Merlin (bird) - Ecology

Ecology

Merlins inhabit fairly open country, such as willow or birch scrub, 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 will utilize almost any habitat.

Most of its populations are migratory, wintering in warmer regions. Northern European birds move to southern Europe and North Africa, and North American populations to the southern USA 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 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 USA, 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 e.g. 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 will roost communally in winter, often with Hen Harriers (Circus cyaneus). In North America, communal roosting is rare, and Merlins are well known for fiercely attacking any birds of prey that they encounter, even adult eagles.

Merlins rely on speed and agility to hunt their prey. They often hunt by flying fast and low, typically less than 1 metre 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 larger hobbies (which prefer to attack in mid-air) and the more nimble sparrowhawks (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.

The Merlin will readily take 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, and will readily attack anything 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 every other attack will be 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 (0.35–1.4 oz). Almost any such species will be taken, with local preferences for whatever is most abundant—be it larks (Alaudidae), pipits (Anthus) or House Sparrows (Passer domesticus)—and inexperienced yearlings always a favorite. Smaller birds will generally avoid a hunting Merlin if possible. Even 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 and even Rock Pigeons as heavy as the Merlin itself) and other animals—insects (especially dragonflies and moths), small mammals (especially bats and voles) and reptiles—complement its diet. These are more important outside the breeding season, when they can make up a considerable part of the Merlin's diet. But for example in Norway, 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.