Hermit beetle ( <i>Osmoderma barnabita</i> ) habitat selection and movement are shaped by tree microhabitat availability in Eastern Romanian Carpathians

Abstract Loss of old‐growth and mature forests threatens the long‐term persistence of saproxylic beetles, keystone species essential for ecosystem functioning. Effective conservation requires detailed knowledge of their habitat requirements and dispersal capacity, which remain poorly understood in Eastern Romanian Carpathians. In this study, we used radio‐telemetry to examine the movement ecology and habitat selection of Osmoderma barnabita in a closed‐canopy mature mixed broadleaved forest with scattered veteran trees, interspersed with hay meadow clearings (hereinafter mature mixed broadleaved forest) of the Eastern Romanian Carpathians, an area where the species' distribution and ecology have been largely underreported in the literature. Our VHF telemetry‐informed study of Osmoderma barnabita found that female beetles recorded the longest movement distance (401 m) and had larger home ranges than males, while their core home ranges were similar. We found that Osmoderma barnabita showed a clear preference for Quercus petraea , with its presence best predicted by wood mould cavities, tree height and diameter. Additionally, selection for shaded microhabitats and limited movement suggests that the populations show distinct ecological responses, likely adapting to the drier, warmer summer conditions of the Eastern Romanian Carpathians. Our results provide insights into microhabitat and stand types suitable for Osmoderma barnabita in the Eastern Romanian Carpathians and emphasize the importance of larger trees with microhabitats that take a long time to develop (cavities with suitable substrates for oviposition). This may reflect local adaptation, responses to environmental conditions or early signs of climate‐related range shifts.