Identifying hypotheses for drivers of decline of the bogong moth (Agrotis infusa)

Context Migratory populations of bogong moths in Australia are in decline. Numbers decreased after European settlement in the 1800s, and were stable before declining again from about 1980. Numerous hypothesised drivers for the decline have been postulated, and Caughley’s declining population paradigm provides a systematic approach to diagnosing which of these are important, and hence the knowledge to guide recovery actions. Aims This paper aims to assess which of the hypothesised drivers remain as candidate hypotheses for further investigation. Methods Within the context of known bogong moth life history and the timing of observed declines, hypothesised drivers of the two decline phases were assessed with respect to their potential impact on larval recruitment and adult survival during migration and aestivation. Key results Changes in vegetation composition and availability arising from the spread of pastoralism stand out as a likely driver of the early decline, with the herbivorous moth larva facing competition with introduced livestock, feral herbivores, and increased densities of native macropods. Many of the numerous postulated drivers of the most recent decline (e.g. changes in rainfall, rising temperatures in aestivation sites, increasing fire frequency) appear to have little support to be retained. Postulated drivers that remain as working hypotheses include increasing soil temperatures, increased cropping areas, and changed cropping practices and area. The effect of some drivers, such as artificial light pollution, is unclear and may warrant further investigation. Conclusions Inference on the drivers of bogong moth population decline is wanting. Implications Designed experiments are needed.