The Merlin is a small, dashing falcon that breeds throughout the northern forests and prairies of North America, Europe, and Asia. Only slightly larger than the more common American Kestrel (Falco sparverius), it is heavier and in flight often appears considerably larger. The sexes differ in adult plumage, with females noticeably larger than males. This falcon was previously called the "Pigeon Hawk" because in flight it can be mistaken for a member of the pigeon family; its species name (columbarius) also refers to pigeons. "Merlin" derives from esmerillon, the Old French name for this species. There are three North American subspecies: the Black Merlin (F. c. suckleyi) from the Pacific Northwest, the Taiga (or better-named Boreal) Merlin (F. c. columbarius) of northern forests, and the Prairie Merlin (F. c. richardsonii), a pale colored form that breeds in northern prairies and aspen parkland of the U.S and southern Canada.
Primarily monogamous, the Merlin raises one brood each breeding season, laying its eggs in the abandoned nests of crows or hawks. It feeds predominantly on small birds, which it generally catches in short, quick flights. Within the last 30 years, breeding populations have colonized an increasing number of urban centers, particularly in the northern Great Plains. This development of urban populations occurred at the same time as the species underwent a substantial recovery from its post-DDT era population low, when many rural populations disappeared.
Although its small size makes the Merlin unsuitable for hawking large quarry, in Medieval Europe it became popular as a "lady's hawk" and was used in the now classical ringing flights directed at the Skylark (Alauda arvensis). Catherine the Great and Mary Queen of Scots were among the more famous enthusiasts of this sport. These lark flights have continued as a tradition in Great Britain, although falconers are now under public pressure to stop the sport. In North America, a small number of falconers fly Merlins at avian quarry ranging from sparrows to doves. Although not nearly as popular as the larger species, their speed and tremendous heart have earned them a loyal following.
Breeding studies have been conducted on Merlin populations across its North American range, except for the west coast subspecies. Particularly well-studied are Merlins resident in urban centers on the northern Great Plains. Substantial contributions have been made through long-term studies of rural populations in Britain and Sweden.