Canga, or ironstone, ecosystems are hotspots of old-growth plant diversity and highly specialized cave invertebrates. These ancient metalliferous habitats are amongst the most threatened ecosystems because of the destruction caused by large-scale iron ore mining. International debate on biodiversity offsets is increasing because these mechanisms are seen as tools for potentially balancing economic development with conservation biodiversity. Leading mining companies worldwide, including some of the largest iron ore producers in Brazil, are signatories to offset principles and best practices that aim to achieve no net loss of habitats, species or ecosystem functions. We aimed to analyse whether Brazilian legal requirements for biodiversity offsets result in the achievement of conservation outcomes or in elevated threat of extinction in canga ecosystems. We evaluated technical reports that support decision-making related to environmental licensing for iron ore mining and specific offset proposals linked to the Atlantic Forest Act. We found a relevant net loss in canga ecosystems and observed shortcomings related to the equivalency and transparency of offset principles. These deficiencies are mainly related to lax norms and regulations and the absence of an integrated database for accessing information on environmental licensing processes. We argue that both policy flaws and low engagement by the Brazilian mining industry in implementing offset principles have increased the threat of extinction in canga ecosystems.

Endemic insular species are particularly vulnerable to anthropogenic threats. The fish-eating bat Myotis vivesi is restricted mainly to the islands of the Gulf of California in Mexico and although several aspects of its biology have been studied there are no recent accounts of its current distribution. We conducted several expeditions during 2001–2016 to verify the current geographical distribution of this bat, and to record the presence of introduced predators. We identified the localities in which maternity colonies occur, estimated the size of the bat population on Partida Norte Island in 2003, and monitored bat presence on this island during 2004–2016. We found fish-eating bats on 36 islands and maternity colonies on 19 islands. Introduced rats Rattus rattus or cats Felis catus were captured on seven islands where the bats were present, and on five islands where they were absent. We estimated a population of c. 30,000 fish-eating bats in May 2003 and we confirmed the species’ presence on Partida Norte Island during 2004–2016. Based on the information compiled from our surveys and previous studies, we discuss the adequacy of the species’ current categorization as Vulnerable on the IUCN Red List, and its conservation status conferred by Mexican conservation authorities.