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Thermal Drones Detected 22 of 24 Marked European Roe Deer Fawns Before Mowing

European roe deer fawn standing in vegetation and looking toward the camera
Conservation · Management

A field study at the 2,100-hectare Stora Bjurum estate in Västra Götaland, Sweden, tested whether thermal drones could find European roe deer (Capreolus capreolus) fawns before mowing and whether short-distance relocation was followed by short-term survival. During their first weeks, roe deer fawns rely on lying motionless in dense vegetation to avoid predators; the same hiding strategy makes them vulnerable to mowing machinery. Forty fawns were marked during the 2024 field season.

Across 25 mowing events on 19 fields, 24 radio-marked fawns were known to be present before mowing. An independent drone pilot who did not know their locations detected 22 of the 24, or 91.7%. All detections were confirmed on the ground, with no false detections. The two missed fawns were in unusually tall or dense vegetation.

Most marked fawns were found and moved before mowing

Twenty-four fawns were relocated before mowing. For the 23 with complete coordinates, relocation distances ranged from 74 to 293 metres and averaged 167 metres. Twenty-two relocated fawns could be monitored for 4–9 days after their final move, and all remained alive during that period. A follow-up more than a month later documented 12 fawns alive, seven collar drops, two transmitter failures and one mortality of unknown cause; several observations were consistent with mother–offspring reunion.

Relocation did not eliminate all mowing risk

One marked fawn was killed during mowing elsewhere on the estate after moving into a field scheduled for mowing. The authors contrast the single mowing death recorded in 2024 with the landowner’s earlier estimate of about 25 such deaths per year before thermal-UAV scanning was introduced, and describe the 2024 result as a marked reduction in observed mowing-related mortality associated with UAV use.

Sources and image credit

  1. Kjellander, P., van der Heide, P., Ausilio, G., Christensson, M., Hensel, H., Höglund, L., Jarnemo, A., Norström, A., & Rumiano, F. (2026). Thermal-UAV assisted detection and relocation of roe deer fawns in managed grasslands. Wildlife Biology, e01701. https://doi.org/10.1002/wlb3.01701Peer-reviewed Version of Record first published online 20 August 2026. Forty European roe deer fawns were marked in Sweden; an independent UAV pilot detected 22 of 24 radio-marked fawns known to be present before mowing, and all 22 relocated fawns monitored for 4–9 days survived that period.
  2. Kjellander, P., van der Heide, P., Ausilio, G., Christensson, M., Hensel, H., Höglund, L., Jarnemo, A., Norström, A., & Rumiano, F. (2026, February 10). Thermal-UAV assisted detection and relocation of roe deer fawns in managed grasslands [Preprint]. https://doi.org/10.22541/au.177075198.88223885/v1First public version, posted 10 February 2026.

Image: caroline legg / Wikimedia Commons — European roe deer fawn in Dumfries and Galloway, Scotland, 29 May 2023. Representative image for this story; not presented as an animal or scene from the reported study or event. · CC BY 2.0 · Source

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