Friday, October 12, 2012

American Kestrel

Donald Stock 2012                                        
This female American kestrel was spotted frequently hunting in the grassy meadows of the Grange Insurance Audubon Center before she was captured in our mistnet in August. American kestrels are sexually dimorphic, meaning the males and females look different. Males have blue-gray on their wings and a rufous-red tail with one black subterminal band, while females are duller, with brown wings and multiple bars on their tail. We aged this bird as a hatch year using the terminal band on her tail.
Kestrels are the smallest falcon in North American, and are related to the peregrine falcon and merlin, both of which have also been sighted at the Grange Insurance Audubon Center!  Sometimes called sparrow hawks because of their small size, American kestrel’s scientific name, Falco sparverius, means “falcon of the sparrows”. It is very common to see kestrels on a high perch, such as utility wires, tall isolated trees or fence posts, scouting for their prey. The majority of their diet consists of insects (love those grasshoppers!) and small mammals, but urban kestrels have been shown to have a diet consisting primarily of small birds.

Kestrels often bob their heads, which allows them to estimate distance.  Their large eyes sit forward on their head, which allows them to have great depth perception. Their eyes also have a high density of cone receptors, enabling the bird to see detail from great distances! One last awesome fact about their eyesight! They can see in the UV spectrum, which allows them to see the urine trails of the small mammals they are hunting as they hover over a field. COOL!  

Donald Stock 2012                                                                         

American kestrel populations declined in the early and mid-1900s in many parts of North America as a result of a loss in nesting habitat. American kestrels are the only North American falcon or hawk to nest in cavities. They are a secondary cavity nester, which means they do not excavate their own nest, but rather use woodpecker holes, natural cavities, and crevices in rocks. As human population increased, crop fields and urbanized areas replaced suitable nesting habitat. Tree-lined field borders and fencerows were cleared, as were dead standing trees (snags). Luckily, kestrels take readily to nest boxes, and ongoing management practices of placing nest boxes on road signs along highways and in other areas of suitable kestrel habitat are helping their populations to recover.
What you can do:  If you have suitable kestrel habitat on your property, you too can aid this bird species by maintaining natural nesting options such as retained snags, or by providing artificial cavities in the form of nest boxes!

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