Ecological requirements and relative impact of threats affecting the Austral Rail Rallus antarcticus: Monitoring methodology considerations for an imperative conservation status re-evaluation

Abstract

Since its rediscovery in 1998, two major threats have been mentioned for the enigmatic Austral Rail Rallus antarcticus: cattle management by burning grass and rushes and predation by American mink Neovison vison. Added to the lack of a protocol to monitor this secretive bird, ever-growing threats make it necessary to study its global situation in depth to take accurate and urgent management decisions. We firstly studied how threats to the Austral Rail currently impact their occupancy and relative density (RD) at a wetland scale and habitat features associated with its presence at survey site scale inside wetlands in Santa Cruz province, Argentina. We additionally developed a monitoring protocol to detect the rail effectively and promptly by studying responses to playback with two different vocalisations at different times of the day and season. Both threats evaluated were negatively related to occupancy and RD of the Austral Rail, especially mink presence appearing to have an additive effect. We propose American mink control as crucial for Austral Rail conservation, while it would also be necessary to conserve a portion of wetlands exempt from burning and cattle presence. At survey sites, its presence was positively related with c.1-1.5 m tall rushes, whilst rails avoided low- density rush areas that resulted after management of rushes with fire to create pasture. To detect rails, both vocalisations can be confidently used at any time of the day and season. The poor knowledge about species ecology, mismanagement of vegetation in wetlands, expansion of American mink in Patagonia, construction on two dams in the Santa Cruz river basin, added to the already modified humidity conditions due to global climate change, force us to suggest that the Austral Rail should be considered as globally ´Endangered´ (EN), to ensure the consideration of the species in management decisions.