During most of the year merlins inhabit open country ranging from marshlands to deserts, but many breed in conifer and birch woods. In open country eggs are laid in a scrape on the ground amid bushes, but in forested areas the tree nests of crows, rooks, or magpies are used. Its diet consists mainly of smaller birds that it catches in midair. Unlike the peregrine falcon, the merlin does not dive at prey but accelerates after it; rodents and insects are also eaten. An aggressive, fearless hunter, the merlin has long been used in falconry.

In North America, where merlins were formerly called pigeon hawks, breeding occurs from northwestern Alaska south through most of Canada and the western United States as far east as Oregon, Idaho, and South Dakota. Very dark-coloured populations breed in western British Columbia. In Europe merlins breed in the British Isles, Iceland, and Russia. During the winter most migrate to regions just south of the breeding range, although some individuals fly as far as northern South America and northern Africa.