Northern Saw-whet Owl
(Aegolius acadicus)
Classification
and Range
Saw-whet owls are classified in the order Strigiformes,
which includes typical owls and barn owls. Approximately
160 species of owls are further classified into the family
Strigidae, which includes 26 genera of “typical
owls.” Saw-whet owls belong to one of four species
in the genus Aegolius, or so-called “small forest
owls.” There are just two subspecies of Saw-whet
owls: A. a. acadicus and A. a. brooksi.Saw-whet owls
are one of the most common and widespread of North American
owl species. The breeding range of the northern saw-whet
owl extends from New England and the Eastern Canadian
provinces across the Great Lakes region and southern
Canadian plains into British Columbia. The western part
of their breeding range extends from southern Alaska
down through California, the southwestern states and
into the mountains of Mexico. Their non-breeding range
encompasses most of North America.
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Habitat
Northern saw-whet owls can be found in a variety of forested landscapes throughout
their range including coniferous, deciduous, and even riparian woodlands
in shrub steppe habitats. They prefer riparian habitats for breeding, and
dense cover for roosting. They are only found in urban areas during migration.
These owls rarely live at lower altitudes an appear more frequently at
moderate elevations.
Physical
Characteristics
The saw-whet is one
of the smallest species of owls. It has a large rounded head,
a short tail and a relatively long wingspan. They measure
7-8.5 inches (18-22 cm) in length, with a wingspan of 17-21
inches (23-53 cm). They weigh 2.6-4.6 ounces (75-130 g),
with females larger in length and weight than males.
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Range Map |
Unlike some other owls, this species
does not possess ear tufts, but instead has a prominent facial disk.
Northern saw-whet owls are heavily feathered and feature complex
markings. The upperparts are brown and streaked with white on the
crown and nape. There are white spots on the back, tail and wings.
The facial disk is white above and between the eyes and the rest
is grayish brown with dark brown and white lateral streaks. The underparts
are mostly white with broad brown streaks. Juveniles are dark brown
on the upperparts and face, with a broad white “V” on
their forehead. The breast and belly are lighter brown with few white
markings. The adults have bright yellow eyes.
Life
Span
Life expectancy
in the wild can reach 8 years, but rarely reaches more than
5 years. Most juveniles do not survive into their second year.
Their life expectancy in captivity is unknown, but one captive
owl lived for 16 years.
Diet
In the wild: northern saw-whet owls primarily catch woodland mice, especially
deer mice. They also eat other types of mice, voles, shrews, and juveniles
of small mammals such as chipmunks. They occasionally catch small birds
(kinglets, wrens, sparrows, pygmy owls and others), along with insects
such as grasshoppers and beetles.
At the
zoo: Keepers feed them small mice.
Reproduction
Although generally monogamous, northern saw-whet owls form pairs that last
only through the breeding season. They probably don’t return
to a specific nest site or partner each year. The female or the pair
chooses a nest in abandoned flicker and pileated woodpecker cavities.
They may also nest in manmade nest boxes. Males may attract mates by
singing to them from a suitable nest cavity. Sometime between March
and July, the female will lay a clutch of four to seven eggs (average
is five to six) at two-day intervals. The male brings food to the female,
which incubates the eggs for 27-29 days. The female rarely leaves the
nest during incubation.
After hatching, the female broods the young for at least another 18 days.
After this, she may assist the male with feeding for up to a month thereafter.
If prey is abundant and it is not too late in the breeding season, she
may leave the chicks and the male to find another male and hatch another
brood. The young fledge 4-5 weeks from hatching, and are thought to be
fully independent between 10-13 weeks old. It is thought that they begin
breeding as early as 1 year old.
Life
Cycle
Northern saw-whet owls are solitary and nomadic except during
the breeding season. By day, they commonly roost on lower branches of a
large tree. They often return to the same tree day after day and can be
found by the resulting pile of feces. Migration patterns of the northern
saw-whet owl are quite varied. The patterns range from minor local changes
in location to extensive movement from northern breeding ranges to southern
North America.
Northern saw-whet owls make a number of different sounds including rhythmic
toots, skews, twitters, barks and whining whistles.
Hunting
by Night
The saw-whet owl is nocturnal and is ideally suited for hunting
in darkness. They start hunting shortly after sunset and continue until
just before sunrise. As is the case with most owls, northern saw-whet owls
have large eyes that are well-suited for low light or night vision. They
also have exceptional hearing and are more reliant on it as a sense for
locating their prey. Also like some other owl species, the saw-whet possesses
asymmetrical ear openings in its skull (one opening is located higher than
the other). The asymmetrical layout allows the northern saw-whet owl to
more easily distinguish both vertical and horizontal sound position. Lastly,
its facial disk further amplifies sound.
Saw-whets
are opportunistic hunters that rely on hunting perches, such as branches
and fence posts along forest
edges or other open areas. The
saw-whet captures prey using its strong feet and sharp talons. Each foot
has four toes, and the outer toe of each foot can be rotated in a number
of positions. This allows the northern saw-whet owl to maximize the strength
of its grip on its prey.
A
Pellet a Day
Saw-whet owls often eat only half of a captured prey item at one
sitting. They cache the rest on a branch to eat later. Like other owls,
northern saw-whets typically swallow most of their prey whole. In turn,
their digestive system compresses indigestible parts of prey species (like
bones, feathers and fur) into a small, compact pellet. Saw-whets regurgitate
one 1 inch-long (2.54 cm) pellet a day.
Location
at the Zoo
A female northern saw-whet owl can be seen at the zoo's Raptor Center. Although
it is not tethered outside like the other raptors, it is often held at the
fence by staff or volunteers. Other birds that can be found at the Raptor Center
include the bald eagle, gyrfalcon, Harris's hawk, turkey vulture and spectacled
owl. Additionally, other owls can be seen in the zoo's Temperate Forest bioclimatic
zone: a great gray or spotted owl adjacent to Bug World and a barn owl at the
Family Farm.
Conservation
Connection
Northern saw-whet owls are not an endangered species. They are fairly common
across their range, but their numbers may drop due to development, removal of
nesting snags and hazards encountered in migration. Logging in mature and old-growth
forests also threatens their numbers.
Other species of owls in the family Strigidae are not so fortunate, with at least
12 species listed as endangered. There is an escalation in human-caused changes
in land use, and this affects the habitats and migratory corridors required by
many raptors for survival. The timber and paper product industry removes vast
forests, while industrial emissions pollute water and air resources.
As
human communities expand and agricultural needs increase, they rapidly
convert critical
shoreline and riparian zone habitats. Illegal shooting and trapping
also lower raptor numbers. It’s only a matter of time until more raptor
species may face extinction, unless we protect their habitats.
Humans
need raptors. Here are only a few of the benefits raptors
provide:
- Raptors
help keep animal populations in balance.
- Raptors
consume many animals that humans consider as pests, including mice,
rats and destructive species of insects. This helps to control disease
and damage to crops.
- As
top predators of their food chain, raptors are an indicator species
of the overall health of the ecosystem in which they live.
- Of
equal importance, witnessing wild raptors enriches each of our lives.
Imagine what life would be like if we could no longer hear the haunting
evening call of the owl.
How
You Can Help!
Northern saw-whet owls can be encouraged to nest in disturbed areas by putting
up nest boxes. You can also preserve and provide habitat for breeding and roosting,
even in your own backyard.
Efforts
to save threatened and endangered raptors require cooperation and support
at international, national, regional and individual
levels. You can help in
this cause. Join and become active in Woodland Park Zoo and other conservation
organizations. Recycle forest products. Eliminate or reduce pesticide use.
Support breeding programs for endangered birds of prey at zoos and other
animal care organizations. Let your elected representatives know your
views about
the conservation of migratory birds and their wild habitats.
Contact Woodland Park Zoo at webkeeper@zoo.org to find ways you can
support conservation programs at the zoo or visit our How
You Can Help section.
Sources
and Suggested Reading
Cannings, Richard J. 1993. Northern Saw-whet Owl in: The Birds
of North America Life Histories for the 21st Century, No. 42 (A.
Poole and F. Gill, eds.). American Ornithologists' Union in partnership
with the Academy of Natural Sciences, Philadelphia, PA.
Johnsgard, Paul A. 1988. North American Owls, Biology and Natural History.
Smithsonian Institution Press, Washington D.C., 295 p.
del Hoyo, Josep et al. 1999. Handbook of the Birds of the World,
Volume 5. Lynx Edicions, Barcelona, Spain. 696 p.
Sibley, D.A. 2001. The Sibley Guide to Bird Life & Behavior. Alfred
A. Knopf, Inc., New York, NY. 608 p.
Vanner,
M. 2002. The Encyclopedia of North American Birds. Barnes & Noble,
Inc., New York, NY. 384 p.
de
la Torre, Julio. 1990. Owls: Their Life and Behavior. Crown
Publishers Inc., New York, NY. 214 p.
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