American Kestrel: North America’s Smallest Falcon

The American Kestrel (Falco sparverius) is North America’s smallest falcon and, for many people, the first raptor they ever identify with confidence. It is a robin-sized hunter of open fields and roadsides that hovers over grass, drops onto grasshoppers, and nests in a box nailed to a fence post. It is also, quietly, in trouble: across much of North America its numbers have fallen substantially since the 1960s, and no one can yet explain the decline with certainty. That combination — familiar, approachable, and puzzling — is what makes the kestrel one of the most interesting raptors on the continent.

North America’s Smallest Falcon

A kestrel is small enough to sit comfortably on a wire beside a sparrow, and that is the first clue to its identity. It is not a hawk, not a shrike, and not a songbird, though at a glance it can be mistaken for all three. It is a falcon — a true falcon of the genus Falco — but a tiny one, distinguished from other North American falcons by its size and by its colour. The Merlin is noticeably larger, bulkier, and much darker, and the Peregrine Falcon is in a different size class altogether.

The species ranges from Alaska and Canada all the way to Tierra del Fuego, making it one of the most widespread raptors in the Americas. Several subspecies are recognised, and northern birds tend to be larger and more migratory than tropical ones. Historically it was called the “sparrow hawk” in North America, a name now generally avoided because of confusion with the unrelated Eurasian Sparrowhawk, and it was also sometimes called the “grasshopper hawk” for its taste for large insects.

Identification

The kestrel’s face is its signature. Two bold vertical dark stripes mark the sides of the head against a pale, whitish cheek, and the crown is rufous. The male and female differ enough that a beginner may take them for two species.

In flight the kestrel shows long, pointed wings and a long tail, and it frequently flies with quick, shallow wingbeats punctuated by glides. When perched it bobs its tail expressively, a small behavioural detail that often confirms the identification before the colours resolve.

Hovering, Hunting, and Ultraviolet Vision

The kestrel is one of the most accomplished hovering raptors in North America. It is a wind-hoverer: rather than flapping in place, it prefers to face into a headwind and hold position with minimal effort, scanning the grass below with its head held perfectly steady. When it spots prey it drops in stages — a short fall, a pause, then a final pounce to the ground. It also hunts from perches such as wires, fence posts, and dead branches, and it pursues large flying insects on the wing.

One of the kestrel’s most remarkable adaptations is its ability to see in the ultraviolet part of the spectrum, something the human eye cannot do. Because the urine and droppings of voles and other small rodents reflect ultraviolet light, the theory runs that hunting kestrels can follow these trails through vegetation, effectively reading the runways of their prey. It is a striking example of how a raptor’s senses are tuned to its habitat.

Diet

Unusually among falcons, the American Kestrel leans heavily on invertebrates, especially in summer. Its menu typically includes:

• Insects: grasshoppers, crickets, beetles, dragonflies, cicadas, and moths — often the bulk of summer prey.
• Small mammals: voles, mice, and shrews, which become more important in winter and in northern latitudes.
• Small birds: sparrows, finches, and other small passerines, taken less often than by larger falcons.
• Reptiles and amphibians: lizards, snakes, and frogs, chiefly in warmer parts of the range.

This eclectic diet is one reason the kestrel copes with a wide range of habitats — and one reason it is sensitive to anything that reduces insect abundance.

Nest Boxes and Breeding

Kestrels do not build nests. They are secondary cavity nesters, meaning they depend on holes made by others: natural tree cavities, old woodpecker holes, crevices in buildings, and, happily for conservationists, purpose-built nest boxes. A kestrel box mounted on a pole or tree in open country is one of the most reliable ways to attract a breeding pair, and box programmes have become a mainstay of kestrel conservation.

• Clutch: typically four to five eggs, sometimes up to six or seven.
• Incubation: about 29–31 days, mainly by the female while the male brings food.
• Fledging: around 28–31 days, with young birds dependent on their parents for a further two to three weeks.
• Competition for cavities: European Starlings and other hole-nesters often take over suitable cavities, and the loss of nesting holes is a real pressure on kestrel numbers.

The Declining-Numbers Puzzle

The American Kestrel is still a common bird, and globally it is assessed as Least Concern. But long-running survey data in North America show a broad and substantial decline since the mid-1960s — on the order of half the population over roughly the past fifty years, with steeper losses in some regions than others. The troubling part is that no single cause has been proven. The leading candidates are:

• Loss of nesting cavities — fewer old trees, fence posts, and safe holes in a tidier landscape.
• Reduced insect prey — pesticides, including neonicotinoids, cut the kestrel’s summer food supply.
• Predation — recovering populations of Cooper’s Hawks and other raptors may take more kestrels than before.
• Habitat change — conversion of grassland and pasture to intensive agriculture reduces both prey and hunting ground.
• Climate and disease — shifting weather and pathogens such as West Nile virus are plausible additional pressures.

Because several of these overlap, the honest answer to “why are kestrels declining?” is that we do not yet know. It may well be a combination. The broader context for declining raptors is discussed in endangered raptors, and the most useful thing an individual can do is straightforward: put up a nest box in suitable habitat. See how to help save birds of prey for practical steps.

Frequently Asked Questions

Is the American Kestrel really a falcon?

Yes. Despite its small size it is a true falcon (Falco sparverius), related to the Merlin and the Peregrine Falcon. Its pointed wings, compact body, and fast direct flight are all characteristic of the family. See the falcons complete guide for the family overview.

American Kestrel or Merlin — how do I tell them apart?

Size and colour do most of the work. The kestrel is smaller and much more colourful, with a rufous back and tail, a blue-grey wing on males, and two bold dark face stripes. The Merlin is bigger, darker, and more uniformly brown or grey with heavy streaking.

Do American Kestrels migrate?

Northern birds do. Kestrels breeding in Canada and the northern United States commonly move south for winter, while birds in warmer regions may be resident year-round. Migration is broad-fronted rather than concentrated at a few watchpoints.

What do American Kestrels eat?

Mainly insects such as grasshoppers and beetles in summer, with small mammals like voles and mice becoming more important in winter. They also take small birds, lizards, snakes, and frogs.

Will kestrels use a nest box?

Readily — it is one of the easiest ways to help them. Mount a box on a pole or tree in open grassland or farmland, well away from trees that might hide predators, and kestrels will often investigate within a season.

Why are American Kestrel numbers dropping?

No single cause is confirmed. Loss of nesting cavities, reduced insect prey, increased predation by recovering raptors, and habitat change are all plausible and may act together. This is why nest-box programmes and prey-friendly habitat are the current focus of kestrel conservation.

Learn to tell it from its larger relative in the Merlin, or explore the family in the falcons complete guide.