Studying Bird Migration

Researchers face a unique challenge when studying bird migration, as it is often difficult or impossible to follow birds as they migrate hundreds or thousands of miles between their breeding and wintering areas. It is also often impossible to identify individual birds among large flocks (have you ever tried to follow a duck or goose in a large flock on a lake or river near your home?). So, how do researchers study bird migration?

Banding Studies Scientists have developed several techniques to place bands on birds so that they can be easily identified. For small songbirds, such as warblers, researchers place small, metal bands on the birds’ legs. Each band is stamped with a unique number, so that when the bird is captured again or found, the researcher can look up the number to learn when and where the bird was first banded. This information can tell us a lot about a bird’s migration, as we can compare when and where a bird was banded with when and where it was resighted. Researchers in many countries are using similar techniques to band cranes. In the United States, for example, researchers from the International Crane Foundation are banding Sandhill Cranes to learn more about these birds in central Wisconsin. The researchers place brightly colored plastic bands on the birds’ legs, which are easily seen from a distance using binoculars. Each bird has a unique combination of colored bands and may also have a larger band with an engraved number. By looking up the color combination and number, the researchers can identify a banded Sandhill Crane in Wisconsin and compare past observations of the bird with their current observations. In east Asia, researchers are involved in similar studies with Siberian Cranes. Since 1990 nearly 70 Siberian Cranes have been captured and banded on their summering grounds in eastern Siberia (right). Many of these birds have been resighted along the east Asia flyway in China.

PTT Studies Although researchers have learned much about bird migration from banding cranes, it is still very difficult to follow cranes as they migrate, as a crane can fly hundreds of miles in a day during migration and may rest in remote areas that are difficult for people to access. As a result, scientists have developed ways to follow birds on migration using small transmitters (PTTs) that are attached to a plastic leg band or a harness (left) that is placed on the bird (similar to a backpack). The transmitters are designed to send signals to orbiting satellites, which in turn send data on the birds’ locations to researchers. Using these data, researchers can plot the birds’ migration on a map and can identify important areas that are used by the birds during their migration and at their wintering and summering areas. In 1995 and 1996 a team of Japanese and Russian researchers placed satellite transmitters on 13 Siberian Cranes on their breeding grounds in northeastern Russia. Five of the 13 birds were tracked approximately 3,000 miles to their wintering area in the Poyang Lake Basin in southeastern China. Through this study, researchers identified several important stop-over sites, including the Aumannykan area in eastern Russia, Qiqihar-Baicheng area in northeastern China and the Shuangtaizi River Delta and Yellow River Delta in eastern China. Prior to this study, researchers knew very little about the migration route and stop-over sites of the eastern Siberian Crane population.