Central Wisconsin Kestrel Research
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Kestrel Biology

There are 6 falco species in North America: American Kestrel, Aplomado Falcon, Prairie Falcon, Peregrine Falcon and Gyrfalcon. The American Kestrel is the smallest and most numerous of all North American falcons. Its scientific name, Falco sparverius, hold the Latin meaning, "falcon of the sparrows." Formally known as the sparrow hawk, the American Kestrel generally feeds on small mammals and insects. One exception to this appears to be when kestrel populations live in urban areas. New York City supports a healthy, breeding population of kestrels, where they live on busy city streets in building cornices, and feed primarily on small birds. The rural kestrel typically hunts while perched on utility wires, fence posts, or from the tops of trees. They can also be seen hovering over open areas, searching for prey — hovering takes about 4 times more energy than level flight. The American Kestrel can also be seen bobbing its head up and down. This motion allows the raptor to see an object from many different angles and judge its distance.


Eurasian Kestrels are able to locate voles (small mouse-like rodents) by being able to see their urine trails, which reflect ultraviolet light, visible to the kestrel's eyes. It is quite possible that the closely related and ecologically similar American Kestrel can do the same.


female
male


The male American Kestrel has blue gray wings and an unbarred tail except for a black subterminal band. The female has rufous colored wings barred with black and a tail barred with numerous black bands. The American Kestrel has three vertical black facial stripes and is about the size of a blue jay. American Kestrels have two black spots on the back of their heads called ocelli. These may act as false eyes — to deceive an enemy or thief into thinking that the falcon is looking right at them so the element of surprise is gone.


The female kestrel lays 4-6 eggs, 1 every other day. She typically begins incubation upon laying the penultimate egg. The incubation period is approximately 30 days and the nestlings fledge in 28-31 days. They are dependent on their parents for another 12-14 days. Up to 75% of the young may die during their first year. Mortality rate drops to perhaps 10-20% per year as young falcons fine-tune their survival skills.


American Kestrels prefer open and partly open areas with scattered trees. They are a secondary cavity nester and are the only North American falcon or hawk to nest in cavities. They use woodpecker holes, natural cavities in trees, crevices in rocks, openings in buildings and nest boxes.


Data from hawk migration watchsites, Christmas Bird counts and annual Breeding Bird Surveys seem to indicate that American Kestrel populations have declined substantially, especially in the northeastern parts of the United States. Kestrel numbers in Central Wisconsin appear to be stable.


Even though the American Kestrel has been studied in great detail, additional information will improve our understanding of this raptor. Research from nest box monitoring programs may reveal important information about what might be influencing downward trends.