1. Why Tundra Swans and Whooper Swans in Japan Are Only Winter Visitors
In Japan, the swans you see are mainly two types: the Tundra Swan and the Whooper Swan. The Tundra Swan is slightly smaller, with a smaller yellow patch on its bill. The Whooper Swan is larger, and its yellow patch is bigger.[1]
These two species are winter birds that migrate to Japan. In summer, they are believed to be raising chicks in their northern breeding grounds. The Whooper Swan breeds in a wide area from Europe to Siberia, while the Tundra Swan breeds even further north, along the Arctic coast of Siberia.[2]
So, the swans you meet in Japan are only showing you the "winter part" of their annual life. The question remains: what route do they fly to reach their summer homes?
2. How Transmitters Show the Swans' Route Across the Sea of Okhotsk
The destination for summer has become clearer through tracking studies using transmitters. In a survey published by the Ministry of the Environment, the movements of Whooper Swans fitted with transmitters in Hokkaido were tracked by satellite.[3]
Swans that left their wintering grounds in early April to early May 2009 passed through Sakhalin and near the mouth of the Amur River. They crossed the Sea of Okhotsk and landed on the coast of eastern Russia. They arrived at breeding grounds in wetlands in the Kolyma River basin in late May to early June.[3]
This journey took about two months from departure to arrival. In autumn, they began migrating in early October and returned to the capture location between mid-October and mid-November.[3]
Another study tracking 47 Whooper Swans wintering in Japan from 2009 to 2012 reported that in autumn, they generally followed the same route as in spring, but in reverse. This study estimated their breeding grounds to be in the middle reaches of the Indigirka River and the lower reaches of the Kolyma River.[5]
However, this is based on records of tracked individuals. Not all swans move on the same schedule. Where do swans rest during this two-month journey?
3. Why Lake Kutcharo in Hokkaido Is a Spring Stop for Tundra Swans
Many Tundra Swans that come to Japan are said to pass through Lake Kutcharo in Hokkaido. This is a final spring stop for many Tundra Swans before starting their journey north.[6]
Lake Kutcharo is Japan’s northernmost Ramsar Convention wetland. The first swans arrive in early October in autumn, and they stay until around the end of Golden Week in May. The number of swans peaks in April because it is a relay point where they rest one last time in Japan before returning north.[6]
One Tundra Swan that wintered in Niigata Prefecture and was tracked by the Ministry of the Environment followed a similar route. It left its wintering ground in mid-to-late March, moved to Hokkaido, crossed the Sea of Okhotsk via Sakhalin, and landed in eastern Russia in mid-May. It arrived at wetlands in northeastern Russia in early June, started its autumn migration in late September, and returned to the capture site in late October.[4]
This is just one example, not an average for all Tundra Swans. Once they arrive in Honshu, how do swans spend their winter days?
4. How Swans Near Lake Mikata Sleep in the Lake and Eat in Rice Fields
In a survey around Lake Mikata in Fukui Prefecture, swans were found to roost in the lake. In the morning, they fly from the lake surface to rice paddies, where they eat and rest, before returning to the lake in the evening. This is a commuting lifestyle: night in the lake, day in the paddies.[7]
Their food includes fallen rice ears, leaves, stems, and roots of grass, aquatic plants, and algae. Sometimes they also eat small invertebrates.[1]
When eating plants underwater, encyclopedias explain that they put their long necks into the water or stand upside down in deeper areas.[2]
The rice paddies studied had specific features. They were not plowed and had partially accumulated water. Swans dug at the base of rice stubble with their bills or ate second-growth rice ears. Rice paddies after harvest seem to be open spaces where food is placed for swans.[7]
But in winter, lakes in Hokkaido freeze. When they freeze, where do swans spend the winter?
5. Why Whooper Swans Gather at Unfrozen Hot Spring Waters in Hokkaido
On the shore of Lake Kusharo in Hokkaido, there are several spots that do not freeze even in midwinter due to the heat from hot springs. Around the waters of Kotan Onsen and Sunayu Onsen, Whooper Swans from Siberia can be seen gathering.[8]
Unfrozen waters seem to be one of the important places for swan life. Winters in Hokkaido are cold enough that many lakes freeze, and the two species spend winter differently. Tundra Swans winter in lakes and wide rivers in Honshu, with some individuals migrating as far as western Japan. Few Tundra Swans winter in Hokkaido; they are often seen as migratory birds passing through in autumn and spring.[9]
On the other hand, the wintering grounds for Whooper Swans are biased toward northern Honshu and northward.[7]
The records show three parts of their annual cycle: raising chicks in Russian wetlands in summer, resting in relay points like Hokkaido in spring and autumn, and living in lakes at night and rice fields by day in winter.
6. How to Trace the Swans' Route on a Map from Hokkaido to Russia
Open an atlas and look for Hokkaido, Sakhalin, and the Sea of Okhotsk. Trace the route with your finger, starting from Hokkaido, passing by Sakhalin, crossing the Sea of Okhotsk, and reaching the coast of eastern Russia. Tracing the route on a map allows you to check the distance from Hokkaido to eastern Russia.
The Ministry of the Environment website has a page showing the migration routes of swans fitted with transmitters. Comparing how much the spring and autumn routes overlap makes the journey more concrete.
Local government websites also provide information about places where swans arrive. Checking if there is a landing site in your area, and where they are at night versus during the day, could be the next question to explore.