BioKIDS home

Kids' Inquiry of Diverse Species

northern saw-whet owl

Aegolius acadicus

What do they look like?

Northern saw-whet owls are the smallest owls in eastern North America. Males weigh only 75 g, which is about the same as an American robin. Females weigh a little more, about 100g. Males are 18 to 20 cm long and females are 20 to 21.5 cm long. Adults have a wingspan of 45 to 60 cm.

Northern saw-whet owls have a reddish-brown body with white streaks on the belly. They also have dark-colored bills, big yellow eyes, feathered legs and feet and a tail with three stripes. They have large, round reddish-brown heads and a flat grayish area around their eyes. Their neck is speckled with white. The speckles and stripes in the feathers of northern saw-whet owls helps to camouflage them when they are roosting and hunting.

Male and female saw-whet owls look similar, but are different in size. Females are slightly larger than males. Young saw-whet owls are chocolate-brown large white spots above their bills and over their eyes. (Cannings, 1993; Government of Alberta, 2000; Long, 1998; The Raptor Center, 2000)

  • Sexual Dimorphism
  • female larger
  • Range mass
    65 to 110 g
    2.29 to 3.88 oz
  • Range length
    18 to 21.5 cm
    7.09 to 8.46 in
  • Range wingspan
    45 to 60 cm
    17.72 to 23.62 in
  • Average basal metabolic rate
    0.654 W
    AnAge

Where do they live?

Northern saw-whet owls are found only in North America. Their breeding range includes southern Alaska, southern Canada, most of the United States and some high elevation sites in central Mexico. (Bisbee, 1998; Cannings, 1993; Long, 1998)

What kind of habitat do they need?

Northern saw-whet owls live in woodlands. They can be found in coniferous forests, deciduous forests and mixed forests. During migration and winter, saw-whet owls can be found in many different habitats. They can be found at low elevations and at high elevations. They may be found in rural or even suburban environments. They seem to be able to live in nearly any habitat as long as it has perches for hunting and dense vegetation for roosting. (Cannings, 1993; Long, 1998; The Raptor Center, 2000; Tufts, 1986)

  • These animals are found in the following types of habitat
  • temperate

How do they reproduce?

Northern saw-whet owls are usually monogamous. However, when a lot of food is available, they can be polygynous. Females may be able to raise two broods in a summer by leaving the male and the chicks of the first brood early and finding another male to mate with. Breeding pairs do not stay together for more than one summer.

Male northern saw-whet owls establish a territory and begin trying to attract females in late winter or early spring. Males advertise to females by calling at them. If the female is interested in the male, she may call back to him. The male and female of a pair sometimes preen each other’s feathers. This is called allopreening. It may help the pair to build a pair bond. (Cannings, 1993)

Northern saw-whet owls breed between March and July. Males begin calling in late winter and early spring to try to attract a female. Once a male and female for a pair, the female chooses a nest site. Northern saw-whet owls nest in tree cavities or abandoned woodpecker holes. These holes are usually 2 to 12 m above the ground.

The female lays 4 to 7 eggs (usually 5 or 6). She incubates the eggs for 26 to 28 days. The chicks are altricial at hatching. Their eyes stay closed for the first 7 to 10 days, and they must be brooded by the female for several weeks. The male brings food to the nest for the female and the chicks. The female feeds the food to the chicks by tearing it up into small pieces. After 18 days, the female leaves the nest, but the male keeps bringing food to the chicks.

Chicks leave the nest when they 4 to 5 weeks old. They are able to fly, but the male parent continues to feed them for at least a month. They become independent from their parents after 6 to 8 weeks. When they are one year old, northern saw-whet owls grow adult feathers. They may also begin breeding at one year old. (Bisbee, 1998; Cannings, 1993; Tufts, 1986)

  • How often does reproduction occur?
    Northern saw-whet owls breed once yearly.
  • Breeding season
    Northern saw-whet owls breed between March and July.
  • Range eggs per season
    4 to 7
  • Average eggs per season
    5
    AnAge
  • Range time to hatching
    26 to 28 days
  • Range fledging age
    4 to 5 weeks
  • Range time to independence
    6 to 8 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Range age at sexual or reproductive maturity (male)
    1 (low) years

Male and female northern saw-whet owls have very different jobs as parents. The female owl chooses the nest site, lays the eggs and incubates them for 26 to 28 days. When the chicks hatch, she broods them for at least 18 days and tears their food into smaller pieces before feeding it to them. The male brings all of the food to the female and the chicks, and protects the nest area.

When the chicks are 18 days old, the female may begin helping the male hunt for food for the chicks, or she may leave the area. Some females leave the male to find another mate and raise another brood of chicks. The male stays with the chicks and feeds them for at least a month. (Cannings, 1993)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

How long do they live?

Captive saw-whet owls have lived as long as 16 years. In the wild, the longest known lifespan of a northern saw-whet owl was 7 years. (Cannings, 1993)

  • Range lifespan
    Status: wild
    7 (high) years
  • Range lifespan
    Status: captivity
    16 (high) years
  • Average lifespan
    Status: wild
    124 months
    Bird Banding Laboratory

How do they behave?

Northern saw-whet owls are nocturnal. They are active at night. During the day, they roost silently, hidden among thick vegetation. Northern saw-whet owls are also migratory. Most of these owls fly south in autumn. Northern saw-whet owls are also solitary, except during the breeding season when they form pairs. (Cannings, 1993; The Raptor Center, 2000; Tufts, 1986)

  • Range territory size
    1 (low) km^2

Home Range

The home ranges of two males that were tracked with radio transmitters were 1.42 and 1.59 square kilometers. (Cannings, 1993)

How do they communicate with each other?

Northern saw-whet owls communicate and perceive their environment using touch, sound and vision. They hunt using sight and sound. In fact, they have such good hearing that they can catch prey using just their ears to find it. Northern saw-whets use their eyes and ears to communicate. For example, males whose territories are next to each other may call back and forth to make sure that each stays in his own territory. During courtship, males call to females to attract them. Pairs use touch to strengthen the pair bond by allopreening (taking care of each others feathers). (Cannings, 1993; Government of Alberta, 2000; The Raptor Center, 2000; Tufts, 1986)

What do they eat?

Northern saw-whet owls hunt at night. They hunt from a low perch, where they watch and listen for prey. Saw-whet owls have excellent night vision, and excellent hearing. When they see or hear prey, the owl flies quickly to the prey, catching it with the large talons on their feet. Saw-whet owls tear their food apart with their beaks, and eat it in pieces. If they catch a large animal, they may store the leftovers to eat later.

Northern saw-whet owls mostly eat small mammals. Deer mice are their most common food, but voles, red-backed voles, shrews (g. Sorex, Blarina and Cryptotis), shrew-moles, pocket-mice, harvest-mice, bog lemmings, heather voles, red tree voles, jumping mice and house mice are also commonly eaten. Saw-whet owls sometimes catch larger mammals such as pocket-gophers, chipmunks and squirrels. They also eat some small birds and some insects, including beetles and grasshoppers. (Cannings, 1993; The Raptor Center, 2000)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • insects

What eats them and how do they avoid being eaten?

Large owls, such as great horned owls, long-eared owls and barred owls are probably the most common predators of northern saw-whet owls.

When a northern saw-whet owl is approached by a predator or a human at night, they give a call that sounds like “ksew”. During the day, if a predator comes near, the saw-whet owls stand up very straight and hold their feathers flat against their body. If the predator comes closer, the owls bob their head and shifting from foot to foot. They may defecate or snap their bill at the predator, but they will eventually fly away. (Cannings, 1993)

What roles do they have in the ecosystem?

Northern saw-whet owls affect the populations of small mammals that they eat. They also provide habitat for at least nine species of external parasites. (Cannings, 1993)

Do they cause problems?

There are no known adverse affects of northern saw-whet owls on humans.

How do they interact with us?

Northern saw-whet owls help humans by killing rodents that many people consider to be pests.

  • Ways that people benefit from these animals:
  • controls pest population

Are they endangered?

There are 200,000 to 600,000 northern saw-whet owls in the world. This number is probably getting smaller as the habitat that these birds need is being changed by logging. Nestling northern saw-whet owls that die usually die because they don’t have enough food, or because they have parasites. Adults are often killed when they are hit by vehicles.

Northern saw-whet owls are protected by the U.S. Migratory Bird Act and CITES Appendix II. They are not protected under the U.S. Endangered Species Act. (BirdLife International, 2004; Cannings, 1993)

Some more information...

The Northern Saw-Whet Owl's common name comes from the "skiew" call it makes when it is alarmed. This call is said to sound like a saw being whetted.

Contributors

Kari Kirschbaum (editor), Animal Diversity Web.

Jia Yan (author), West Windsor-Plainsboro High School, Joan Rasmussen (editor), West Windsor-Plainsboro High School.

References

"The Owl Pages - Northern Saw-Whet Owls" (On-line). Accessed July 12, 2000 at http://www.owlpages.com/species/nsawwhet/index.html.

BirdLife International, 2004. "IUCN Red List of Threatened Species" (On-line). Accessed December 03, 2004 at http://www.redlist.org/search/details.php?species=48588.

Bisbee, M. 1998. Meet Them at the Wildlife Park: The Saw-Whet Owl. The Gray News (online edition), Vol. 30, No. 1.

Cannings, R. 1993. Northern saw-whet owl (Aegolius acadicus). Pp. 1-20 in A Poole, F Gill, eds. The Birds of North America, Vol. 42. Philadelphia, PA: The Academy of Natural Sciences and Washington DC: The American Ornithologists Union.

Government of Alberta, 2000. "Alberta's Watchable Wildlife" (On-line). Accessed July 10, 2000 at http://www3.gov.ab.ca/srd/fw/watch/owl_saw.html.

Grondahl, C., J. Schumacher. "Northern Prairie Wildlife Research Center Home Page" (On-line). Accessed July 10, 2000 at http://www.npwrc.usgs.gov/resource/birds/owls/aegoacad.htm.

Long, K. 1998. Owls - A Wildlife Handbook. Boulder, Colorado: Johnson Books.

The Raptor Center, 2000. "Raptor Facts - Saw-Whet Owl" (On-line). Accessed July 10, 2000 at http://www.ahc.umn.edu/ahc_content/colleges/vetmed/depts_and_centers/raptor_center/index2.cfm?nav=53535&CFID=687163&CFTOKEN=88288799.

Tufts, R. 1986. "Nova Scotia Museum of Natural History: Birds of Nova Scotia" (On-line). Accessed July 10, 2000 at http://museum.gov.ns.ca/mnh/nature/nsbirds/bns0219.htm.

 
University of Michigan Museum of ZoologyNational Science Foundation

BioKIDS home  |  Questions?  |  Animal Diversity Web  |  Cybertracker Tools

Yan, J. 2001. "Aegolius acadicus" (On-line), Animal Diversity Web. Accessed September 23, 2014 at http://www.biokids.umich.edu/accounts/Aegolius_acadicus/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
Copyright © 2002-2014, The Regents of the University of Michigan. All rights reserved.

University of Michigan