Mongolia's Gobi Desert ecosystem, a stronghold for populations of the Asiatic wild ass (khulan) Equus hemionus and the goitered gazelle Gazella subgutturosa, faces conservation challenges as a result of rapid economic development, including mining-related infrastructure projects. There is a paucity of reliable data on population abundance for these ungulates in the region, which makes it difficult to assess how they are responding to increasing anthropogenic pressure. Our aim was to obtain abundance estimates for khulan and goitered gazelles to inform their management and form the basis of a long-term monitoring programme. Each year during 2012–2015 we surveyed a total of 64 line transects spaced 20 km apart, with a total of 3,464 km of survey effort across 78,717 km2. Distance sampling analysis provided annual estimates of density and abundance, which were cross-referenced with the results of an aerial survey conducted in 2013. Overall, we observed 784 groups (14,608 individuals) of khulan and 1,033 groups (3,955 individuals) of goitered gazelles during the four surveys. The abundance estimates for 2013 were 35,899 (95% CI 22,680–40,537) khulan and 28,462 (95% CI 21,326–37,987) goitered gazelles. These estimates were congruent with the results from the aerial survey, which overlapped spatially and temporally with our ground-based survey. Our findings confirm that Mongolia's Gobi Desert supports the largest population of khulan and goitered gazelles in the world, and we provide a critical update on the status of the two species.

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