Merlin

Description

The merlin is 24–33 cm (9.4–13.0 in) long with a 50–73 cm (20–29 in) wingspan. Compared with most other small falcons, 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). 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 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 the tarsi measure 3.7 cm (1.5 in). 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.

Behaviour

Merlins inhabit fairly open country, such as willow or birch scrub or shrubland, but also taiga forest, parks, grassland such as steppe and prairies, or moorland. They are not very habitat-specific and can be found from sea level to the treeline. In general, they prefer a mix of low- and medium-height vegetation with some trees and avoid dense forests, as well as treeless arid regions. During migration, however, they use almost any habitat. Most populations are migratory, wintering in warmer regions. Northern European birds move to southern Europe and North Africa, and North American populations to the southern United States to northern South America. In the milder maritime parts of its breeding range, such as Great Britain, the Pacific Northwest, and western Iceland, as well as in Central Asia, it merely deserts higher ground and moves 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 southern Russia 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 in Ohio, just south of the breeding range, F. c. columbarius is typically recorded as a southbound migrant as late as September/October. In Europe, merlins roost communally in winter, often with hen 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. They actually capture most prey in the air and "tail-chase" startled birds. Throughout their native range, merlins are some of the most able aerial predators of small to midsized birds, more versatile than hobbies (which prefer to attack in midair) and the nimbler sparrowhawks (which usually go for birds resting or sleeping in dense growth). Breeding pairs frequently hunt cooperatively, with one bird flushing the prey toward its mate. The merlin readily takes prey that is flushed by other causes and can, for example, be seen tagging along sharp-shinned hawks (Accipiter striatus) to catch birds that escape from this ambush predator into the open air. It is quite unafraid, so readily attacks any prey that moves conspicuously. Merlins have even been observed trying to "catch" automobiles and trains and to feed on captive birds such as those snared in the mist nets used by ornithologists. Even under adverse conditions, one in 20 targets is usually caught, and under good conditions, almost half of attacks are successful. Sometimes, merlins cache food to eat it later. In particular during the breeding season, most of the prey are smallish birds weighing 10–40 g (0.35–1.41 oz). Almost any such species is taken, with local preferences for whatever is most abundant—be it larks (Alaudidae), pipits (Anthus), finches (Fringillidae), house sparrows (Passer domesticus), other Old World sparrows (Passeridae), northern wheatears (Oenanthe oenanthe), thrushes (Turdus), kinglets (Regulidae) or buntings (Emberiza)—and inexperienced yearlings always a favorite. Smaller birds generally avoid a hunting merlin if possible. In the Cayman Islands (where it only occurs in winter), bananaquits were noted to die of an apparent heart attack or stroke, without being physically harmed, when a merlin went at them and they could not escape. Larger birds (e.g. sandpipers, flickers, other woodpeckers, ptarmigan, other grouse, ducks and even rock doves as heavy as the merlin itself) and other animals—insects (especially dragonflies, moths, grasshoppers, butterflies, and beetles), small mammals, (especially bats, shrews, rabbits, voles, lemmings and other small rodents) reptiles (such as lizards and snakes) and amphibians—complement its diet. These are more important outside the breeding season, when they can make up a considerable part of the merlin's diet. For example in Norway, though, while small birds are certainly the breeding merlin's staple food, exceptional breeding success seems to require an abundance of Microtus voles. Corvids are the primary threat to eggs and nestlings. Adult merlins may be preyed on by larger raptors, especially peregrine falcons (F. peregrinus), eagle-owls (e.g., great horned owl, Bubo virginianus), and larger Accipiter hawks (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, "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)".

Adapted from Merlin (bird) on Wikipedia, used under CC BY-SA 4.0.