The Roosevelt-Rondon expedition marmosetMico marcai: unveiling the conservation status of a Data Deficient species

The Roosevelt-Rondon Expedition marmosetMico marcaiwas first collected in 1914 and all information on this primate previously came from three skins brought back by this expedition. As a result,M. marcaiis categorized as Data Deficient on the IUCN Red List. As the presumed range ofM. marcailies on the path of the advancing arc of deforestation in Brazil, the collection of relevant data to assess the conservation status of this Amazonian species is of some urgency. Here we present the first field data on the distribution and population size of, and threats to,M. marcai, to reassess the species' conservation status. During 2012-2015 we surveyed the species in the Marmelos-Aripuana interfluve, and estimated its density using distance sampling. We also used spatial predictive modelling to estimate forest loss within the species range under two deforestation scenarios. We found the marmoset in 13 localities and estimated its extent of occurrence to be 31,073 km(2). We estimated the species' density to be 8.31 individuals/km(2)and extrapolated this to estimate a total population of 258,218 individuals (CI 150,705-441,860). Under a business-as-usual deforestation scenario, c. 10,000 km(2)of forest, comprising 33% of the species' range, would be lost in three marmoset generations (c. 18 years), and we, therefore, recommend thatM. marcaibe categorized as Vulnerable on the IUCN Red List based on criterion A3c. Other Amazonian marmosets require similar reassessment as their ranges also fall in the path of the arc of deforestation.