Bird ringing or bird banding is the attachment of small, individually numbered metal or plastic tag to the leg or wing of a wild bird to enable individual identification. This helps in keeping track of the movements of the bird and their life history. It is common to take measurements and examine condition of feather moult, subcutaneous fat, age indications and sex during capture for ringing. The subsequent recapture or recovery of the bird can provide information on migration, longevity, mortality, population studies, territoriality, feeding behaviour, and other aspects that are studied by ornithologists. Other methods of marking birds may also be used to allow for field based identification that does not require capture.
The earliest recorded attempt to mark a bird was made by Quintus Fabius Pictor. These Roman officers, during the Punic Wars around 218–201 BC, were sent a crow by a besieged garrison, which suggests that this was an established practice. Pictor used a thread on the bird's leg to send a message back. A knight interested in chariot races during the time of Pliny (AD 1) would take crows to Volterra, 135 miles (217 km) away and release them with information on the race winners. L'Ecuyer went on to mark hundreds of crows in his lifetime while Pictor's interest quickly waned.