No Effect of a Commercially Used Odor Repellent for Roe Deer (Capreolus capreolus) Protection During Meadow Harvest.

In Central Europe, the fawning season of roe deer (Capreolus capreolus) directly overlaps with meadow and alfalfa harvest, typically from late May to early June. During these operations, tens or more likely hundreds of thousands of fawns are mutilated by agricultural machinery. To mitigate this unethical mortality, wildlife managers often deploy odor repellents to drive roe deer individuals from high-risk fields before mowing. Therefore, we evaluated repellent efficacy in a paired design. The abundance of roe deer was quantified by drones equipped with thermal cameras before and after repellent application and then compared with untreated control meadows. Results showed high adult abundance that did not differ significantly among treatments. The highest median was paradoxically observed on meadows "after application" (8.25 ind./10 ha), followed by "not treated" meadows (7.92 ind./10 ha), and "before application" (5.72 ind./10 ha). For fawns, differences between treated and untreated plots were likewise non-significant. Their numbers increased over time after application, consistent with the peak of parturition in the second half of May. Overall, the study confirms that the tested odor repellent, when applied according to the manufacturer's protocol, did not reduce roe deer presence on meadows. This underscores the need to consider alternative approaches, such as the use of thermal-imaging drones combined with the subsequent translocation of detected fawns to safe locations.