The merlin (Falco columbarius) is a small species of falcon from the Northern Hemisphere, with numerous subspecies throughout North America and Eurasia. A bird of prey, the merlin breeds in the northern Holarctic; some migrate to subtropical and northern tropical regions in winter. Males typically have wingspans of , with females being slightly larger. They are swift fliers and skilled hunters, which specialize in preying on small birds in the size range of sparrows to doves and medium-sized shorebirds. In recent decades, merlin populations in North America have been significantly increasing, with some merlins becoming so well adapted to city life that they forgo migration; in Europe, populations increased up to about 2000, but have been steady subsequently. The merlin has for centuries been well regarded as a falconry bird.
Nomenclature The scientific classification of the merlin (Falco columbarius) represents a crucial bridge between early colonial natural history and the birth of modern taxonomy. In the early 18th century, English naturalist Mark Catesby traveled through the American colonies and documented the bird under the colloquial name "pigeon hawk" in his groundbreaking Natural History of Carolina, Florida and the Bahama Islands (1729–1732). Decades later, Swedish botanist Carl Linnaeus used Catesby's detailed descriptions and illustrations to formally introduce the species in his 1758 tenth edition of Systema Naturae, assigning it the binomial name Falco columbarius with the vague type locality of "America". The generic name Falco stems from the Late Latin falx (meaning "sickle"), pointing to the bird's razor-sharp, hooked talons, while the specific epithet columbarius translates from Latin to "of or pertaining to doves", preserving Catesby’s early comparison to pigeons. However, the geographic scope of the species quickly expanded when English ornithologist Marmaduke Tunstall identified Eurasian populations as distinct in his 1771 work Ornithologica Britannica, assigning them the taxon Falco aesalon. Modern ornithological debates still simmer over whether the merlin should remain a single globally distributed species or split into distinct New World and Old World species; if such a formal taxonomic split is globally accepted, the Eurasian birds will officially reclaim Tunstall's designated name, Falco aesalon.
The linguistic journey of the common name "merlin" is entirely separate from the bird's scientific cataloging, tracing a path through centuries of European sound shifts and bird-hunting culture. The name ultimately derives from the Old French esmerillon, which traveled into English via the Anglo-Norman variants merilun or meriliun after the Norman Conquest. This French terminology evolved from much older, cognate Germanic words—such as the Middle Dutch smeerle, Old High German smerle, and Old Icelandic smyrill—all of which historically referred to small, agile birds of prey. The word was firmly integrated into the English vernacular by the late Middle Ages, as evidenced by its appearance in John Wycliffe's Bible translation around 1382, which lists "An Egle, & agriffyn, & a merlyon" among its birds. While the species was widely known in North America as the "pigeon hawk" well into the 20th century due to its physical resemblance to a pigeon in flight, the older European name "merlin" eventually reclaimed global dominance in standard ornithological checklists.
Despite the identical spelling and pronunciation, the falcon’s name bears absolutely no historical or etymological connection to the legendary Arthurian wizard Merlin. The wizard's name is actually an English adaptation of the ancient Welsh name Myrddin (meaning "sea fortress" or "dune"), which was Latinized as Merlinus by 12th-century cleric Geoffrey of Monmouth to avoid awkward associations with the French word merde. Because Geoffrey’s Latinized translation of the legendary figure grew popular around the same time that the Anglo-Norman language was actively reshaping the French esmerillon into merilun, the two entirely unrelated words organically converged in the English language. This linguistic coincidence created a permanent homophone, leading generations of folklore enthusiasts to mistakenly assume that either the wizard was named after the swift, fierce falcon or that the bird was named in honor of the court sorcerer.
Systematics
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 million years ago (Mya). As suggested by biogeographical and DNA sequence data, it might be part of an ancient nonmonophyletic radiation of Falco species 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. More recently, a genetic link to two tropical African species, grey kestrel Falco ardosiaceus and Dickinson's kestrel F. dickinsoni, has been found.
Supporting this ancient timeline, a fossil falcon was discovered in the Early Blancan (4.3–4.8 Mya) 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 merlin or its close relative. With its age quite certainly antedating the split between the Eurasian and North American merlins, the fossil falcon supports 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.
Subspecies 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. They are probably best considered distinct species, with gene flow having ceased at least 1 Mya, but probably more; but more study is required, particularly in the less-sampled subspecies, before a formal split can be made.
By and large, color variation in either group independently follows Gloger's rule. The Pacific temperate rain forest subspecies F. c. suckleyi males are almost uniformly black on the upperside and have heavy black blotches on the belly, whereas those of the lightest subspecies, F. c. pallidus, have little nondilute melanin altogether, with a gray upperside and reddish underside pattern. Nine subspecies are currently accepted:
American group (Falco columbarius sensu stricto) F. c. columbarius (Linnaeus, 1758) – taiga merlin, boreal merlin, tundra merlin Canada and northernmost United States east of Rocky Mountains, except Great Plains, migratory, winters in southern North America, Central America, the Caribbean, and northern South America from the Guyanas to the northern Andes foothills, rarely winters in the northern USA. F. c. richardsonii (Ridgway, 1871) – prairie merlin Great Plains from Alberta to Wyoming, resident (some winter dispersal), paler than F. c. columbarius F. c. suckleyi (Ridgway, 1873) – black merlin, coastal forest merlin Pacific coast of North America, from southern Alaska to northern Washington, resident (some altitudinal movements) Eurasian group (F. aesalon if split) F. c./aesalon subaesalon (C.L. Brehm, 1827) – Icelandic merlin Iceland and Faroe Islands, Faroese population has some gene flow with F. c. aesalon, resident or some winter dispersal to coasts F. c./a. 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 F. c. subaesalon, British Isles population resident or short-distance movement from moors to coasts, rest migratory; winters in continental Europe and the Mediterranean region to about Iran
F. c./a. pallidus (Sushkin, 1900) – pallid merlin, steppe merlin Asian steppes between Aral Sea and Altay Mountains, migratory, winters in south-central and northern South Asia F. c./a. insignis (Clark, 1907) – East Siberian merlin Siberia between Yenisei and Kolyma Rivers, migratory, winters in continental East Asia F. c./a. lymani (Bangs, 1913) – Central Asian merlin Mountains of eastern Kazakhstan and surrounding countries, short-distance migrant F. c./a. pacificus (Stegmann, 1929) – Pacific merlin Russian Far East to Sakhalin, migratory, winters in Japan, Korea, and nearby
Description
The merlin is long with a wingspan. Compared with most other small falcons, it is more robust and heavily built. Males average at about and females are typically about . Considerable variation, however, is seen throughout the birds' range, and in particular in migratory populations, over the course of a year. Thus, adult males may weigh and females . Each wing measures , the tail measures and the tarsi measure . Such sexual dimorphism is common among raptors; it allows males and females to hunt different prey animals and decreases the territory size needed to feed a mated pair.
The male merlin has a blue-gray back, ranging from almost black to silver-gray in different subspecies. His underparts are buff- to orange-tinted and more or less heavily streaked with black to reddish brown. The female and immature are brownish-gray to dark brown above, and whitish buff spotted with brown below. Besides a weak whitish supercilium and the faint dark malar stripe—which are barely recognizable in both the palest and the darkest birds—the face of the merlin is less strongly patterned than in most other falcons. Nestlings are covered in pale buff down feathers, shading to whitish on the belly.
The remiges are blackish, and the tail usually has some three or four wide, blackish bands, too. Very light males only have faint and narrow medium-gray bands, while in the darkest birds, the bands are very wide, so that the tail appears to have narrow lighter bands, instead. In all of them, however, the tail tip is black with a narrow white band at the very end, a pattern possibly plesiomorphic for all falcons. Altogether, the tail pattern is quite distinct, though, resembling only that of the aplomado falcon (F. berigora) and (in light merlins) some typical kestrels. The eye and beak are dark, the latter with a yellow cere. The feet are also yellow, with black claws.
Light American males may resemble the American kestrel (F. sparverius, not a typical kestrel), but merlin males have a gray back and tail rather than the reddish-brown of the kestrels. Light European males can be distinguished from kestrels by their mainly brown wings. In the north of South Asia, wintering males may be confused with the red-necked falcon (F. chicquera) if they fly away from the observer and the head (red on top in F. chicquera) and underside (finely barred with black in F. chicquera) are not visible.
Ecology