The bogong moth migrates annually to the mountains of southeastern Australia in spring, to estivate at alpine altitudes, before returning to the plains in autumn to breed. Although occurring at low densities in the plains as larvae, when they estivate gregariously densities reach high levels, so that any chemicals carried by them are concentrated. One such chemical is arsenic, which is concentrated to phytotoxic levels in the soils surrounding estivation sites. Vegetation may recover as arsenic is made unavailable by time or by fire. This may be a cyclical process that has occurred many times in the past. Bogong moths are an important food for birds and small mammals, and arsenic has been found in the food chain, although bird deaths and population declines in small mammals cannot be positively ascribed to arsenic. Genetic studies and studies looking at the chemical form of the arsenic have so far been unable to confirm the source of the arsenic; however, interception of moths on their spring migration confirms that the source is away from the mountains.