Current and Retrospective Numbers of Anseriform Birds in Autumn Migration in the Selenga River Delta (Republic of Buryatia, Lake Baikal)

After the results of autumn counts of waterfowl in the Selenga delta in 2018–2020, their recent numbers during the autumn migration are estimated and compared with the results of analogous intensive censuses in 1989–1995. A decrease in the numbers and percentages in some duck species is found (northern pintail, Eurasian wigeon, northern shoveler, and pochard); these parameters are rather stable in the mallard. Recent data on stopover longevity obtained in other regions of the world let us give more precise retrospective estimates for numbers of waterfowl having visited the Selenga delta during autumn migrations in the second half of the 1980s and the first half of the 1990s. More adequate numbers of stopping birds in the period mentioned above are 0.5–1.1 million individuals per season (at least, no less) instead of the 2–5 million proposed earlier. At present, the lower number limit for ducks having visited the delta per autumn season appears to be 0.3 million individuals; intensive counts during all autumn migration are necessary to set the upper limit. Numbers of waterfowl are approximately twice as low now as 30–35 years ago. The reasons for their decrease need to be sought outside the Selenga delta, probably in the general situation in regional and transregional geographical populations. The delta continues supporting more than 1% of the East Asian geographical population of the pochard, which has recently been labeled Vulnerable in the Red List of the IUCN. The Kabansky Nature Sanctuary plays a very important role as a no-take zone for waterbirds during autumn hunting seasons.