface signs; the method transposes but the interpretation thresholds are not the same as for the grassland water vole.
Put it into practice
- Drone aerial thermal imaging: rates and cities covered from €500
- Aerial thermal imaging in Auxerre Bourgogne-Franche-Comté
- Aerial thermal imaging in Mâcon Bourgogne-Franche-Comté
- Aerial thermal imaging in Montpellier Occitanie