Kessie is a female American Kestrel (Falco sparverius) who came
to us as an adult in June of 2000 from Moscow, Idaho with a malaligned,
partially healed fracture of the left humerus. Although she can no
longer fly, Kessie loves sitting on her perch and being admired at
presentations!
American Kestrels are the smallest falcon in North America (and the second
smallest in the world – the smallest is the Pygmy falcon (Polihierax
semitorquatus) found in Africa. There are 5 North American falcons
(going from largest to smallest); the Gyrfalcon (Falco rusticolus),
the Peregrine falcon (Falco peregrinus), the Prairie Falcon (Falco
mexicanus), the Merlin (Falco columbarius), and the American
kestrel.
Kestrels are somewhat unique in that they are sexually dimorphic in color.
The males have blue-grey down their wings, a spotted chest, and one thick
black band across the end of their tail (called a sub-terminal band).
Females are brown on their backs and wings, have vertical dashes on their
chests and have many stripes across their tail. This makes sex determination
very easy - with most other raptors, DNA testing is required.
Kestrels, like all other falcons, have distinct physical features
that are not found in other raptors. These include; the falcon’s tooth,
malar stripes, distinctly pointy wings, and nasal tubercles. The
falcon’s tooth is a small projection in the upper beak, just behind the
tip, that fits neatly into their prey’s vertebrae making it easy to snap
and quickly kill their prey. A corresponding notch in the lower beak
complements the "tooth". Long, pointy and narrow wings enable them to
fly at high speeds. Kestrels in a stoop dive (a near vertical dive) can
reach speeds of up to 60mph. Nasal tubercles are small bones found in
the nose that allow falcons to breathe easier during high speed diving.
Since kestrels are diurnal (hunting during the day), the dark malar
stripes on the face help reduce glare from the sun.
Kestrels are found throughout North America and much of South America,
living in grasslands, semi-open forests, and urban and suburban areas.
They like clear prairie lands to hunt and a few scattered trees or high
places for them to nest and perch. They can be found quite frequently
perched on power lines and you can identify them by their head and tail
bobbing, which is a territorial gesture. Kestrels nest in cavities
– including old abandoned nests of other birds, nest boxes, small rock
crevices, and even holes in the side of a building.
A large portion of the diet of an American Kestrel is grasshoppers and
other large insects. However, they are opportunistic and will also commonly
eat small rodents, birds, bats, or small reptiles. They have been reported
taking down even larger prey like squirrels! Kestrels are often seen
hovering in place over a field, searching for prey. They are able to use
their wings and tail to balance in one place while scanning the ground with
their excellent eyesight. Their vision is thought to be between 8 and 12
times sharper than ours. To put that in perspective, tack a piece of paper
with writing on it onto a wall and walk as far from it as you can while
still being able to read the words. A kestrel would be able to go 12 times
farther away, and still be able to read it! This is not because they can
“zoom in” with their eyes, but simply because their vision is much much
sharper. Kestrels can also see in the ultraviolet light range, allowing them
to track down areas with large quantities of rodent urine, which reflects UV
light.
