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Eleven of 12 Tagged Whooper Swans Shared an Early Spring Migration Axis Before Routes Diverged

Whooper swan in flight
Research · Ecology

GNSS tracking of 12 whooper swans (Cygnus cygnus) wintering in the Nakdong Estuary in South Korea revealed a shared beginning to spring migration followed by markedly different routes and annual-cycle strategies. The study was first published online on 15 May 2026.

GNSS tags use satellite positioning to record where each bird is at repeated points through time, allowing researchers to reconstruct individual migration routes. Eleven of the 12 tagged swans initially followed the same broad west-central migration axis through Korea. In practical terms, almost all birds left the shared wintering area through the same geographical corridor before their routes diverged farther north.

Four broader migration patterns emerged after the shared start

The later movements fell into four patterns. Seven birds followed an inland route, one used a high-latitude strategy, two followed a Far East route and two showed short-distance or interrupted migration. The study therefore did not find one complete migration route shared by the Nakdong birds; it found a common early corridor followed by substantial individual variation.

Among six birds for which winter return could be assessed, three remained within a 20-kilometre return zone around the Nakdong Estuary. One bird re-entered this zone and later redistributed elsewhere, while two did not return to it. The 20-kilometre zone was used as a practical measure of return to the same wintering area rather than as proof that every bird reused the exact same sites within the estuary.

Spring journeys tended to use more stopovers

Four individuals produced interpretable round-trip tracks for both spring and autumn. Their spring migrations tended to be longer and to involve greater stopover use than the autumn journeys. A stopover is a temporary pause between longer migratory movements, when birds can rest and replenish energy before continuing.

With only four complete round trips, however, the seasonal differences were not statistically supported. The result is therefore a tendency in this small tracked sample rather than evidence that spring migration is generally longer or more stopover-intensive for the wider population.

Weather and vegetation relationships remained exploratory

Exploratory comparisons suggested that the timing and duration of stopovers may vary with freezing conditions before arrival and with seasonal vegetation development. The authors present these patterns as hypotheses generated from the tracks, not as firm causal explanations for why individual swans stopped where or when they did.

The strongest result is the combination of shared and divergent behaviour: almost all tagged birds used the same early northward axis through Korea, but later separated into very different migration strategies. This supports the Nakdong Estuary as both an important wintering area and a common early departure hub while showing that conservation of a single wintering population may need to account for several migration routes farther north.

Sources and image credit

  1. Paek, W.-K., Shin, Y.-H., Lee, S.-W., Kim, D.-H., Cho, H., Kang, J. H., Choe, Y.-J., Oh, H.-S., & Lee, J.-W. (2026). Shared initial migration axis and divergent annual-cycle strategies of whooper swans in the Nakdong Estuary, South Korea. Journal of Asia-Pacific Biodiversity. Advance online publication. https://doi.org/10.1016/j.japb.2026.04.005Primary open-access research article, available online 15 May 2026. GNSS tracking of 12 whooper swans tagged in the Nakdong Estuary found that 11 shared a west-central migration axis within Korea early in spring before later diverging into four annual-cycle strategy types.

Image: Ken Billington / Wikimedia Commons — whooper swan (Cygnus cygnus) in flight, photographed 9 February 2010; representative species image, cropped to 16:9 · CC BY-SA 3.0 — https://creativecommons.org/licenses/by-sa/3.0/ · Source

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