Estimating the autumn staging abundance of migratory goose species in northern Kazakhstan

Abstract

Northern Kazakhstan and adjoining areas of Russia have vitally important autumn staging sites for arctic breeding geese, especially for the globally threatened Lesser White-fronted Goose Anser erythropus (LWfG) and Red-breasted Goose Branta ruficollis (RbG). Part of the Fennoscandian and the entire Western Main subpopulations of LWfG and the global population of RbGs are believed to stage there, which facilitates obtaining up-to-date population estimates for these species. A total of 80 lakes were surveyed across four survey areas in autumn 2016, recording more than 1.2 million geese in the region. Greater White-fronted Geese Anser albifrons (GWfG) were the most abundant with an estimated c. 890,000 birds, with counts of c. 250,000 Greylag Geese Anser anser, c. 53,000 Ruddy Shelduck Tadorna ferruginea, c. 39,100 RbG and c. 32,000 LWfG also recorded during the surveys. Based on a priori lake classification for both LWfG and RbG, to stratify survey lakes in order to generate total population estimates, survey teams visited a sample of different lake types. After removing lakes smaller than the observed minimum lake size used by each species, the total number of potential lakes available within the core staging areas of each species (335 lakes of > 320 ha for LWfG; 361 lakes of > 100 ha for RbG) was calculated. Bootstrapping procedures, with replacement, were then used to estimate the total numbers likely to be present in the region. These calculations produced total estimates of 34,250 birds (95% confidence intervals = 28,500–40,100 birds) for the Western Main population of LWfG (well in excess of current population estimates of 8,000–13,000 individuals) and an estimated population of 50,100 RbG (95% CI = 28,100–72,600 birds), broadly similar to recent population estimates of 55,000–57,000. We recommend that future surveys continue to monitor as large a region and as many lakes as possible in order to capture inter-annual variation in the distribution of birds and to provide more reliable assessments of population size and trends of these migratory species.