Both the Kestrel (Falco tinnunculus) of the United Kingdom and the American Kestrel (Falco sparverius) are widespread raptors of the Falco genus. These small birds of prey are the best known of about fifteen similar species that occur on every continent except Antarctica.
This genus contains many other celebrated masters of the sky, such as the Peregrine Falcon, the world's fastest bird. Kestrels might not be quite as fast as some other falcons, but they are well-known for their remarkable ability to hover.
So how do Kestrels hover, and how does this impressive ability benefit them?
Kestrels hover by facing the wind and making controlled movements of their wings and tails to keep them stationary relative to the ground. These birds can remain seemingly motionless in a breeze but will flap their wings quite rapidly to achieve the same result on a calmer day. This hovering flight allows them to carefully scan the ground below, waiting for a rodent to scurry into view.
The Kestrel has long been admired for its ability to hover while hunting. This behaviour is typically known as windhovering and is also employed by some other birds that hunt from above.
The Kestrel was known traditionally as the ‘windhover’ and admiringly described by the 19th-century poet Gerard Manley Hopkins in a poem by the same name.
This article unpacks the hovering behaviour of the Kestrel, a common and widespread British raptor with a keen eye and remarkable coordination.
Male Common Kestrel hovering
Hovering to remain stationary is a balancing act. Kestrels hover by flying into the wind at the same speed as the air is flowing - allowing them to stay in place relative to the ground below. This simple explanation describes how they remain in the same position on a horizontal axis but doesn’t quite explain why they do not fall to the ground.
Kestrels need to harness or create lift to counteract the ever-present pull of gravity. They can hover in place without flapping their wings by using the energy of the wind. By angling their wings upwards, Kestrels can stay aloft just like a kite on a string. Of course, wind flow is not perfectly constant, so the birds must use complex and rapidly changing movements to steady themselves.
Kestrels flap their wings and move their broad tails to maintain their balance. To start hovering, Kestrels can spread their tail feathers and angle them downwards, effectively putting on the brakes to get them started. Their tail is particularly useful for other stabilizing movements as it can be twisted to either side, opened or closed, and lowered as necessary.
Kestrels hover to improve their chance of spotting prey on the ground below them. To do this, their head must remain perfectly still so their vision will not be blurred.
Keep reading to learn how Kestrels achieve this seemingly impossible task.
Kestrels use complex and rapid changing movements to steady themselves
Hovering Kestrels have the remarkable ability to keep their heads still in flight. Like other birds, they can’t move their eyes a great deal and must shift their entire head to steady their vision. Kestrels use the many vertebrae and muscles in their necks to keep their eyes focused. This behaviour is commonly seen as head-bobbing in other bird species.
Kestrels can hover when there is no wind. This ability is shown by a captive American Kestrel trained to hover indoors for educational purposes. The effect is far less graceful and cannot be maintained for quite as long, however.
Remaining in position relative to the ground requires far more energy in still conditions. In this case, the Kestrel must flap its wings constantly to counter the force of gravity.
The natural flapping action of the Kestrel propels it forwards on a horizontal plane, so the birds must change the angle of their wings or the path of their downstroke to keep them in one place.
Female Kestrel hovering in the sky, looking for prey
Kestrels prey on small ground animals like voles, which they hunt from above. These birds hover to get a better view of the ground below and the time to spot their quarry, wait for the perfect moment, and then to swoop down to grasp the unsuspecting animal with their sharp talons.
Kestrels do not have to hover to find their prey. They will also hunt from a perch such as a telephone pole or large tree that provides a good vantage point. Hovering allows them to find their prey in open country like moorlands where no such perches are available.
This hunting strategy can be viewed as a high-cost but high-reward technique because it allows the birds to hunt over the best areas rather than the immediate vicinity of a perch.
Kestrel diving for prey
Kestrels hover when they are hunting. Birdwatchers can spot these diurnal birds hovering at practically any time of day. They windhover with virtually no wing flapping when there is good air movement, but they have to flap their wings much faster in still conditions.
Kestrels often hover for up to half a minute, although they can maintain their position for over a minute in certain conditions. They windhover for longer periods where there is a comfortable headwind. This air movement provides the energy needed to keep them aloft.
When searching for prey, Kestrels often glide forward for a short distance before continuing to hover in a nearby area. These birds tend to spend more time and energy hovering over a productive spot and spend shorter periods hovering over untested hunting grounds.
Kestrels can hover up to half a minute, but when conditions permit, it can be over a minute
Kestrels fledge the nest about a month after hatching. Their first flights are not exactly graceful, but practice makes perfect. Kestrels become accomplished perch hunters within a few weeks of leaving the nest, although mastering hovering probably takes some time longer.
Hovering is a complex form of flight that probably takes much learning. The behaviour is common among Kestrel species across the globe, however, so it is most likely to be at least partly instinctive.
Common Kestrel hovering high in the sky
Scientists call this type of locomotion hovering flight or windhovering.
When it comes to Kestrel flight, hovering can be broken down into the following two categories.
Hanging flight is the relatively stable windhovering flight where Kestrels can stay aloft without flapping their wings. This technique requires stronger winds and uses just a third of the energy that flapping does.
Kestrels can hover in low wind speeds, although this requires much more effort to maintain lift. This type of hovering is called continuous flapping.
Kestrels are famous for their hovering abilities, but they are not the only birds capable of this feat. In fact, most birds can hover for brief periods, often just before landing. Many birds hover in much the same way as Kestrels and for similar reasons.
Let’s take a look at a few other examples of hovering birds.
Various species of terns hunt over the UK’s freshwater bodies and coastline. These agile fish hunters frequently hover above the water before diving in to catch their prey.
Barn owls tend to hunt after dark, so few birdwatchers get to see them hovering. Nevertheless, these expert rodent hunters will hover briefly before swooping in for the kill.
The Buzzard can hover while scanning the ground below for prey. They are much bulkier than Kestrels and are more likely to hover in stronger winds.
Barn Owl hovering, before diving to catch prey
Kestrels might be expert hovering birds, but they are not nearly as agile as Hummingbirds. These tiny acrobats are capable of precision hovering and backwards flight as they move from flower to flower and hunt for insects.
The White-tailed Kite is another American hovering bird that hunts from above. These conspicuous rodent-hunting raptors also hunt from perches.
The Belted Kingfisher is a widespread North American bird that feeds on fish and other aquatic animals. These birds often hover above the water before diving in to catch their prey.
Close up of a White-tailed Kite hovering
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