Absence of Evidence or Evidence of Absence? Concurrent Decline in the Host Plant Onobrychis alba and the Butterfly Polyommatus orphicus in a Montane Habitat of Northern Greece

Mount Falakro in Northern Greece historically hosted populations of the Balkan-endemic butterfly Polyommatus orphicus and its larval host plant Onobrychis alba. In this study, we surveyed six historically confirmed localities during the peak flight period of P. orphicus in 2024, but neither the butterfly nor the host plant were detected. While the historical data on both species are scarce and often imprecise, our field observations indicate severe habitat degradation, dominated by overgrazing and suspected climate-driven shifts. Habitat conditions were assessed qualitatively, with special attention to limestone substrates previously known to support O. alba. Although definitive absence cannot be statistically confirmed, the lack of detection in previously occupied sites raises urgent concerns about possible local extinction. Our findings suggest that both species may already be extirpated from parts of their former range. This case study underscores the conservation relevance of absence data and highlights the importance of site-based monitoring in mountainous ecosystems undergoing rapid environmental change. Long-term surveys, regulated grazing, and post-disturbance habitat restoration are urgently needed to clarify the conservation status of these species and guide future management strategies.