How do we study where migratory birds come from, where they go, and what routes they follow?
The most common method involves attaching leg or neck bands to birds, releasing them, and then when they're captured at a different location identifying where they came from by looking at the rings. However, this method requires the cooperation of many people, and also raises the problem of recapturing the birds.
In the 1990s, a method involving attaching tiny lightweight transmitters to migratory birds and tracking them using satellites became popular. The flight paths of migratory birds are called flyways. Satellite tracking has allowed scientists to learn more about hitherto uncertain aspects of the ecology and flyways of migratory birds.
Source: Hiroshi Kanai, Wild Bird Society of Japan
According to Noritaka Ichida of BirdLife Asia, "In the case of the Black-faced Spoonbill, for example, it was known that it spent the winter in Hong Kong, and that around 300 had been spotted in Taiwan, but we had no idea whatsoever where they bred. All sorts of research had been carried out in various countries, but it was still a complete mystery. But after studying the birds using satellite tracking, it was discovered that they in fact migrated to the demilitarized zone between South and North Korea (an area commonly referred to as the 38th Parallel), which surprised even experts."
The globe at left shows the distances the various species of shorebirds that inhabit the various regions of the world fly when they migrate. Looking at the results, you can see that they move over quite a distance, not in an east-west direction, but from north to south and vice versa. It was only recently that details of this movement of birds on a global scale became known. Knowledge of this movement allows scientists to carry out research into the spread of bird flu and other bird-borne viruses.
For a long time, the migration route of the Oriental Honey Buzzard, a species of hawk, was also a mystery. It was known that Oriental Honey Buzzards spent from spring to summer every year in Azumino in Nagano prefecture. A group led by Professor Hiroyoshi Higuchi of Tokyo University tracked these Oriental Honey Buzzards using satellites and discovered that after leaving Nagano in autumn, they flew from the Goto Islands north of Kyushu over the East China Sea to an area near the mouth of the Yangtze River, from where they flew south over mainland China and various countries in Southeast Asia, including Vietnam, Laos, Thailand, Myanmar, and Singapore, before finally arriving on the island of Java via the island of Sumatra in Indonesia. It was assumed that they followed the same route back to Nagano in spring, but it was found that they in fact followed a more westerly path up through Myanmar and continued north as far as the point where the Korean peninsula joins the mainland, from where they flew south to near Seoul and then across to Kyushu via the Tsushima Strait before returning to Nagano by heading across the Inland Sea in an easterly direction. The distance there and back is around 22,000 km, bearing in mind that they fly not in a straight line but along a circuitous route. According to Professor Higuchi, it is still unclear why the Oriental Honey Buzzards follow such a circuitous route, and why they fly different routes in the spring and autumn. Since satellite tracking began, great strides have been made in unraveling the mysteries of flyways, but at the same time new mysteries have emerged.
Source: Hiroshi Kanai, Wild Bird Society of Japan