Tundra swan Cygnus columbianus (Anatidae) in the eastern Asian Arctic: trends and ranges of different Flyway Populations

By D.V. Solovyeva, D.A. Barykina, G.V. Kirtaev, V.V. Nikiforova and S.B. Rozenfeld

The tundra of the eastern Asian Arctic is inhabited by at least three Flyway populations of the Tundra swan: East-Asian continental migratory Flyway population of C. c. bewickii; Western Pacific Flyway population of C. c. bewickii and Western (American) Flyway population of C. c. columbianus.

The goal of the paper is to assess population trends by comparing the data of the historical (the only one in the tundra of North-East Asia) aerial survey in 1993-1995 with the data of our aerial survey in 2020-2021. Additionally, we aimed to estimate the proportion of breeding birds in different Flyway populations. Size of the zone of intergradation C. c. bewickii and C. c. columbianus in Chukotka and the level of hybridization have remained poorly studied so far; clarification of this issue was one of the goals of this work.

C. c. columbianus by Nick Cottrell / WWT

Aerial survey data for 2020-21 were processed with in QantumGIS 9.16.5 software. The system included the following layers: a vector layer of the world map; routes of aerial surveys for 2020 and 2021; and polygons of counts for 1993-1995. The population estimates were calculated for the overall expanded areas given in the historical survey.

Linear densities (individuals/km in the 400 m survey strip) and estimates (individuals) of the Tundra swan populations in 1993–1995 and 2020–2021.

Between 1993-95 and 2020-21 an increase in the number of all three Flyway Populations of the Tundra swan was revealed in the breeding grounds. The East-Asian continental Flyway population increased by 3.86 times; the West Pacific Flyway population by 3.05 times (while the documented growth of this population according to Mid-winter counts over the same period is 2.1 times). The Western (American) Flyway population grew by 2.5 times. We believe that the northern border of summer range of the Tundra swan has significantly shifted to the north, following the summer climate change and the northward shift of the subarctic tundra zone. The registration of nests and broods in areas where only non-breeding birds were recorded during the historical survey is additional evidence of a northward displacement of the range. Overall, the East Asian continental Flyway population is likely to number 75-80,000 swans and is likely to experience a positive trend in the 21st century, similar to other Flyway populations of the species. The West Pacific Flyway population was estimated at 41,928 swans in 2020-2021, which is 78% of the winter number in January of the same years, regardless the proportion of offspring and annual mortality.

The full article can be found here