A call in the dark: Nocturnal flight calls and their potential to advance the study of avian migration

Abstract Migratory birds have experienced widespread declines in abundance and face numerous threats. The conservation of migratory species relies in part on improved knowledge of active migration behavior, but this behavior is difficult to study as most birds migrate at night. Flight calls, which are species-specific calls produced by many nocturnal migrants during flight, offer an opportunity to improve our understanding of migration behavior and serve as a tool to monitor populations. Although nocturnal flight call monitoring has been historically limited to small spatial and temporal scales, recent technological advancements have allowed researchers to largely shed these constraints. Despite this expansion, there are many unanswered questions regarding the function of flight calls and the proximate drivers of calling behavior. There are also unaddressed concerns that the methods used to record nocturnal flight calls, as well as other organismal, environmental, and social factors, may bias data in ways that impede (or prohibit) comparisons across time and space. Research that addresses these limitations and potential sources of bias will advance the use of nocturnal flight call monitoring for migratory bird research.