Vail Daily column: Curious Nature: Take a closer look to identify a kestrel in the Vail Valley
March 10, 2013
The American kestrel is our smallest and most common raptor here in North America. As a member of the genus falco, they are close relatives of merlins, prairie falcons and peregrine falcons. Kestrels are sometimes colloquially referred to as “sparrowhawks,” not because of their habit of preying on song birds (which they do) but because their small size often causes people to confuse them for songbirds. Many readers in Eagle County likely see kestrels much more frequently than they would think but do not acknowledge them for what they are because of their small silhouette. If you aspire to spot a kestrel in the near future, begin by taking a closer look at birds you see perched on fence posts and wires along roads and at the edges of fields. You may also try to listen for their distinctive “krill, krill, krill” call as they are some of the most vocal predatory birds in Colorado.
In spite of their small size (7-8 inches long), kestrels have some advantages that have allowed them to become successfully established across the continent, from central Alaska to central Mexico. Their greatest advantage is their varied diet. While kestrels are known to prey on other small birds, they also take advantage of a prey source that many larger raptors ignore: insects. Kestrels can often be seen zipping over fields and streams in the summer, snatching insects right out of the air. When insects are less numerous or other prey sources are easier to find, kestrels will also feed on small mammals and lizards.
Kestrels are sexually dimorphic, meaning the males and females look different. Both sexes sport rust-colored backs with horizontal tiger stripes, but the wings of the smaller males are adorned with slate blue trim and a solid orange tail with a black tip, while the female’s tiger stripes extend down the length of her tail. Both sexes share a dark vertical stripe under their eyes. This stripe is common among North American falcons, including peregrine falcons and merlins, and serves the same purpose that eye black does for outfielders in baseball. This dark stripe absorbs sunlight, rather than reflecting it, and helps reduce glare into the bird’s eyes. This feature is very important for birds of prey that rely heavily on their eyesight to find and capture prey.
If you have an interest in kestrels and might like to see them more regularly, you may be excited to learn that these woodpecker-sized birds are cavity nesters who will readily occupy a nest box if it is located in a suitable habitat. If your yard abuts a grassy field or meadow, then you might try placing a nest box outside this spring to attract some new avian neighbors. They might even help eliminate some pesky bugs! If you do not live close to an open space that kestrels might like to call home, then do not fear! You can watch nesting kestrels on camera in the spring by visiting http://www.allabout
birds.org. There you will find a 24-hour webcam with a view inside a kestrel nest box. Last year, all five hatchlings fledged and successfully flew away from the nest when they were large enough.
Pete Wadden is a field science educator at Walking Mountains Science Center. Watch out for him in roundabouts in Avon as he tends to get distracted by birds overhead and may swerve into your lane.