Aesalon columbarius(Linnaeus,1758) Falco aesalonTunstall, 1771 (but see text)
Themerlin (Falco columbarius) is a smallspecies offalcon from theNorthern Hemisphere,[2] with numerous subspecies throughout North America andEurasia. Abird of prey, the merlin breeds in the northernHolarctic; somemigrate tosubtropical and northerntropical regions in winter. Males typically have wingspans of 53–58 centimetres (21–23 in), with females being slightly larger. They are swift fliers and skilled hunters which specialize in preying on small birds in the size range ofsparrows todoves and medium-sizedshorebirds. 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.[3] The merlin has for centuries been well regarded as afalconry bird.
The merlin was described and illustrated by the English naturalistMark Catesby (as the "pigeon hawk") in hisNatural history of Carolina, Florida and the Bahama Islands published in 1729–1732.[4][5] Based on this description, in 1758Carl Linnaeus included the species in thetenth edition of hisSystema Naturae and introduced the presentbinomial nameFalco columbarius with thetype locality as "America".[6] The genus name isLate Latin;falco derives fromfalx,falcis, asickle, referring to the claws of the bird.[7] The species namecolumbarius isLatin for "of doves" from "columba", "dove".[8] Thirteen years after Linnaeus's descriptionMarmaduke Tunstall recognized the Eurasian birds as a distincttaxonFalco aesalon in hisOrnithologica Britannica. If two species of merlins are recognized, theOld World birds would thus bear thescientific nameF. aesalon.[9][10]
The name "merlin" is derived fromOld Frenchesmerillon viaAnglo-Normanmerilun ormeriliun. There are related Germanic words derived through older forms such asMiddle Dutchsmeerle,Old High Germansmerle andOld Icelandicsmyrill.[11]Wycliffe's Bible, around 1382, mentionsAn Egle, & agriffyn, & a merlyon.[11] The species was once known as "pigeon hawk" in North America.[12]
Although the merlin's name looks and sounds like the name of the wizardMerlin prominent in Arthurian legend, the bird is not named after the wizard.[13] The wizard's name is an English cognate of theWelsh 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. Thered-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 theEarly Pliocene, some 5 Ma (million years ago). As suggested bybiogeography andDNA sequence data, it might be part of an ancient non-monophyleticradiation ofFalco species from Europe toNorth America, alongside the ancestors of forms such as theAmerican kestrel (F. sparvierus), and theaplomado falcon (F. femoralis) and its relatives. A relationship with thered-necked falcon (F. chicquera) was once proposed based on theirphenetic similarity, but this is not considered likely today.[9][10][14][15][16] More recently, a genetic link to two tropical African species,grey kestrelFalco ardosiaceus anddickinson's kestrelF. dickinsoni has been found.[17]
In that regard, afossil falcon from the EarlyBlancan (4.3–4.8 Ma)[18]Rexroad Formation ofKansas. Known from an almost complete rightcoracoid (specimenUMMP V29107) and sometarsometatarsus,tibiotarsus andhumerus 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, the fossil falcon supports the idea of the merlin lineage originating in North America, or rather the colonization thereof. Afteradapting to itsecological niche, ancient merlins would have spread to Eurasia again, withgene flow being interrupted as theBeringia andGreenland regions became icebound in theQuaternary glaciation.[10][14][19]
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, withgene flow having ceased at least a million years ago, but probably more;[10][17] but more study is required, particularly in the less-sampled subspecies, before a formal split can be made.[20]
By and large, color variation in either group independently followsGloger's Rule. ThePacific temperate rain forest subspeciesF. c. suckleyi males are almost uniformly black on the upperside and have heavy black blotches on the belly, whereas those of the lightestsubspecies,F. c. pallidus, have little non-dilutemelanin altogether, with gray upperside and reddish underside pattern.[9] Nine subspecies are currently accepted:[20]
Coastal forest merlin (F. c. suckelyi), Lake Los Carneros Park, Goleta,California, United States
Northern Eurasia fromBritish Isles throughScandinavia to centralSiberia. Population of northernBritain shows evidence ofgene flow fromF. c. subaesalon. British Isles population resident or short-distance movement from moors to coasts, rest migratory; winters inEurope and theMediterranean region to aboutIran.
The merlin is 24–33 cm (9.4–13.0 in) long with a 50–73 cm (20–29 in) wingspan.[22] Compared with most other smallfalcons, it is more robust and heavily built. Males average at about 165 g (5.8 oz) and females are typically about 230 g (8.1 oz). There is considerable variation, however, throughout the birds' range and—in particular inmigratory populations—over the course of a year. Thus, adult males may weigh 125–210 g (4.4–7.4 oz), and females 190–300 g (6.7–10.6 oz). Each wing measures 18.2–23.8 cm (7.2–9.4 in), the tail measures 12.7–18.5 cm (5.0–7.3 in) and thetarsus measures 3.7 cm (1.5 in).[22][23] Suchsexual dimorphism is common amongraptors; it allows males and females to hunt differentprey animals and decreases theterritory size needed to feed a mated pair.[9][24]
The male merlin has a blue-gray back, ranging from almost black tosilver-gray in differentsubspecies. Its underparts arebuff- 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 whitishsupercilium and the faint darkmalar 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 buffdown feathers, shading to whitish on the belly.[24]
Theremiges are blackish, and the tail usually has some three to 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 possiblyplesiomorphic for all falcons. Altogether, the tail pattern is quite distinct though, resembling only that of theaplomado falcon (F. berigora) and (in light merlins) some typicalkestrels. The eye andbeak are dark, the latter with a yellowcere. The feet are also yellow, with black claws.[24]
Light American males may resemble theAmerican 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 ofSouth Asia, wintering males may be confused with thered-necked falcon (F. chicquera) if they fly away from the observer and the head (red on top inF. chicquera) and underside (finely barred with black inF. chicquera) are not visible.[24]
Merlins inhabit fairly open country, such aswillow orbirch scrub,shrubland, but alsotaiga forest,parks,grassland such assteppe andprairies, ormoorland. They are not veryhabitat-specific and can be found fromsea level to thetreeline. In general, they prefer a mix of low and medium-height vegetation with some trees, and avoid dense forests as well as treelessarid regions. Duringmigration however, they will utilize almost any habitat.[9]
Most of its populations are migratory, wintering in warmer regions. Northern European birds move to southernEurope andNorth Africa, and North American populations to the southern United States to northernSouth America. In the mildermaritime parts of its breeding range, such asGreat Britain, thePacific Northwest and westernIceland, as well as inCentral Asia, it will merely desert higher ground and move to coasts and lowland during winter. The migration to the breeding grounds starts in late February, with most birds passing through the US,Central Europe and southernRussia in March and April, and the last stragglers arriving in the breeding range towards the end of May. Migration to winter quarters at least in Eurasia peaks in August/September, while e.g. inOhio, just south of the breeding range,F. c. columbarius is typically recorded as a southbound migrant as late as September/October.[9][21] In Europe, merlins will roost communally in winter, often withhen harriers (Circus cyaneus). In North America,communal roosting is rare.
Merlins rely on speed and agility to hunt their prey. They often hunt by flying fast and low, typically less than 1 m (3.3 ft) above the ground, using trees and large shrubs to take prey by surprise. But they actually capture most prey in the air, and will "tail-chase" startled birds. Throughout its native range, the merlin is one of the most able aerial predators of small to mid-sized birds, more versatile if anything than the largerhobbies (which prefer to attack in mid-air) and the more nimblesparrowhawks (which usually go for birds resting or sleeping in dense growth). Breeding pairs will frequently hunt cooperatively, with one bird flushing the prey toward its mate.[9][25]
The merlin will readily take prey that is flushed by other causes, and can for example be seen tagging alongsharp-shinned hawks (Accipiter striatus) to catch birds that escape from this ambush predator into the open air. It is quite unafraid, and will readily attack anything that moves conspicuously. Merlins have even been observed trying to "catch"automobiles andtrains, and to feed on captive birds such as those snared in themist nets used byornithologists. Even under adverse conditions, one in 20 targets is usually caught, and under good conditions almost every other attack will be successful. Sometimes, merlinscache food to eat it later.[9][26]
In particular during the breeding season, most of the prey are smallish birds weighing 10–40 g (0.35–1.41 oz). Almost any suchspecies will be taken, with local preferences for whatever is most abundant—be itlarks (Alaudidae),pipits (Anthus),finches (Fringillidae),[27]house sparrows (Passer domesticus), otherOld World sparrows (Passeridae),northern wheatears (Oenanthe oenanthe),thrushes (Turdus),kinglets (Regulidae)[28] orbuntings (Emberiza)[27]—and inexperiencedyearlings always a favorite. Smaller birds will generally avoid a hunting merlin if possible. In theCayman Islands (where it only occurs in winter),bananaquits were noted to die of an apparentheart attack orstroke, without being physically harmed, when a merlin went at them and they could not escape.[26]
Corvids are the primary threat to eggs and nestlings. Adult merlins may be preyed on by largerraptors, especiallyperegrine falcons (F. peregrinus),eagle-owls (e.g.,great horned owl,Bubo virginianus), and largerAccipiterhawks (e.g.,northern goshawk,A. gentilis). In general however,carnivorous birds avoid merlins due to their aggressiveness and agility. Their desire to drive larger raptors away from their territory is so pronounced that it is an identifying characteristic. Quoting from one popular raptor watching reference,[40] "An observer may use this aggressive tendency for identification purposes and as a means of detection. High-flying merlins often betray themselves and distinguish themselves because they are vigorously harassing another raptor (even ones as large as the Golden Eagle)."
Breeding occurs typically in May/June. Though the pairs aremonogamous at least for a breeding season,extra-pair copulations have been recorded. Most nest sites have dense vegetative or rocky cover; the merlin does not build a proper nest of its own. Most will use abandonedcorvid (particularlyCorvus crow andPica magpie) orhawk nests which are inconifer or mixed tree stands. Inmoorland—particularly in theUK—the female will usually make a shallow scrape in denseheather to use as a nest. Others nest in crevices on cliff-faces and on the ground, and some may even use buildings.[9]
Three to six (usually 4 or 5) eggs are laid. The rusty brown eggs average at about 40 mm × 31.5 mm (1.57 in × 1.24 in).[citation needed] The incubation period is 28 to 32 days.Incubation is performed by the female to about 90%; the male instead hunts to feed the family.Hatchlings weigh about 13 g (0.46 oz). The youngfledge after another 30 days or so, and are dependent on their parents for up to 4 more weeks. Sometimes first-year merlins (especially males) will serve as a "nest helper" for an adult pair. More than half—often all or almost all—eggs of aclutch survive to hatching, and at least two-thirds of the hatched young fledge. However, as noted above, in years with little supplementary food only 1 young in 3 may survive to fledging. The merlin becomessexually mature at one year of age and usually attempts to breed right away. The oldest wild bird known as of 2009 was recorded in its 13th winter.[9][41]
A malesmyril is featured on thisFaroese stamp by Edward Fuglø
John James Audubon illustrated the merlin in the second edition ofBirds of America (published in London, 1827–38) as Plate 75, under the title, "Le Petit Caporal –Falco temerarius". The image was engraved and colored byRobert Havell's London workshops. The original watercolor by Audubon was purchased by the New York History Society,[42] where it remains as of January 2009.
William Lewin illustrates the merlin as Plate 22 in volume 1 of hisBirds of Great Britain and their Eggs, published 1789 in London.
In medieval Europe, merlins were popular infalconry: theBook of St. Albans listed it as "the falcon for a lady", where it was noted for classic "ringing" (circling rapidly upward) pursuits of the English skylark.[43] Though the merlin is only slightly larger than theAmerican kestrel in dimensions, it averages about one third to one half larger by weight, with this weight mostly being extra muscle that gives it greater speed and endurance than the kestrel.[43] Like the American kestrel, the merlin offers the modern falconer the ability to hunt year round against sparrows and starlings, in urban settings not requiring large tracts of land or hunting dogs, with the additional advantage of being able to reliably take small game birds such as dove and quail during hunting season. A large and exceptionally aggressive female merlin may take prey as large as pigeons and occasionally even small ducks.[44] They also offer an exciting style of flight, generally at closer range than large falcons where it may be more clearly witnessed and enjoyed by the falconer. In addition to horizontal tail-chases in the manner of American kestrels, they will also "ring up" in pursuit of prey that seeks to escape by out-climbing them, and perform high speed diving stoops on prey beneath them in the manner of larger falcons. Quoting from one popular falconry book on the eagerness of merlins to chase a swung lure, "Every stoop, outrun, dodge, and aerial maneuver of a hard flight to real quarry can be duplicated with no risk of loss of the falcon. Merlins regularly flown to the lure take most field quarries with such ease and such assurance as to make the field flight the less interesting and exciting of the two."[43]
Quoting expert falconer Matthew Mullenix, author of the book "American Kestrels in Modern Falconry", in an article comparing the American kestrel to the merlin he states "What a merlin gives you is raw power: lots of it. It brings an ability to negate wind as a factor, to stay airborne at a tremendous clip then gear down further at any time for more performance. One merlin can dominate an entire flock of frightened birds, directing its fate as a whole. The flock responds like bait fish to a barracuda and for precisely the same reason. Merlins demonstrate total mastery of their element."[45] Concerning suitable game for these two species, he states "To snipe, dove, quail and open-country sparrows, merlins are best suited. For most blackbirds (Icteridea), either falcon can prove effective. Starlings in close are extremely vulnerable to kestrels; but in the open are best prey for merlins."
Hunter with trained merlin, Jandari Lake,Georgia SSR, November 1979
Altogether, the merlin is not particularly rare, and due to this and its wide range it is considered a species ofleast concern by theIUCN.[1] Its numbers are—except in theAsian part of its range, where the situation is less well determined—regularlycensused. In about every major country it inhabits, many hundreds to many thousands are found, ranging from a "mere" 250–300 pairs inBelarus to perhaps as many as 30,000 pairs ofaesalon inEuropean Russia as determined in 1993. It is listed onCITES Appendix II and on a local level protected as otherbirds of prey; while some countries allow to capture merlins, e.g. for falconry, international trade requires an export permit.[1][9]
By far the most serious long-term threat to these birds ishabitat destruction, especially in their breeding areas. Ground-nesting populations inmoorland have a preference for tall heather, and are thus susceptible to overmanagement by burning vast tracts instead of creating ahabitat mosaic containing old and new growth. Still, the merlin is rather euryoecious (adaptable to various conditions) and will even live in settled areas, provided they have the proper mix of low and high vegetation, as well as sufficient prey (which is usually the case) and nesting sites (which is a common limiting factor).[9]
In North America, the species seems to have been more widespread in the past, or perhaps its range has shifted northwards:F. c. columbarius was an uncommon breeding bird inOhio before the 20th century, but inSeneca County, as early as the 1900s even single adults were rarely seen in the breeding season. It is encountered in Ohio as a passage migrant and rarely as a winter guest, though two recent nestings have been confirmed. Changing land-use in Ohio mainly turned forest intoagricultural land and thus is not very likely to have rendered the region inhospitable to the merlin;global warming on the other hand cannot be dismissed as a reason, given that the merlin is essentially asubarctic species that barely ranges even intotemperate climes. Also, it may be that the number of merlins wintering in the northern USA has increased during the 20th century.[12][9][21]
Perhaps the most frequent cause of accidental death for individuals is collision with man-made objects, particularly during attacks. This may account for almost half of all premature deaths of merlins. In the 1960s and 1970s,organochlorine pesticides were responsible for declines—particularly inCanada—due to eggshell thinning and subsequent brood failure, and compromising theimmune system of adults. This has since been remedied with restrictions on the use ofDDT and similar chemicals, and numbers have rebounded. Overall, merlin stocks appear globally stable; while they may decline temporarily in places, they will usually increase again eventually, suggesting that this phenomenon is due to the fluctuations of supplementary food stocks discussed above.[9]
^Groombridge, Jim J.; Jones, Carl; Bayes, Michelle K.; van Zyl, Anthony J.; Carrillo, José; Nichols, Richard A.; Bruford, Michael W. (2002). "A molecular phylogeny of African kestrels with reference to divergence across the Indian Ocean".Molecular Phylogenetics and Evolution.25 (2):267–277.Bibcode:2002MolPE..25..267G.doi:10.1016/S1055-7903(02)00254-3.PMID12414309.
^abFuchs, Jérôme; Johnson, Jeff A.; Mindell, David P. (2015). "Rapid diversification of falcons (Aves: Falconidae) due to expansion of open habitats in the Late Miocene".Molecular Phylogenetics and Evolution.82:166–182.doi:10.1016/j.ympev.2014.08.010.
^abFerguson-Lees, James; Christie, David A. (2001).Raptors of the World. Boston: Houghton Mifflin.ISBN0-618-12762-3.
^Davis, Kate (2002).Falcons of North America. Mountain Press Publishing Company.
^abcdWhite, Clayton M.; Olsen, Penny D.; Kiff, Lloyd F. (1994). "Family Falconidae". In del Hoyo, J.; Elliot, A.; Sargatal, J. (eds.).Handbook of Birds of the World. Vol. 2: New World vultures to Guineafowl): 216–275, plates 24–28. Barcelona: Lynx Edicions.ISBN84-87334-15-6.
^Ferguson-Lees, J. & Christie, D.A. & Franklin, K. & Mead, D. & Burton, P.. (2001). Raptors of the world. Helm Identification Guides.
^Mikula, P.; Morelli, F.; Lučan, R. K.; Jones, D. N.; Tryjanowski, P. (2016). "Bats as prey of diurnal birds: a global perspective".Mammal Review.46 (3):160–174.doi:10.1111/mam.12060.
^Ferguson-Lees, J. & Christie, D.A. & Franklin, K. & Mead, D. & Burton, P.. (2001). Raptors of the world. Helm Identification Guides.
^Ferguson-Lees, J. & Christie, D.A. & Franklin, K. & Mead, D. & Burton, P.. (2001). Raptors of the world. Helm Identification Guides.
"Falco columbarius, Pigeon Hawk"; fromAmerican Ornithology 2nd edition, volume 1 (1828) by Alexander Wilson and George Ord.Color plate from 1st edition by A. Wilson.
"The Pigeon Hawk" and "Le Petit Caporal", John James Audubon,Ornithological Biography volume 1 (1831). AtPigeon Hawk; Petit Caporal, in the appendix toOrnithological Biography volume 5 (1839), Audubon notes that hisFalco temerarius of volume 1 was a small male merlin, and that this was brought to his attention byCharles Bonaparte, nephew of "thelittle corporal".Illustration fromBirds of America octavo edition, 1840.
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