In order to identify and keep track of individual birds, scientists put aluminum or colored bands on birds' legs. Similar to the license plate on a car, each aluminum band is engraved with a unique set of numbers.
Bird banding is one of the oldest and most important techniques used for studying and identifying individual birds. In the early 1800s, John James Audubon tied threads to birds' legs to identify individuals that were visiting his farm. In 1902, the first scientific study to use bird banding took place in the United States: Smithsonian scientists attached bands to the legs of black-crowned night herons at the Smithsonian's National Zoo in Washington, D.C.
How do researchers band birds?
In many countries, bird banding is regulated by the federal government. In the U.S., the Bird Banding Laboratory (BBL), part of the United States Geological Survey, provides scientists with aluminum bands and keeps records on all banded birds. Scientists must submit an application to receive bands from the BBL. They are required to show proof of their skill in safely handling birds, explain why they need to band birds as part of their research and provide information on where the research will take place. Each bird that is given a tracking device, such as a light-level geolocator or satellite transmitter must also be banded.
Before a bird can be banded, it must be caught. For smaller birds, researchers use mist nets—tall, long nets made of very fine threads that blend into the surroundings. Mist nets are stretched between two poles that are usually placed in the ground, but can also be placed in the canopies of trees. Birds caught in the nets are carefully removed by a highly trained scientist. The scientist will then record information about each bird, such as its species, sex and age, and take measurements, such as its weight and the length of its wings. These measurements help researchers determine how healthy a bird is. A scientist then puts a uniquely numbered aluminum band, and sometimes also colored plastic bands, on the bird's legs. Finally, the bird is released.
When a banded bird is caught again in the future, researchers can learn important information about that bird's life, such as how far it travels and how long it lives. The band numbers of re-caught birds are always reported to the BBL, which compiles the information on where and when each bird is re-caught.
In most studies, researchers encounter less than one in five banded birds between seasons. These chances get increasingly smaller the farther birds travel from the location where they were banded. Because the chances of encountering a banded bird again can be low, banding data is of limited use when it comes to tracking migratory birds throughout their annual cycle. Despite these limitations, banding can be a very useful tool for studying non-migratory birds or birds in their wintering or breeding territory.