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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.

 

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.

Northern Saw-whet Owl
Figure 1 - Northern Saw-whet Owl

 

Northern Saw-whet Owl
Figure 2 - Northern Saw-whet Owl

 

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.

Northern Saw-whet Owl
Figure 3 - Northern Saw-whet Owl

 

Northern Saw-whet Owl
Figure 4 - Northern Saw-whet Owl

 

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.

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.

Northern Saw-whet Owl feet
Figure 5 - Northern Saw-whet Owl feet

 

Northern Saw-whet Owl wing
Figure 6 - Northern Saw-whet Owl wing

 

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!

 

Northern Saw-whet Owl under wing
Figure 7 - Northern Saw-whet Owl under wing

 

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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