Other raptors may also move their tail when excited, but tend to wag it from side to side instead. As in most species of raptors, females are considerably larger than males. Plumage differences between males and females are minor. Males tend to have a slightly whiter breast and somewhat fainter barring on the belly, while females often are slightly browner on the back. The size and shape of the moustache is slightly different on each Peregrine, and allows individuals to be identified much like fingerprints of humans.
Peregrines are dark on the back, and usually have a light breast and a heavily barred belly.
In flight, their dark underwing is often noticeable. Immatures also generally have rather brownish plumage on their backs, in contrast to the adults which are gray or black. Worldwide scientists have recognized twenty-two races of the Peregrine Falcon. The three North American subspecies vary considerably in appearance and are described individually below. The Tundra Peregrine is the palest of the North American subspecies, and also is slightly smaller than the others.