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Northern Saw-whet Owl
(Aegolius acadicus)
Banded 2 November, 2002
Bloomington, Indiana
General Information
The Northern Saw-whet Owl is one of 19 species of owls that occur in
North America, and the smallest owl that occurs in eastern North America.
Their name derives from a particular early spring courtship note, uttered in
groups of threes, sounds like a file rasping on a large mill saw blade. It
has been described as sounding like skreigh-aw, skreigh-aw skreigh-aw. The
more well known call is an endless, monotonous succession of
too-too-too-too-too notes repeated 80 to 100 times a minute.
The Northern Saw-whet Owl is a bird of coniferous and deciduous
woodlands. Many species of owls are circumpolar in distribution, but this
species is found only in North and parts of Central America.
This owl is highly migratory, and some winter well into the central parts
of the USA. They are tame, and often allow humans to approach closely.
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The Northern Saw-whet Owl is
about 8 inches long with a wingspan of 17-20 inches. It weighs about 3
ounces. Sexes are similar, but the female is a bit larger than the male.
They are strictly nocturnal, and although large numbers occur in their
range, they are mostly overlooked and considered uncommon.
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Figure 1 - Northern Saw-whet Owl
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Figure 2 - Northern Saw-whet Owl
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The facial disc of the owl has
a whitish “V” pattern with the base starting at the bill. The eyes face
forward giving the owl binocular vision and good depth perception. The
eyeballs are fixed in their sockets, so to look around, the owl must turn
its head. Owls are famous for their ability to rotate their head completely
around to look behind themselves. |
The dark beak is small and
hooked, and well adapted to feed on their preferred diet of insects, mice,
small rats, chipmunks, shrews, red-squirrels, bats, sparrows, juncos,
kinglets, wrens and warblers.
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Figure 3 - Northern Saw-whet Owl
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Figure 4 - Northern Saw-whet Owl
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The yellow iris is typical of
the owls. Here the color of the iris is compared to various yellow color
swatches to determine the particular shade of yellow. Data gained from these
studies may prove useful to determine age.
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The feet of this owl are
feathered down to the toe nails. There are four toes. Two face forward, and
one faces to the rear. The fourth toe can be extended either forward for
perching or backward for catching and holding prey. |
Figure 5 - Northern Saw-whet Owl feet
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Figure 6 - Northern Saw-whet Owl wing
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The wing is brown with white
markings. The leading edge of each wing has a special comb-like structure
that reduces the noise that the wing would otherwise make as it cuts through
the air. This allows the bird to fly silently, and listen for and locate the
faint sounds of mice and other prey moving about in total darkness. |
The under wing feathers glow
under ultraviolet light. This characteristic is useful to study the molt
patterns of the wing feathers, and suggests some interesting possibilities.
Can these owls see in the ultraviolet light (UV) part of the spectrum?
Although these birds are virtually invisible to us in the dark, could it be
possible that they can observe each other in the UV part of the spectrum,
and perhaps even determine their age and sex from the UV patterns of the
wing? Studies have already shown that other birds and animals use the UV
part of the spectrum. This sounds like a fruitful topic for
a research project! |
Figure 7 - Northern Saw-whet Owl under wing
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Nesting Behavior
Saw-whet Owls breed across the southern parts of Canada, and at higher
elevations in eastern USA, western USA and Mexico. The nest is located in an
unlined cavity from 14 to 60 feet above the ground. They will also use
artificial nest-boxes. Nesting begins in mid-March. From 3 to 6 eggs are
laid at 1 to 3 day intervals, are incubated by the female. The eggs hatch in
about 4 weeks, usually in intervals, so the young birds will be at different
stages of development. The male brings food to the nest for the first 3
weeks, and the young fledge in another 4 to 5 weeks.
Banding Recoveries
According the web page of the Bird Banding Lab, 74,346 Saw-whet Owls were
banded between 1955 and 2000.
Banding studies show that Saw-whet Owls are highly migratory, and can
cover a distance of 140 miles in a matter of hours. The have lived up to 17
years in captivity. Intensive studies are now underway to monitor numbers
and timing of movements of the fall migration patterns of these owls. What
has been learned is that there are many more of these owls around and moving
through their migration range than expected.
If you should recover a banded bird, please report the band number to the
Bird Banding Lab by calling 1-800-327-BAND.
Economic Importance and Conservation Status
Populations of Saw-whet Owls are apparently doing well. One of the first
reported indications that these owls are more common than expected, and that
they migrate in large numbers, occurred in 1903 when a ship captain on Lake
Erie reported that a large number of these owls were seen at night over the
lake, and many landed on the ship. In another incident in 1906, a large
number of birds were killed in a storm while crossing Lake Huron. Among the
thousands of dead birds on the lake were a number of Saw-whet Owls.
Recent banding studies are revealing that hundreds of these birds are
passing through in areas where only a few were ever seen in previous years.
These gentle, attractive, and trusting birds are worthy of conservation
efforts. Although seldom seen, they create a sense of wonder and delight
when they are encountered. It is just nice to know that we share our world
with delightful and attractive creatures such as these.
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All images are courtesy of CWBO. All image copyrights are owned by CWBO.
Any use of these images must have permission of CWBO. |
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