Abstract
Aeshna caerulea (Azure Hawker) is present as a post-glacial relict in central European mountains. This species is listed as critically endangered in the Czech Republic (very restricted distribution occurring in two isolated populations) and the European population trend of this species is decreasing. The main objective of the study was to estimate the population size of A. caerulea in the Úpa bog National Nature Reserve (Czech Republic) using capture-mark-recapture data. Population estimates of adults using the Schnabel method was 425 (the 95% confidence limits: 248.1 / 992.3), and using the Schumacher-Eschmeyer method was 416 (the 95% confidence limits: 326.8 / 570.4). Imago activity became apparent at the beginning of July. This study has suggested that the possible future threats for the A. caerulea in the Czech Republic are drying up, air nitrogen depositions, eutrophication, pollution of water by external sources, and terrestrification, mainly as a result of global warming.