In addition to the size difference, Gyrfalcons can be told apart from Peregrines by their lighter underwings and narrow or absent moustaches. This makes it possible to track the movements of individuals and gain valuable knowledge about their migratory routes and dispersal patterns. It also enables researchers to analyze the bloodlines of individual birds if the identity and history of both parents is known. As a result, it is possible to detect whether inbreeding is occurring in populations, and whether subspecies are hybridizing. Characters used are letters and numbers, and may either be vertical or tipped 90 degrees to the left.
Some bands also have a one millimetre thick white band separating the two characters.