Sawyer – Northern Saw-whet Owl

Sawyer is a Northern Saw-whet Owl (Aegolius acadicus) found in the bushes of someone’s backyard in 2013 so they brought her into the vet hospital. She sustained an injury that does not allow her to extend her left wing so she joined the club in August 2014. Her specific injury is unknown, but is most likely soft tissue damage because X-Rays did not show anything unusual. DNA testing would have to be done to know the sex of Sawyer since males and females do not differ in coloration; however females are on average 20% larger than males. Because of her larger size, Sawyer is suspected to be female. Sawyer came to us as an adult and because of that, we are unsure of her age.

Saw-whet Owls live in dense coniferous forests throughout Northern North America, and during the winter season Saw-whets can be seen in dense forests across central and south US as well. Many will migrate while others will stay in the same area year round. Migration occurs at night only and they have been known to cross very large bodies of water, over 70 miles. During the day-time, Saw-whets roost in very dense vegetation around 11 feet above ground often hidden by the foliage near the outer edge of the branches of evergreen trees. 

Sawyer

Nests are previously excavated holes usually made by woodpeckers that can be anywhere from 8-44ft off the ground. Mating season starts as early as late January and continues till May. Saw-whets are typically monogamous for the season, finding new mates every year, but if there is a good prey season females will take on more than one male. When nestlings are around 18 days old, females will leave the nest and males will continue to feed the young. 

Saw-whets usually hunt small rodents from a low perch along the forest edge, but can also hunt juveniles of larger mammals such as squirrels or chipmunks. They will also eat insects and during migration Saw-whets will supplement their diet with smaller bird species. Saw-whet Owls hunt primarily by sound.

Unlike other raptors, 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+ hours later. Because owls do not have a high enough stomach acidity to digest bones, larger owl pellets can easily be dissected to find the skeletons of their most recent prey. 

Another characteristic of owls is the large size of their eyes. They are so large, in fact, that there is no space for extrinsic muscles to move them. As a result, there is a bony ring around each eye that fixes them in place. While humans and most mammals can look to the left and right with their eyes without turning their head, owls cannot. To compensate for the lack of eye movement, owls have twice as many vertebrae in their necks as mammals, we have 7 while they have 14. This allows them to turn their heads about 270 degrees each way (not the commonly believed 360 degrees) as well as gives them the ability to stand up very tall. Owls, like many other birds, also have a clear third eyelid called the nictitating membrane that is used to protect their eyes while they are hunting.

Like all owls, Saw-whet Owls have a facial disc consisting of stiff feathers around their beak and eyes that directs sound back to their asymmetrically placed ears (one is more up and forward and the other down and backward, although which is which differs with species). This adaptation allows owls to locate their prey by triangulating the source of a sound. Some owls rely more on sound than others for hunting which can generally be told by the size ratio of their eyes to their facial disc. Saw-whets have relatively large facial discs compared to their eyes which tells you that they hunt primarily by sound. Owls with larger eyes and smaller facial discs like Great Horned Owls rely more heavily on sight for hunting, although hearing is still important.

Sawyer’s profile.

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. This makes it so the owls’ prey doesn’t hear them coming and so the sound of their wingbeats doesn’t interfere with the owls’ hearing.

Owls also have unique feet relative to most other birds. Instead of standing in the anisodactyl arrangement with three toes pointing forward and one pointing backward, they stand in the zygodactyl arrangement, with two toes forward and two backward. However, while hunting, owls have the ability to rotate their third toe forward into an anisodactyl arrangement.

Closeup of Sawyer’s feet and claws.

Saw-whet Owls are the 5th smallest owls in North America. The 4 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). Because they are so small in size and highly nocturnal, the Saw-whet Owl is very hard to spot. 

The name of the Northern Saw-whet Owl is derived from the sound of their voice which resembles “whetting” which is the sharpening of a saw. Usually this shrill call will be given many times in succession. Additional vocalizations include whines, gutteral sounds, tsst call, squeaks and high-pitched barks. 

Saw-whet Owls can be identified by their brown plumage, light colored facial disks, and lack of ear tufts which make them very round in appearance. They also have feathering down to their toes which helps keep them warm in cooler climates. Juvenile Saw-whet Owls have dark feathering on their wings and head and orange-colored chests, with the prominent white “v” between their eyes. They retain this juvenile coloring until they are 1 year old.

The white “v” can be seen on adult Saw-whet Owls but is accompanied by a predominantly white facial disk. These little owls are prey for larger owls and hawks and it is thought that the faint white “v” on the back of their head may help to fool their enemies. Predators avoid having their prey face them, and by having a “v” in front and behind them, a Saw-whet Owl may look like it has eyes on the back and front of its head! The idea is similar to butterflies that have patterns on their wings that look like eyes.

Categories: Raptors