There are five species of falcons in Canada and they can be distinguished from other birds of prey by the tooth-like projection near the tip of the upper half of the bill. They also are generally smaller and more streamlined than other bird-of-prey species.
Adaptations that have enabled falcons to become highly specialized predators include a small rounded head, a compact body, long pointed wings and powerful taloned feet.
The peregrine falcon is a crow-sized falcon. Adult males are 38 to 46 cm long and weigh on average 570 grams while the larger females are 46 to 54 cm long and approximately 910 grams. Juvenile peregrines are the same size as the adults by the time they are 60 days old.
The most reliable distinguishing feature of the adult peregrine falcon is the dark malar stripe (or "moustache") below the eye and the dark bluish-grey or slate-coloured crown, back and upper surface of the wings.
The dark feathers on the head look like a cap with chinstraps and are clearly visible at a distance. The throat, chest and underparts are white with blackish-brown horizontal bars on the sides, thighs, abdomen, underwings and lower breast area.
Anatum peregrines (the subspecies that lives in southern Canada) are noted for very dark heads and malar strips and they often have a rich rufous (rusty or salmon colour) on their breast during the breeding season.
Juvenile peregrines are brown where the adults are dark and are golden-brown where the adults are white. Instead of the horizontal barring of the adults, the juveniles have vertical streaks.