Common kestrels are widespread birds of prey; they are small compared with other raptors, but larger than most songbirds. Common kestrels are mainly light chestnut brown in color with blackish spots on the upperside and buff with narrow blackish streaks on the underside; the remiges are also blackish. The males have fewer black spots and streaks and their cap and tail are blue-grey. 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.
Common kestrels are found in Europe, Asia, and Africa. These birds are sedentary but in the cold parts of their range, they migrate south in winter. Common kestrels live in open habitats such as tundra, taiga, grassland, shrubland, marshland, fields, and heaths. They can also be found in forested areas and readily adapt to human settlement, as long as sufficient swathes of vegetation are available, and may even be found in wetlands, moorlands, and arid savanna.
Common kestrels are generally solitary birds and are seen in pairs only during the breeding season. They are diurnal hunters. When hunting, Common kestrels hover about 10-20 m (33-66 ft) above the ground, searching for prey, either by flying into the wind or by soaring using ridge lift. These birds have very keen eyesight that allows them to spot small prey from a distance. Once prey is sighted, the bird makes a short, steep dive toward the target. It can often be found hunting along the sides of roads and motorways. Another favorite hunting technique is to perch a bit above the ground cover, surveying the area. When the birds spot prey animals moving by, they will pounce on them. Common kestrels communicate with the help of various calls. When alarmed they utter 'kii-kii-kiikii' and in flight, the birds produce a 'kik-kik' call.
Common kestrels are carnivores and eat almost exclusively small mammals such as voles, shrews and true mice. They will also hunt birds, bats, swifts, frogs, lizards, and insects.
Common kestrels are monogamous and form long-lasting pair bonds. They start breeding in April or May in temperate Eurasia and between August and December in the tropics and southern Africa. Common kestrels nest in cavities, preferring holes in cliffs, trees or buildings; in built-up areas, the birds will often nest on buildings and will reuse the old nests of other birds. Common kestrels are usually solitary nesters but may sometimes nest in loose colonies. The female lays a clutch of 3 to 7 eggs. Incubation lasts around 4 weeks, and only the female incubates the eggs. The male is responsible for providing her with food, and for some time after hatching this remains the same. Later, both parents share brooding and hunting duties until the young fledge, after 4-5 weeks. The family stays close together for a few weeks, during which time the young learn how to fend for themselves and hunt prey. They become reproductively mature and are ready to breed for the first time by the next breeding season.
In the mid-20th century populations of Common kestrels declined due to heavy use of organochlorine and other pesticides. At present, these birds of prey are not considered globally threatened, however, in some areas they still suffer from pesticides as well as from habitat degradation and decline of their primary small mammal prey.
According to the IUCN Red List, the total Common kestrels' population size is around 4,000,000-6,500,000 mature individuals. The European population consists of 409,000-603,000 pairs, which equates to 819,000-1,210,000 mature individuals. According to the European Raptors Biology and Conservation resource, the European population of the species is between 330,000 and 500,000 pairs. Largest populations are in Germany: 41,500 - 68,000 pairs; France: 72,000 - 101,000 pairs; UK: 36,800 pairs; Russia: 40,000 - 60,000 pairs and Spain: 25,000 -30,000 pairs. Currently, Common kestrels are classified as Least Concern (LC) on the IUCN Red List but hteir numbers today are decreasing.
Common kestrels play a very important role in their ecosystem; these birds help control agricultural pests such as voles and mice as they make up the biggest part of their diet.