Merlin

Name and taxonomy

The English naturalist Mark Catesby recorded the bird in the American colonies as the pigeon hawk. Carl Linnaeus used his account to name the species Falco columbarius in 1758. Falco comes from the Latin falx, a sickle, which points at the hooked talons. The word columbarius means of the doves, and it keeps Catesby's comparison with a pigeon. Marmaduke Tunstall named the Eurasian birds Falco aesalon in 1771.

The common name comes from the Old French esmerillon, by way of Anglo-Norman forms such as merilun. Older Germanic words, including Middle Dutch smeerle and Old Icelandic smyrill, lie behind the French one. The English name is old, and it appears in the Wycliffe Bible around 1382. The name has no link at all to the Arthurian wizard, whose name comes from Welsh Myrddin. The two words only became homophones because both entered English at the same period.

Evolution and relatives

The merlin sits apart from the other living falcons in size, shape and colour. Its line appears to have stood apart since early in the Pliocene, roughly 5 million years back. An old idea tied it to the red-necked falcon, but the likeness comes from a shared hunting style. Recent genetic work instead links it to the grey kestrel and Dickinson's kestrel of Africa.

A fossil falcon from Kansas, dated 4.3 to 4.8 million years ago, was slightly smaller than a merlin. It may be the ancestor of the living bird, which suggests the line began in North America. Merlins then spread back into Eurasia, and the ice ages cut the two groups apart. Gene flow stopped at least a million years ago, and the two groups may be separate species. Nine subspecies are accepted for now, three in America and six across Eurasia.

Appearance

A merlin is 24 to 33 centimetres long with a wingspan of 50 to 73 cm. Males average about 165 grams and females about 230 g. Weights vary widely, from 125 to 210 grams in males and 190 to 300 g in females. That gap in size lets a pair hunt different prey and keeps the territory they need smaller. The bird is stockier and more solid than other small falcons.

The male has a blue-grey back that ranges from silver to near black across the subspecies. His underside is buff to orange and streaked with black or reddish brown. Females and young birds are brownish grey to dark brown above and spotted brown below. The tail carries three or four wide dark bands and ends in black with a narrow white tip. The eye and bill are dark, the cere is yellow, and the yellow feet carry black claws.

Habitat and range

The merlin breeds right across the northern Holarctic, in North America and Eurasia. It uses open country: willow and birch scrub, taiga, steppe, prairie, moorland and parkland. It is found from sea level up to the treeline and avoids dense forest and bare desert. A mix of low and medium vegetation with a few trees suits it best. GBIF holds records from 145 countries and territories.

Most populations migrate, and northern European birds winter in southern Europe and North Africa. North American birds winter from the southern United States to northern South America. Birds in Britain, Iceland and the Pacific Northwest only drop from high ground to the coast. Return migration starts in late February, and the last birds reach the breeding range in May. European merlins roost together in winter, often with hen harriers, which North American birds rarely do.

Diet and hunting

The merlin lives on small birds, and it takes almost any species that is common where it hunts. In the breeding season most prey weighs 10 to 40 grams. Larks, pipits, finches, house sparrows, wheatears, thrushes, kinglets and buntings all appear in the diet. Inexperienced young birds of the year are taken most readily of all. Larger prey includes sandpipers, woodpeckers, grouse, ducks and rock doves as heavy as the falcon itself.

Speed and agility do the work, and the bird catches most of its prey in the air. It flies fast and less than 1 metre above the ground, using trees and shrubs as cover. It then tail-chases the bird it has flushed until the chase is won or lost. A pair often hunts together, with one bird driving prey towards its mate. Merlins also follow sharp-shinned hawks and snatch the birds those hunters flush into the open.

In poor conditions about one attack in 20 succeeds, and in good conditions almost half do. The falcon caches food it cannot eat at once. Insects, bats, voles, lemmings, lizards and even amphibians pad the diet outside the breeding season. In Norway a good vole year lifts breeding success well above the usual level. The bird is bold enough to chase cars and trains, and it will rob mist nets set by ornithologists.

Behaviour and social life

The merlin is aggressive out of all proportion to its size. It drives larger raptors out of its airspace, and birdwatchers use that habit to find it. One raptor guide notes merlins harassing birds as large as a golden eagle. Because of that boldness, other meat-eating birds usually leave the merlin alone. Small birds, by contrast, avoid a hunting merlin whenever they can.

Pairs stay together through a breeding season and hold a territory around the nest. Outside the season the bird is usually alone, except at a winter roost. Some merlins in North America have taken to towns so well that they no longer migrate. A first-year male sometimes stays on as a helper at another pair's nest. The falcon appears to perch openly on a post or a low branch between flights.

Communication and senses

The merlin appears to rely on sight above every other sense. It probably has to judge a moving target at speed and only a metre above the ground. A hunting bird probably reads the panic of a flock and picks the bird that flies badly. In the Cayman Islands, bananaquits have died of shock during a merlin attack without being touched.

Calls are chattering and shrill, and they appear to carry furthest around the nest. A pair probably calls while passing food and while driving off an intruder. The merlin also signals with flight, and a dive at a larger raptor may be a message in itself. Falconers appear to judge a merlin's mood from its posture and from how it answers the lure.

Reproduction and life cycle

Breeding usually happens in May and June. Pairs are monogamous for the season, though birds do mate outside the pair. The merlin builds no nest of its own. It takes over an old crow or magpie nest in a stand of conifers, or an old hawk nest. On British moorland the female scrapes a hollow in deep heather instead. Some pairs use a cliff crevice, bare ground or even a building.

The clutch is three to six eggs, and usually four or five. The eggs are rusty brown and average about 40 millimetres by 31.5 mm. Incubation runs 28 to 32 days, and the female does about 90 percent of it. The male hunts through that period and brings food to the nest. Chicks hatch at about 13 grams, covered in pale buff down.

The young fly after about 30 days and depend on their parents for up to four more weeks. More than half of the eggs in a clutch usually hatch, and two-thirds of the chicks fledge. In a year with little food only one chick in three may reach the wing. Merlins are mature at one year old and normally try to breed at once. The oldest wild bird on record reached 12.7 years, and one captive bird was reported at 16.

Predators and threats

Crows and their relatives are the main danger to eggs and nestlings. Peregrine falcons, eagle-owls and goshawks kill adult merlins. Those attacks are uncommon, because the merlin is quick and fights back hard. The nest itself is probably exposed, since the falcon uses whatever another bird built.

Collision with a man-made object is the commonest accidental death, often during a chase. That may account for almost half of all early deaths. Organochlorine pesticides thinned eggshells and broke down immune systems in the 1960s and 1970s. Canadian populations fell hardest, and they recovered after DDT was restricted. Habitat loss on the breeding grounds is the long-term problem, above all on burnt moorland.

Population and conservation

The IUCN Red List rates the merlin as Least Concern. The range is huge, and most countries in it hold hundreds or thousands of birds. Belarus held 250 to 300 pairs, while European Russia was credited with up to 30,000 pairs in 1993. North American numbers have risen sharply in recent decades. European numbers grew until about 2000 and have held steady since.

The species is listed on Appendix II of CITES, so international trade needs an export permit. Britain places the merlin on the Red list and protects it under Schedule 1 of the Wildlife and Countryside Act. Estonia and Portugal list the bird as Vulnerable, and Sweden as Near Threatened. Moorland managed by burning large blocks of heather loses the tall growth that ground nesters need. A mosaic of old and new heather appears to serve the bird far better.

Relationship with humans

The merlin has followed people into towns rather than away from them. Some North American birds now live in cities all year and skip migration. The falcon takes house sparrows and starlings, which are probably drawn to settled ground themselves. Nest sites, not food, are usually what limits a merlin in a settled landscape.

Artists have drawn the bird for centuries. William Lewin figured it in 1789 in his Birds of Great Britain and their Eggs. John James Audubon painted it as Plate 75 of Birds of America under the title Le Petit Caporal. Audubon later admitted the bird he had called Falco temerarius was simply a small male merlin. Some countries still allow merlins to be taken for falconry under licence.

In culture and myth

In medieval European falconry the merlin was a popular and fashionable bird. The Book of Saint Albans, printed in 1486, matched each hawk to a rank of person. Its list gave the gyrfalcon to a king, the peregrine to an earl and the merlin to a lady. The same book praised the merlin for ringing flights after the English skylark. Ringing means climbing in tight circles after prey that tries to out-fly the falcon.

In English folklore the falcon is often confused with the wizard Merlin, and the two names are unrelated. In North American usage the bird was the pigeon hawk well into the twentieth century. In Ojibwe the bird carries the name Bibiigiwizens. In modern falconry writing the merlin is praised for raw power in a very small body.