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 had 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 it 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.
Facts about the northern saw-whet owl
Hunting & diet:
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 or more 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.
Mating & nests:
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. Mating season starts as early as late January and continues until May. When nestlings are around 18 days old, females will leave the nest and males will continue to feed the young. Nests are previously excavated holes usually made by woodpeckers that can be anywhere from 8 to 44 feet off the ground.
Wings: 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.
Eyesight: 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 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. Owls, like many other birds, also have a clear third eyelid called the nictitating membrane that is used to protect their eyes while hunting.
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). 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” or the sharpening of a saw. Usually this shrill call will be given many times in succession. Additional vocalizations include whines, guttural 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 that 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 a year old.
The white “v” can be seen on adult saw-whet owls but it is accompanied by a predominantly white facial disk. These little owls are prey for larger owls and hawks and it is thought 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.