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|NatureInterface > No.06 > P015-017||[Japanese]|
The Journey of Migratory Birds:
Where Do They Come From and Where Do They Go?
Keeping Track of Migratory Birds Through the Use of Satellites
The Earth we are living is blessed with beautiful nature in which a great variety of wonderful lives exist. Nowadays, it is becoming increasingly significant to explore how nature and life exist and related. Basic research constitutes one aspect of this interest, and the other research is to conserve the natural environment and wildlife. Both of these researches require a wide range of in-depth surveys.
As far as migratory birds are concerned, however, our conventional methods can barely keep track of them because they virtually migrate across the globe.
As I mentioned at the outset, our Earth is blessed with beautiful nature and wonderful life. Take demoiselle cranes as an example; they migrate the peaks of the Himalayas, which rise 7,000-8,000 meters above the sea. The spectacle of tens of thousands of these cranes flying against the background of the snow-white surface of the mountains is truly magnificent. However, their migration pattern such as where and how they come from and go still remains in the realm of a great mystery.
In the same manner as stated above, more than 10,000 cranes migrate to Izumi City in Kagoshima prefecture every year. We know that they come from somewhere in the Asian Continent, but their migration routes have been a big mystery. We, bird researchers, have used such generally used method as leg bands or collars, in an effort to unravel these mysteries. First, we mark each bird using a colored band with an identification number. Then, we either recapture or observe these birds; their migration routes are traced according to their identification numbers.
There is great significance in this kind of survey which provides us with very important information. But quite unfortunately, as far as migration is concerned this method requires a lot of time and effort, only to get the fragmented information. With this problem as a backdrop, and in response to the needs for a series of basic and applied researches and for the purpose of collecting a massive amount of precise data quite efficiently, a tracking method using a satellite has recently been developed.
The whole system is abbreviated as °»satellite tracking.°… NOAA, a satellite we are now using for our survey, orbits the Earth once every 100 minutes or so. This is how the system works; the transmitters attached to birds send signals to the satellite, which in turn sends those signals back to ground stations; the world information processing centers in Alaska, France and other locations analyze the relayed signals to convert into data indicating latitudes and longitudes; and those data are sent to our computers through the Internet. Once transmitters have been attached to birds, computers do the rest of the work ? a great laborsaving process.
Transmitters vary in configuration and function, but they are about the same size as a matchbox. Each transmitter has its own number, so that it can be identified. They are attached to birds with Teflon-coated ribbons, both ends of which are fastened by hooks that will corrode and drop within a certain period of time at fastest, thereby releasing the birds from the transmitters. The data we actually receive are just a series of figures, but they can be available within a minute or two after the original signals have been sent out from the transmitters. In other words, we can keep track of any animal ? of course even human beings ? that migrates on the Earth in real time. It is indeed an epoch-making system.
A massive amount of figures are fed into computers, so we need to analyze and plot them on a diagram. This work is done by software called °»Elsa,°… which can indicate the location of each bird on the individual bases. It is also possible to calculate the distance between given locations by enlarging this information.
Japanese Cranes Migrate to DMZ Over the Himalayans
Black Cranes Migrate to Russia Through Afghanistan
So what have we found out? A survey on white-naped cranes has been the first successful case. They leave Izumi and head northward in the direction of the Korean Peninsula (please see Fig. 10), occasionally stay overnight in Tsushima or somewhere in the Goto Islands, and then stay for a while in the DMZ on the Korean Peninsula before dividing into two groups heading for different destinations: one group travels northward along the east coast of the Korean Peninsula and heads for Lake Khanka that is located on the Chinese-Russian border, or ground on the Sanjiang Plain in the Heilungkian Province that is surrounded by the Amur, Songhua, and the Ussuri, and breed there; and the other group heads for an area called Zaron, which is close to Qiqihar of the Heilungkian Province.
By contrast, big, beautiful and graceful Japanese cranes do not migrate to distant places. In Japan, they breed and overwinter in Hokkaido. But some other groups of cranes breeding on the Continent travel several thousand kilometers to overwinter in the southeast region of China or on the Korean Peninsula. By keeping track of a group that had left for flight from the middle reaches of the Amur, we found out that they divided into two groups: one migrated to Yangheng, located north of Yangzi Jiang by way of the Bohai coast and the mouth of Huang He; and the other group migrated to the DMZon the Korean Peninsula likewise, traveling southward along the Korean Peninsula.
A study group led by the Wild Bird Society of Japan, taking the lead in surveying on demoiselle cranes flying over the Himalayans, which I mentioned earlier, found out the exact migration route of these cranes; they migrate from Russia, Mongolia, and Kazakhstan all the way to India, by way of the Himalayas.
In addition, we recently succeeded in keeping track of a migration route of storks from their starting point of middle reaches of the Amur. First, we looked for nests of storks from a helicopter. Finding a grown young bird in a nest, we descended nearby to attach a transmitter to it. We marked ten-odd birds in total. It turned out that they first headed for the mouth of Huang He, following a route similar to that of Japanese cranes. But unlike Japanese cranes, they subsequently migrated to Poyang Lake, which is located in the middle reaches of Yangzi Jiang.
Meanwhile, technology is making rapid progress. For example, the life expectancy of batteries, which was only about three months long at first, has improved dramatically, as the design of transmitters and the quality of batteries make great strides. Therefore, it became possible to keep track of the entire migration routes of the individual subjects: southbound routes in fall and northbound routes in spring. As a result, it turned out that they did not return to the places where they were born. All of them fly to the different places from where they left; the stork born in some place descends southward and flies in opposite way in sprig. They never return to where they were. That is, they migrated to different places and spent the following summer there.
We also found out that black cranes migrated all the way to the southern part of Russia by way of politically unstable countries such as Pakistan and Afghanistan, and bred there.
By keeping track of these cranes using a diagram on a display, I can easily imagine them flying in beautiful formation.
There are, of course, neither Boundaries nor Passports for Migratory Birds
In addition to migration routes and periods, satellite tracking provides us with a lot of valuable information such as behavioral patterns in the passage of migrations (please see Fig. 02). For example, we were able to track down how long cranes usually stay at transit areas on their way to their respective destinations. These transit areas are Panmunjom, Cheolwon, both of which is in the DMZ on the Korean Peninsula, Kumya, located on the east coast of North Korea, and Khanka, located on the Chinese-Russian border.
One of the birds we surveyed took a total of 28 days to migrate, about 75% of which were spent in Cheolwon. As we carried out the survey this way, we found out that bird No. 1 to No. 5, for example, spent about 60% of their migration periods either in Panmunjom or Cheolwon.
We often say that there are no boundaries for migratory birds. Indeed, boundaries are politically determined by human beings, and hence have no biological significance. As you know, cranes migrate from one country to another without passports or visas. Boundaries have no biological significance at all. But ironically, the DMZ on the Korean Peninsula has become a sanctuary for migratory birds, as the area is off-limits and protected from any economic activity, while other parts on the peninsula, like most other places in the world, are being exploited. I think this is a very important message the results of our survey bring to us.
From the Behavioral Tracking of Migratory Birds to Environmental Conservation
During these activities, we can also keep track of the distance between a mother crane and her young one as they migrate together by attaching transmitters to both of them. In other words, we can identify the location in which they part from each other by keeping track of the distance between them. In the case of white-naped cranes heading northward from Izumi, for example, mother cranes and their young ones are relatively close to each other until mid-March. But the distance between them becomes great suddenly upon arriving in the Heilungkian Province, their breeding area. This fact indicates that they part from each other in the Heilungkian Province. Their behavioral patterns can be traced in this manner.
In order to conserve the natural habitats of endangered species like cranes and stalks, it is important to know the kinds of places they use, transit areas they take, and the migration routes that is environmentally satisfied for them they take. And these can be analyzed by plotting the results of tracking through satellite imagery, which plays an important part in environmental assessment.
Stalks usually take a route along the basin of the Amur. In other words, wetlands along great rivers are indispensable for them.
But once they enter China, the situation changes dramatically. Natural wetlands are very scarce in China, and hence he stalks have no choice but migrate over grassy plains and cropland; they are forced into a difficult situation.
All the surveys I mentioned above were carried out with the help of the information retrieval and survey system called the ARGOS system aboard NOAA, a weather satellite. This system can measure the positions of subjects and collect relevant information based on the radio waves emitted by those subjects. However, we are beginning to use GPS (Global Positioning System), which is becoming widespread for use in car navigation and other positioning systems. GPS is a system where a satellite itself emits radio waves through which subjects determine their positions. Professor Fukuda introduces the use of GPS for keeping track of migration routes in the latter half of this special feature article.
As for future plans, we are going to clarify environmental capabilities based on a variety of combinations between satellite imagery and satellite tracking. How are migration routes determined? Or how do they change, or how can they be changed if certain key locations in the routes are lost? These are the things we want to study.
Needless to say, we are not doing satellite tracking just for entertainment. Our research is intended for protecting targeted species and conserving their natural habitats. It has been only about ten years since the research started, but there have been some fruits of the results of satellite tracking and its relevant information: several natural parks, as well as national nature reserves in two regions in North Korea were established; and a conservation plan is being prepared for the Sanjian Plain in China making good use of the results of our survey. Applying in various forms, some significant messages are emerging that otherwise would go unrevealed.
Naturally, this kind of extensive research cannot be handled by a single researcher, and hence we are conducting it in collaboration with various institutes, countries and regions. Exploring collaboration with researches in various fields, we are committed to making full use of our findings in order to be proved to be helpful in conserving wildlife.
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