THE TUNDRA SWAN, <i>CYGNUS COLUMBIANUS</i> (ANATIDAE), IN THE EASTERN ASIAN ARCTIC: TRENDS AND RANGES OF DIFFERENT FLYWAY POPULATIONS

Abstract

The tundra of the eastern Asian Arctic is inhabited by at least three flyway populations of the Tundra swan: the East Asian continental migratory flyway population of C. c. bewickii; the western Pacific flyway population of C. c. bewickii, and the western (American) flyway population of C. c. columbianus. The main objective of the present paper is to assess population trends by comparing information on the historical (the only one in the tundra of northeastern Asia) bird aerial survey in 1993–1995 with the data of our aerial survey held in 2020–2021. Another aim was to estimate the proportion of breeding birds in different flyway populations. The size of the zone of intergradation C. c. bewickii and C. c. columbianus in Chukotka and the level of hybridization have so far remained poorly studied, this issue required clarification. Aerial survey data for 2020–2021 were processed using 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 system made it possible to calculate the length of the survey. Estimates for each region were calculated for the extrapolation area given in the historical survey. Between 1993–1995 and 2020–2021, an increase in the numbers of all three flyway populations of the Tundra swan was revealed on the breeding grounds. The East Asian continental flyway population increased 3.86 times, vs. 3.05 times for the West Pacific flyway population (while the documented growth of this population was 2.1 times, according to mid-winter counts over the same period). The Western (American) flyway population grew 2.5 times. We believe that the northern border of the 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. 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. Kymyneyveem R (about 175.6° W) borders the areas of dominance of C. c. bewickii and C. c. columbianus. The switch in dominance has been triggered off, as there is no zone where both subspecies would occur in equal proportions. The overlap area of both subspecies extends for 600 km along the Arctic coast.