October 20 – Eye On The Sparrow Hawk

Today’s factismal: The American Kestrel is the smallest and most common raptor in North America.

If you ask the typical seven year old “What is a raptor?”, they will probably tell you that it is a kind of dinosaur. They are right (sort of), but they are also wrong (sort of). That’s because biologists use the word “raptor” to refer to any bird that has good eyesight for finding prey, strong talons for catching prey, and a hooked beak for eating prey; as you might guess, the other term that biologists use for raptors is “birds of prey”. (But the biological raptors are related to the dinosaur raptors, so the seven year old wasn’t completely wrong.) And one of the coolest raptors is also one of the most common: the American Kestrel, also known as the sparrow hawk or Falco sparverius (“falcon of sparrows” – refers to the hooked {falconate} beak).

An American Kestrel (or sparrow hawk) in flight (Image courtesy USFWS)

An American Kestrel (or sparrow hawk) in flight
(Image courtesy USFWS)

Interestingly, the sparrow hawk rarely eats sparrows, simply because they are almost as large as it is! Instead, this kestrel prefers to eat grasshoppers, mice, and small lizards, which are much easier to catch and provide a filling meal to the foot-long sparrow hawk. Because their prey lives in a variety of habitats, so do American kestrels; they can be found in deserts, meadows, prairies, and even cities. About all they require is something to perch on while they look for prey, open spaces to catch the prey in, and empty cavities to put their nests in. Thanks to their adaptability, they are found from Alaska (where they can spend the summer) to Tierra del Fuego (where they pasa el verano). An estimated 2.4 million American kestrels live in North America in the summer, dropping to about 480,000 in the winter. However, there are large uncertainties in both numbers as the American kestrel hasn’t been extensively studied.

A young American kestrel (Image courtesy USFWS)

A young American kestrel
(Image courtesy USFWS)

What is known about this bird is fascinating. They range in size from as big as your fist to as large as a Harry Potter novel (and just as entertaining). Like all birds, they are light for their size; a fully grown American kestrel won’t weigh much more than 4 oz. They can live for about twelve years (though five years is more typical) and are sexually mature after just one year. They pair bond, frequently for life, and often reuse the same nest from year to year. The female will lay up to seven eggs, with one egg each day. After a month of incubation (during which the female does most of the work), the chicks hatch and immediately start arguing over who gets the worms. The chicks grow to full weight in two weeks and just one month after being hatched, they leave the nest.

An adult American kestrel (Image courtesy USFWS)

An adult American kestrel
(Image courtesy USFWS)

Despite their apparent fecundity, the American kestrel population is declining. Biologists aren’t sure quite why this is happening. It may be due to reductions in their habitat, or a subtle reaction to new pesticides, or changes in climate leading to changes in the number of prey. The only way for biologists to understand the change is for them to get data – and that’s where you come in. The American Kestrel Partnership is looking for reports of sparrow hawk sightings and for people willing to build and observe kestrel nestboxes. If you’re game, then head over to their site to learn how you can participate:
http://kestrel.peregrinefund.org/

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