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Thermal Binoculars Accounted for 79% of European Hare Detections in a Swedish Monitoring Trial

European hare near Fågelfors in Sweden
Research · Other research

A Swedish pilot study published in 2026 tested whether thermal binoculars combined with distance sampling could improve daytime monitoring of European hare (Lepus europaeus). Researchers surveyed three sites in south-central Sweden five times each between November 2022 and February 2023, walking a total of about 60 km of transects.

A transect is a predefined line or route used to survey an area systematically, with observations, signs or sampling points recorded along it.

They detected 29 hares, all of them European hares. Thermal binoculars accounted for 23 detections, or 79% of the total. Nineteen of these hares were sitting in daytime lays and four were moving. The remaining hares were detected visually or after they moved from cover. Overall, 55% of the hares were found in forested habitats, where ordinary visual detection would have been especially difficult.

Study figure showing hare survey areas and thermal imaging examples
Study sites and thermal-imaging examples from the Swedish survey. Figure 1 from Berndt et al. (2026), European Journal of Wildlife Research, CC BY 4.0.

Thermal binoculars accounted for most detections

The researchers could detect hares with the thermal binoculars at distances of up to 315 m in open terrain. Compared with surveys relying on ordinary visual detection, thermal imaging increased the number of hares observed resting in lays by about fivefold. In distance sampling, the decline in detections with increasing distance from a transect is used to estimate how many animals are likely to have been missed and thereby infer density. No hares were detected at the forest-dominated Grimsö site, so no density estimate was calculated there. At the two sites with detections, estimated density was 6.4 hares/km² at Lisjö and 8.1 hares/km² at the open agricultural Fiholm site. Uncertainty around both pilot-study density estimates was large.

Because this was a pilot study, the density estimates remain uncertain. The authors also note that walking surveys with thermal binoculars still depend partly on the observer’s decisions about where and how intensively to scan. They conclude that the approach is promising, particularly if future surveys cover larger areas and use greater sampling intensity. Locating daytime lays also creates opportunities to study lay characteristics and collect targeted environmental-DNA samples.

Sources and image credit

  1. Berndt, C., Kjellander, P., Spong, G., & Thulin, C.-G. (2026). Improved monitoring of hares (Lepus spp.) using thermal imaging combined with distance sampling. European Journal of Wildlife Research, 72(2), Article 49. https://doi.org/10.1007/s10344-026-02083-xPrimary peer-reviewed open-access study published 17 March 2026. At three sites in south-central Sweden, thermal binoculars detected 23 of 29 European hares and substantially increased daytime detection of hares resting in lays.

Image: Romzig / Wikimedia Commons — European hare photographed near Fågelfors, Sweden, on 3 May 2024; representative Swedish species image for the thermal-monitoring study, not one of the surveyed hares; cropped to 16:9 · CC0 · Source

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