Aestivation as a response to climate change: the Great Banded Grayling Brintesia circe in Central Europe

1. Climate change has forced species to shift distribution, alter migration behaviour, or change phenology. One of these adaptation strategies is aestivation to overcome hot, dry summers. For example, the abundance of the Great Banded Grayling Brintesia circe Fabricius (Lepidoptera, Nymphalidae) in Southern Germany used to show one flight peak between June and August, while now, a bimodal phenological record suggests 3–4 weeks of aestivation during the driest summer weeks. 2. To study this new phenomenon, a capture‐mark‐recapture study was performed in two nature reserves in Southern Germany during 92 days in 2019 and 2020. Gender, wing condition, and exact location of individuals of B. circe were recorded. These data show that in June (first flight period), 76%, 481 of 635 captured individuals were males, while in late August and September (second flight period), ≥95%, 452 of 462 were females. No individual marked during the first flight period was recaptured during the second flight period. 3. The results imply that mating takes place during the first flight period only, especially females aestivate, probably to avoid oviposition during the hottest and driest parts of the summer and that an unknown part of the population may disperse out or into the investigated habitats. This behaviour appears to have changed during the last decades probably as an adaptation to climate change. Females of B. circe are forced to oviposit later in summer as earlier eggs laid during hotter and drier times are less likely to develop successfully. Our study found a shift in the phenology of Brintesia circe over the last decades. While there used to be one peak, now there are two peaks separated by a time of reduced, or even no, flight activity. During the first flight period, we caught more males than females, while during the second flight period we caught almost exclusively female.