Declining breeding populations of White-naped Cranes in Eastern Mongolia, a ten-year update

SummaryEastern Mongolia supports one of the most important breeding populations of the White-naped Crane Antigone vipio (WNC), which is classified as ‘Vulnerable’ by the IUCN. Large numbers of WNCs were found to be breeding at high densities within the Ulz River basin during surveys conducted in 2000 and 2001, along a 270 km section of the river. Following these surveys, an extended drought continuing for at least a decade has threatened wetland ecosystems throughout Eastern Mongolia. This study reports the findings of surveys conducted in 2010 and 2011 along the same section of the Ulz River surveyed a decade earlier, as well as a generalised survey of other sites where breeding WNCs had previously been recorded. Along the Ulz River, populations declined from 42 territorial pairs in 2001 to 17 in 2011. Estimates of detection probability using distance sampling and occupancy methods at two locations gave consistent results of 23%–27% detectability. With a minimum population of 234 WNCs observed across all sites in 2011, these detection probabilities suggest that the areas surveyed support the majority of breeding WNCs in the western population. Although we cannot exclude the movement of WNCs beyond the survey area, these findings also suggest that the population has declined between 2001 and 2011. Exploration of key habitat variables using occupancy models and generalized linear mixed models found that WNCs favoured areas of high wet vegetation (estimated as ‘wet meadow’ coverage and using normalized difference vegetation index), and low grazing pressure. Given the importance of water resources to WNCs and nomadic herding communities, use of wetland habitat must be carefully managed to balance the needs of cranes and people, particularly during periods of drought.