dic smyrill. Wycliffe's Bible, around 1382, mentions An Egle, & agriffyn, & a merlyon. The species was once known as 'pigeon hawk' in North America. The same name, associated with the legendary Wizard Merlin from the Arthurian legends, is a coincidence. The Wizard's name is an English cognate of the Welsh name “Myrddin” and is unrelated to the name of the bird.
The relationships of the merlin are not resolved to satisfaction. In size, shape and coloration, it is fairly distinct among living falcons. The red-necked falcon is sometimes considered more closely related to the merlin than other falcons, but this seems to be a coincidence due to similar hunting habits; it could not be confirmed in more recent studies. Indeed, the merlin seems to represent a lineage distinct from other living falcons since at least the Early Pliocene, some 5 Ma (million years ago). As suggested by biogeography and DNA sequence data, it might be part of an ancient non-monophyletic radiation of Falcos from Europe to North America, alongside the ancestors of forms such as the American kestrel (F. sparvierus), and the aplomado falcon (F. femoralis) and its relatives. A relationship with the red-necked falcon (F. chicquera) was once proposed based on their phenetic similarity, but this is not considered likely today.
In that regard, a fossil falcon from the Early Blancan (4.3–4.8 Ma) Rexroad Formation of Kansas. Known from an almost complete right coracoid (specimen UMMP V29107) and some tarsometatarsus, tibiotarsus and humerus pieces (V27159, V57508-V57510, V57513-V57514), this prehistoric falcon was slightly smaller than a merlin and apparently a bit more stout-footed, but otherwise quite similar. It was part of the Fox Canyon and Rexroad Local Faunas, and may have been the ancestor of the living merlins or its close relative. With its age quite certainly pre-dating the split between the Eurasian and North American merlins, it agrees with the idea of the merlin lineage originating in North America, or rather the colonization thereof. After adapting to its ecological niche, ancient merlins would have spread to Eurasia again, with gene flow being interrupted as the Beringia and Greenland regions became icebound in the Quaternary glaciation.
That the merlin has a long-standing presence on both sides of the Atlantic is evidenced by the degree of genetic distinctness between Eurasian and North American populations. Arguably, they might be considered distinct species, with gene flow having ceased at least a million years ago, but probably more.
By and large, color variation in either group independently follows Gloger's Rule. The Pacific temperate rain forest subspecies suckleyi's males are almost uniformly black on the upperside and have heavy black blotches on the belly, whereas those of the lightest subspecies, pallidus, have little non-dilute melanin altogether, with grey upperside and reddish underside pattern.
- Falco columbarius columbarius (Linnaeus, 1758) – taiga merlin, boreal merlin, tundra merlin
- Canada and northernmost United States east of Rocky Mountains, except Great Plains. Migratory, winters in S North America, Central America, the Caribbean, and N South America from the Guyanas to the northern Andes foothills. Rarely winters in the northern USA.
- Falco columbarius richardsonii (Ridgway, 1871) – prairie merlin
- Falco columbarius suckleyi (Ridgway, 1873) – black merlin, coastal forest merlin
- Pacific coast of North America, from S Alaska to N Washington state. Resident (some altitudinal movements).
- Falco columbarius/aesalon aesalon (Tunstall, 1771) – Eurasian merlin
- Northern Eurasia from British Isles through Scandinavia to central Siberia. Population of northern Britain shows evidence of gene flow from subaesalon. British Isles population resident, rest migratory; winters in Europe and the Mediterranean region to about Iran.
- Falco columbarius/aesalon subaesalon (C.L. Brehm, 1827) – Icelandic merlin, smyril (Faroese), smyrill (Icelandic)
- Iceland and Faroe Islands. Latter population has some gene flow with aesalon. Resident 