Analyse der Larvalhabitate des Braunen Eichen-Zipfelfalters Satyrium ilicis im Landkreis Heidenheim und mögliche Maßnahmen zu seinem Schutz

The Ilex Hairstreak (Satyrium ilicis) is listed as “critically endangered” in the German federal state of Baden-Württemberg. We investigated the small-scale distribution and habitat preferences of this species in one of its last areas of occurrence in Baden-Württemberg, the district of Heidenheim, in winter 2023/24. We surveyed a total of 1.986 young oak trees at 26 different study sites for S. ilicis eggs and confirmed the presence of the species at ten sites, grouped into four different clusters with distances > 1.2 km between clusters. We compared habitat patches and individual young oak trees where S. ilicis eggs were found with habitat patches and young oak trees without S. ilicis eggs. Our data show that the average height of oak trees in the habitat patches determines the selection of oviposition sites at the habitat patch level. Satyrium ilicis was most likely to occur in habitat patches with an average oak tree height of 2-3 m. At the level of individual host plants, S. ilicis preferred oaks in sheltered situations and oaks with small distances between the ground and the first branch. In addition to native oak species, we also observed eggs on planted Turkey oaks (Quercus cerris). From our results we derive characteristics of suitable larval habitats and provide recommendations for the conservation of S. ilicis in the study area. The recommended management measures aim to improve the spatio-temporal availability and connectivity of early successional habitats with young oak trees. In order to stabilise the critically endangered S. ilicis population, we recommend an early start of habitat management in the vicinity of currently occupied habitat patches.