The Northern Saw-whet Owl (Aegolius acadicus) is a small, secretive owl found only in North America. Named for its call that resembles the sound of a saw being sharpened, this owl is an intriguing subject for bird watchers and researchers alike. This article delves into various aspects of the Northern Saw-whet Owl, including its habitat, diet, nesting habits, behavior, and conservation status.
Habitat and Distribution
Northern Saw-whet Owls inhabit woodlands of all types throughout their range, thriving over a range of altitudes and latitudes. They breed in forests across southern Canada and the northern and western United States, extending through central Mexico. These owls seem to prefer mature forests with an open understory for foraging, deciduous trees for nesting, dense conifers for roosting, and riverside habitat nearby. However, they exhibit adaptability by nesting in a wide range of wooded habitats, including coniferous swamps, disturbed deciduous woods, savannahs, riverside forests, and shrub-steppe habitats. They will also nest in boxes placed in coastal scrub, sand dune meadows, and poplar plantations. During the winter months, Saw-whets can be found in dense forests throughout their breeding range and across most of the United States, excluding the southernmost edges. Some remain all year on breeding range, others move south in autumn. Some western mountain birds may move downhill for winter. Migration is relatively early in spring, late in fall. Migrates at night.
Physical Characteristics
The Northern Saw-whet Owl is a tiny owl with a catlike face, oversized head, and bright yellow eyes, practically bursting with attitude. It is a small, short-bodied owl with a short tail. A very small owl with no "ear" tufts. Overall warm brown, with reddish streaks on white chest. The large rounded head has no ear tufts. The face is light brown, outlined in dark brown and white streaks. They have brown-and-white striped chests and bellies. Their large eyes are yellow. dark bills and streaked foreheads. Unlike the Western Screech-owl, Northern Saw-whet Owls don't have any ear tufts. Their facial disk is a light, buffy color and their backs are a darker brown speckled with white dots, almost as if someone splattered paint on them. Juvenile Northern Saw-whet Owls look quite different than the adults. Juvenile saw-whet owls have dark feathering on their wings and head and orange-colored chests, with the prominent white “v” between their eyes. The white “v” can be seen on adult saw-whet owls but it is accompanied by a predominantly white facial disk. They also have feathering down to their toes that helps keep them warm in cooler climates. Saw-whet owls are the fifth smallest owl in North America. The four species that are smaller are the northern pygmy owl (Glauciduim gnoma), ferruginous pygmy owl (Glaucidium brasilianum), flammulated owl (Otus flammeolus), and elf owl (Micrathene whitneyi). Adult plumage when they are one year old.
Diet and Hunting Behavior
Northern Saw-whet Owls eat mostly small mammals, hunting them at night from a low perch along the forest edge. The most common prey are deer mice and white-footed mice, but may include shrews, house mice, harvest mice, pocket mice, jumping mice, montane voles, red-backed voles, meadow voles, heather voles, red tree voles, shrew-moles, bats, and juveniles of larger mammals like pocket gophers, chipmunks, and squirrels. During migration they supplement their diet with birds, such as titmice, chickadees, kinglets, juncos, waxwings, sparrows, thrushes, wrens, warblers, robins, and even other small owl species. They may eat beetles, grasshoppers, moths, and bugs. Saw-whets that live along the coasts may eat intertidal invertebrates such as amphipods and isopods. Resident race on the Haida Gwaii islands, British Columbia, may eat crustaceans and insects in intertidal zone. Northern Saw-whet Owls eat deer mice. Males provide nearly all of the food while females are incubating and brooding the young. When hunting, Saw-whet Owls will often jump or pounce upon their prey. They have been known to catch many mice at once when there is a lot of food available.
Owls have no crop for food storage. They often swallow their food whole or in large chunks, and it goes directly to their stomach. In the stomach, a pellet (or cast) is formed from the fur, bones, and other indigestible material. The pellet is then regurgitated 10 or more hours later.
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Nesting and Reproduction
Northern Saw-whet Owl males choose and defend territories and call to attract females. The females choose the nest cavity, often an old nest hole made by a Northern Flicker or Pileated Woodpecker. Females probably choose the nest site, although males sometimes participate by perching in potential sites while giving their too-too-too call. The female lays 4 to 7 (usually 5 or 6) eggs at two-day intervals. They nest in previously excavated holes (usually those of Northern Flickers or Pileated Woodpeckers) in dead snags. They also use nest boxes. Nest site is in cavity in tree, usually 15-60' above ground. Mostly use abandoned woodpeckers holes, especially those of flickers and Pileated Woodpeckers. Nest Description Saw-whets lay their eggs on debris at the bottom of the cavity-such as woodchips, twigs, moss, grass, hair, small mammal bones, or old starling nests-without adding new material to the nest. Nest holes may be 8-44 feet off the ground, and they measure about 3 inches wide and 9-18 inches deep, with an entrance hole 2-3 inches across.
Nesting Facts:
- Clutch Size: 4-7 eggs
- Number of Broods: 1-2 broods
- Egg Length: 1.1-1.3 in (2.8-3.3 cm)
- Egg Width: 0.9-1.0 in (2.4-2.6 cm)
- Incubation Period: 26-29 days
- Nestling Period: 27-34 days
- Egg Description: White and smooth.
- Condition at Hatching: Semi-helpless and covered with white down, with eyes closed.
The female Northern Saw-whet Owl does the incubation and brooding. The male brings all the food needed while the female is incubating the eggs. She leaves the eggs for only one or two short trips each night, to defecate and cough up a pellet. The incubation period is 21 to 28 days. The female broods the chicks for at least 18 days. The female lays 4-7 eggs which she must incubate for the next 27-29 days. During this time, the male is busy finding food for himself and the female. After the chicks hatch, they keep their eyes closed for the first week to ten days. During this time, the female broods her young - covering them with her body to make sure they are protected from the elements and kept warm. The male must also continue to work hard, as he now has many extra mouths to feed. He will bring the food to the nest and the female will rip it into tiny pieces, delicately feeding each chick. As the chicks get a bit older, they are able to grasp and tear their own food. Young fledge at 4 to 5 weeks, and may leave the nest individually every 1 to 2 days, until they have all left. After about 4-5 weeks in the nest, the young will fledge, or fly for the first time. But, they are still dependent on their parents for up to two more months. At first, adult male brings all food to nest, female feeds it to young. Female remains with chicks until youngest is about 18 days old; then she may begin to hunt for them also, or may depart. Young leave nest at about 4-5 weeks, remain together near nest and are fed (mostly by male) for at least another 4 weeks. Female may sometimes find another mate and nest a second time in one year.
Behavior and Communication
Although saw-whets are usually monogamous, when prey is abundant each male may have more than one mate. Scientists believe that Saw-whet Owls are not monogamous, meaning they do not keep the same mate for life. Instead, each year the male must find a new female to raise young with. It isn't an easy job attracting a female, especially if there is a lot of competition. This is when Saw-whet Owls break out all the stops, polish off their vocal cords, and begin to sing. Male starts giving their too-too-too call as early as late January, before females arrive, and continue until May. Vocalize only during the breeding season which lasts from March to May. It is mostly silent throughout the rest of the year. When it does call, it, like most owls, has a full repertoire of hoots and whoops at its disposal. The Saw-whet’s call is similar to that of the Boreal Owl, but it is composed of separate notes, rather than notes that run together. They produce one or two notes per second and the series can last for minutes. When a female hears a male calling she responds with a high-pitched tssst call or a series of whistles. Once a female is enticed in by a male's call, she will respond with her own calls. The male might then present her with a gift. But instead of flowers or chocolates, he proudly gives her a dead mouse or other prey, which he carries to her in his beak. The male circles her about 20 times in flight before landing beside her and presenting a prey item. These owls have been observed allopreeing - which is when the males and females clean each others' feathers. This might be a way to help form a pair bond during the breeding season. Some year-round resident males or pairs probably maintain territories throughout the year, but each year they pair up with new mates.
Saw-whets are preyed on by larger raptors, including Eastern Screech-Owls, Spotted Owls, Great Horned Owls, Cooper’s Hawks, Broad-winged Hawks, and Peregrine Falcons. They roost during the day in thick conifers at an average of 11 feet above the ground, often hidden by foliage near the outer edge of a branch. They are occasionally discovered by mixed-species flocks of songbirds, which mob the predator in an effort to drive it away. Tuning in to all that commotion is one of the best ways for bird watchers to find these well-hidden owls. Northern Saw-whet Owls are strictly Nocturnal, with activity beginning at late dusk. Like many owl species, the Northern Saw-whet Owl is nocturnal, meaning it is most active at night. Around dusk, when most of us are just starting to wind down for the day, this owl's day is just starting. At this time, these owls wake up from their roost spot, stretch their wings and get ready for a night of hunting and feeding. The owls likely rest during the middle of the night and might become active again right at dawn, perhaps when many of us are still asleep. The Northern Saw-whet Owl has excellent low-light vision, and can easily find prey at night by sight. Its defense upon discovery is to sit still and not fly. move south in autumn. They detect prey by sight and sound. developed that they can locate prey by hearing alone. cues and vocalizations to communicate. may exchange calls to establish territorial boundaries. out of the perch onto the prey, capturing it with the talons. Northern Saw-whet owls impact the populations of small mammals that they eat.
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Adaptations for Nocturnal Hunting
Now, in order to help them maneuver in the dark, owls are equipped with some very special characteristics. First, their large eyes help them see in low light. Their eyes are so large, they have a bony ring around the eye, which protects the eye and gives it shape. This ring, known as the sclerotic ring, also keeps the eye in place so that owls are unable to move their eyes. To compensate for the lack of eye movement, owls have twice as many vertebrae in their necks as mammals, we have seven while they have 14. This allows them to turn their heads about 270 degrees each way (not the commonly believed 360 degrees) and gives them the ability to stand up very tall. Apart from their amazing eyesight, owls are also blessed with wonderful hearing thanks, in part, to their asymmetrical ear openings. If one were to examine the skull of the Northern Saw-whet Owl, they would notice that the right ear is higher on the head than the left, and each ear opening is a different shape. All owls have several characteristics that can be used to differentiate them from other raptors. For example, the leading edge of their flight feathers is serrated like a breadknife. This breaks up air turbulence and allows them to fly completely silently.
Conservation Status
Northern Saw-whet Owls are common and widespread, but their secretive lifestyle makes population trends difficult to identify with standardized surveys such as the North American Breeding Bird Survey or the Christmas Bird Count. The Northern Saw-whet Owl is considered to be of "Least Concern," which generally means that populations throughout its range are stable and that the species is relatively common. However, habitat loss due to logging and other actions may seriously threaten its nesting/breeding habitat. Partners in Flight estimates a global breeding population of 2 million and rate them 8 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Overall, their population has probably declined in past decades due to habitat loss. North Carolina and South Dakota have listed them as a species of special concern, and a subspecies native to the Queen Charlotte Islands of British Columbia is threatened. Although saw-whets breed in many forest types, they favor mature stands which may come under pressure for logging or development. People can maintain the suitability of forest habitat by allowing dead trees to remain standing to provide nest cavities. Saw-whets take readily to nest boxes, which can also be used to mitigate the loss of natural sites. Probably some declines in numbers with loss of habitat, but still widespread and fairly common. Though The Peregrine Fund doesn't work directly with Northern Saw-whet Owls, our efforts in scientific research, habitat conservation, education, and community development help conserve birds of prey around the world.
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