Thirteen Years of Counting Migration in Batumi: Observations and Their Importance for Raptor Conservation in Russia

One of the most important autumn migration bottlenecks for birds of prey in the Western Palearctic is situated in South-Western Georgia, between the east coast of the Black Sea and the range of Lesser Caucasus. Every year from mid-August till October at least 1% of the world’s population of 10 raptor species passes through this corridor. Specifically, over one million raptors are recorded annually, including on average 528467 Honey Buzzards (Pernis apivorus), on average 163985 Black Kites (Milvus migrans), 304819 Steppe Buzzards (Buteo buteo vulpinus), and around 8000 Lesser Spotted Eagles (Aquila [Clanga] pomarina). The specifics of the landscape and relief makes the foothills of the Lesser Caucasus to the north of Batumi an ideal spot for counting raptor migration, and since 2008, an international team of volunteers, the Batumi Raptor Count, has monitored autumn raptor migration from two strategic vantage points. The count effort is focused on 7 priority species, including Honey Buzzard, Black Kite, Lesser Spotted Eagle, Booted Eagle (Hieraaetus pennatus), Marsh, Montagu’s and Pallid Harriers (Circus aeruginosus, C. pygargus, C. macrourus, respectively). In addition, 13 other diurnal raptor species and 10 non-raptor bird species are monitored at the BRC. Using the trektellen-app, BRC is able to record all data digitally in the field, and to provide daily updates of migration counts on its website. At the end of each season, the data is cleaned and made available through the Global Biodiversity Information Facility (GBIF). Protocols were developed to standardize count effort across years, thus allowing an accurate assessment of population trends in the priority species. Importantly, the BRC systematically records data on the age and sex of raptors, allowing to infer trends separately for different demographic groups. The standardized data collected from 2011 till 2019 revealed rather stable numbers for most priority species, but also a significant annual decrease in numbers of juvenile Montagu’s Harriers; a strong ongoing increase in numbers of both juvenile and adult Black Kites; and increase in numbers of adult Booted Eagles accompanied by a decrease in juvenile birds of this species. Based on GPS-tracking studies on a variety of species, it appears that the western border of the breeding area for the populations counted by BRC is most probably not too far away from the western border of Russia. At least in case of Spotted Eagles, individuals breeding in the Baltic States, Finland, and Germany tend to use the migration routes to the West from the Black Sea, and this is also the case for birds from Western Ukraine and Belarus. There is insufficient data available to define the eastern border for the populations migrating through Batumi. We do know that raptors tracked from the south of Siberia tend to migrate to the east from the Caspian Sea, although some Pallid Harriers tracked from Russia and Kazakhstan do migrate over the Caucasus. All considered, we assume that the vast majority of raptors observed in Batumi during autumn migration breed in Central European Russia up to the Ural Mountains. A comparison of Batumi counts with the breeding population size estimates in Russia and neighbouring countries suggests that a significant proportion of the Russian population of the Lesser Spotted Eagle and Honey Buzzard is passing through the Batumi bottleneck on migration. Trends in migration counts at Batumi are probably representative of changes in raptor breeding populations from European Russia and Western Kazakhstan. In addition to collecting the data on migration, the BRC supports the development of ecotourism in the area and combats the widespread poaching of migrating raptors in Georgia by implementing various educational programs in schools and higher education institutions in Georgia. The BRC would like to build stronger links with professional ornithologists and amateur birdwatchers from the breeding areas of the raptors that pass through Batumi each year, and cordially invites everyone to participate in its migration counts.