The great reed warbler undergoes marked long-term population fluctuations, and it is able to expand its range quickly when new habitat becomes available. This common and widespread bird is considered a species of least concern by the IUCN. Population size can be calculated with a suitability model, but direct counts of territorial males in suitable habitat and sampling the population sex-ratio can be a proper alternative to inference-rich predictive modeling based on imperfect habitat-extrapolation of densities of reed warblers at large spatial scales.