Common kestrels measure 32–39 cm (12+1⁄2–15+1⁄2 in) from head to tail, with a wingspan of 65–82 cm (25+1⁄2–32+1⁄2 in). Females are noticeably larger, with the adult male weighing 136–252 g (4+3⁄4–8+7⁄8 oz), around 155 g (5+1⁄2 oz) on average; the adult female weighs 154–314 g (5+3⁄8–11+1⁄8 oz), around 184 g (6+1⁄2 oz) on average. They are thus small compared with other birds of prey, but larger than most songbirds. Like the other Falco species, they have long wings as well as a distinctive long tail.
Their plumage is mainly light chestnut brown with blackish spots on the upperside and buff with narrow blackish streaks on the underside; the remiges are also blackish. Unlike most raptors, they display sexual colour dimorphism with the male having fewer black spots and streaks, as well as a blue-grey cap and tail. The tail is brown with black bars in females, and has a black tip with a narrow white rim in both sexes. All common kestrels have a prominent black malar stripe like their closest relatives.
The cere, feet, and a narrow ring around the eye are bright yellow; the toenails, bill and iris are dark. Juveniles look like adult females, but the underside streaks are wider; the yellow of their bare parts is paler. Hatchlings are covered in white down feathers, changing to a buff-grey second down coat before they grow their first true plumage.
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