Tracking swans in the East Asian flyway

By Lei Cao, Anthony D. Fox & Eileen C. Rees

The migration routes and main sites used by migratory waterbirds have been studied in Europe and North America since the mid-20^th century, leading to the identification of discrete populations which form the basis for internationally coordinated conservation and management of these species. Until recently, however, there was a lack of comparable information about migratory Anatidae populations in Far East Asia, despite long-term monitoring programmes and some knowledge of migration routes based on Japanese satellite tracking (Cao et al. 2020). Tracking of 10 large-bodied Anatidae therefore was undertaken as a collaborative programme involving inter alia Chinese, Japanese, Korean, Mongolian and Russian researchers from 2014 onwards, and the results published in a Special Issue of the Wildfowl journal in November 2020. The papers combined the new telemetry data with winter counts and expert knowledge, to update maps of the extent of breeding and wintering areas, and to define the flyways that connect them. Critical stopover sites were also described, to provide a basis for their more effective future conservation.

Whooper catching in Mongolia by Otgonbayar Tsend WSCC of Mongolia

Whooper catching in Mongolia, (c) Otgonbayar Tsend/WSCC of Mongolia.

Three swan species native to East Asia – Whooper Swans Cygnus cygnus, Bewick’s Swan C. columbianus bewickii and Mute Swan C. olor – were all included in the study, and the results provided valuable novel information on their distribution and movements. Bewick’s Swan tracking data described two distinctive flyways for birds in the East Asia population: (1) the East Asian continental flyway, with birds breeding from Yamal Peninsula to the Svyatoy Nos Cape wintering in China, and (2) the West Pacific flyway, taken by swans which swans bred between the Indigirka River and Chaun Delta, which wintered in Japan (Fig. 1, from Fang et al. 2020). There was marked between-year variation in population-level Bewick’s Swan count data recorded during the 21^st century, reflecting incomplete coverage in some years. Numbers in the East Asia population were however most recently put at c. 65,000 birds following extensive wintering survey coverage in 2019–2020, compared to c. 81,000 in the early 2000s when coverage was less extensive, indicative of a population decline during the past two decades (Fang et al. 2020).

Figure 1. Migration routes for Bewick’s Swan tracked along the East Asian continental flyway (black dashed line), and (2) the West Pacific flyway (red dashed line) in East Asia (from Fang et al. 2020).

Whooper Swan tracking focussed on birds which spend the summer in western Mongolia and results indicated that the swans’ summer distribution extended further than had previously been recorded, with three new wintering areas (in Xinjiang, Qinghai-Gansu and Beijing) identified for the species in China (Ao et al. 2020). The East Asian Whooper Swan population was estimated to number 57,690 individuals, generating a new 1% threshold of 577 birds for determining sites of international importance for the species in the region, with eight located in China, six in South Korea and 14 in Japan. Migration duration, stopover duration, the number of stopover sites and migration legs were significantly greater in spring than in autumn, whilst migration speed was slower in spring than in autumn. Assessment of the habitats frequented found seasonal variation in the proportion of time that the swans spent on arable crops, pasture, wetlands and open water (Ao et al. 2020).

Figure 2. Migrations recorded for individual Whooper Swans in East Asia: (A) birds summered in Mongolia and wintered in China/South Korea; (B) birds summered in Far East Russia and wintered in Japan (from Ao et al. 2020). White solid lines = individuals from the Chinese-wintering population; black solid lines = individuals from the South Korean-wintering population, all of which summered in Mongolia (Ao et al. 2020). Orange dotted lines = representative (synthesised) migration routes, and orange shaded areas = representative summering/stopover/wintering areas for 47 tracked birds that summered in Russia and wintered in Japan (from Shimada et al. 2014).

The Mute Swan study was less comprehensive, but telemetry data and resightings of birds fitted with neck-collars confirmed that the species winters along the coast of eastern China and on the Korean Peninsula, and spends the summer along the Selenga River (Russia), central Mongolia and in Inner Mongolia (China). It is widespread but relatively scarce and scattered in East Asia, and although Mute Swans wintering in Korean Peninsula apparently originate from summering areas in Inner Mongolia and the Amur Region, further study is required before potential flyways can be confirmed (Meng et al. 2020). The sedentary introduced Mute Swan population in Japan does however appear to be isolated from those elsewhere.

Further information on these studies, and also on other species included in this initiative, are available online through the journal’s website at Wildfowl (wwt.org.uk).

References

Ao, P., Wang, X., Meng, F., Batbayar, N., Moriguchi, S., Shimada, T., Koyama, K., Park, J.-Y., Kim, H., Ma, M., Sun, Y., Wu, J., Zhao, Y., Wang, W., Zhang, L., Wang, X., Natsagdorj, T., Davaasuren, B., Damba, I., Rees, E.C., Cao, L. & Fox, A.D. 2020a. Migration routes and conservation status of the Whooper Swan Cygnus cygnus in East Asia. Wildfowl (Special Issue No. 6): 43–72.

Cao, L., Deng, X., Meng, F. & Fox, A.D. 2020. Defining flyways, discerning population trends and assessing conservation challenges of key Far East Asian Anatidae species: an introduction Wildfowl (Special Issue No. 6): 1–12.

Fang, L., Zhang, J., Zhao, Q., Solovyeva, D., Vangeluwe, D., Rozenfeld, S.B., Lameris, T., Xu, Z., Bysykatova, I., Batbayar, N., KoNishi, K., Moon, O.-K., He, B., Koyama, K., Moriguchi, S., Shimada, T., Park, J.-Y., Kim, H., Liu, G., Hu, B., Gao, Ruan, L., D., Natsagdorj, T., Davaasuren, B., Antonov, A., Mylnikova, A., Stepanov, A., Kirtaev, G., Zamyatin, D., Kazantzidis, S., Sekijima, T., Damba, I., Lee, H., Zhang, B., Xie, Y., Rees, E.C., Cao, L. & Fox, A.D. 2020. Two distinctive flyways with different population trends of Bewick’s Swan Cygnus columbianus bewickii in East Asia. Wildfowl (Special Issue No. 6): 13–42.

Meng, F., Chen, L. Fang, L., Zhang, B., Li, C., Zhao, G., Batbayar, N., Natsagorj, T., Damba, I., Liu, S., Woods, K., Cao, L. & Fox, A.D. 2020. The migratory Mute Swan Cygnus olor population in East Asia. Wildfowl (Special Issue No. 6): 73–96.

Shimada, T., Yamaguchi, N.M., Hijikata, N., Hiraoka, E., Hupp, J.W., Flint, P.L., Tokita, K.-i., Fujita, G., Uchida, K. & Sato, F. 2014. Satellite tracking of migrating Whooper Swans Cygnus cygnus wintering in Japan. Ornithological Science 13: 67–75.