Scientific Name: Aegolius acadicus
(Information for this species page was gathered in part by Ms. Kristin Baer for an assignment in Biology 220W, Spring 2007)
The northern saw-whet owl (Aegolius acadicus) is a year-round resident of Pennsylvania and an overwintering migrant species of states to our east, west, and south. Its unusual name is derived from the sound of its calls. These calls have been variously described as resembling the sound of water dripping into a half-filled pail or the pinging that is generated when a saw blade is being sharpened (or “whetted”). The northern saw-whet vocalizes only during its breeding season (March to May) and uses its song both to attract mates and to mark its breeding territory.
Mating and Reproduction
Females typically lay 5 or 6 white, oval eggs and then will, with only occasional short trips away from the nest for defecation or pellet regurgitation, continuously incubate the clutch for 21 to 28 days. During this incubation period the male will bring the female food but will not actually participate in the nest brooding. There have been observations of males caring for more than one female on nests at one time, but this must have occurred in habitats with very abundant food supplies.
The females remain in the nest and keep the tree hole very clean during the incubation period and through the first 2 ½ weeks of the nestlings’ lives. The owlets grow very rapidly, though, and 18 days after egg hatching, the female begins to roost outside of the tree hole. In the next 2 weeks before the owlets fledge the nest cavity will steadily fill with feces, rotting pieces of uneaten prey, and regurgitated pellets. Survival of the entire cohort of nestlings depends on the local abundance of prey. If prey densities are limiting, the younger, latter hatching owlets will not survive.
The fledged owlets roost together near the brood nest for the next 4 weeks. During this period of time they are fed, primarily by the male. During this period of time the female, liberated from the maintenance duties of her brood, may mate with another male and begin the rearing of a second clutch of eggs.
Like all owls, the saw-whet relies on intestinal enzymes to break down the digestible body parts of its food. The un-digestible hair, bones, claws, feathers, or arthropod exoskeletons are then regurgitated in the form of a pellet. Examination of these pellets is an excellent way to access the specifics of an owl’s diet.
The northern saw-whet owl is a widely distributed and relatively common species throughout large sections of North America. Its small size, excellent camouflage, and preference for relatively unmanaged habitats, though, make its sighting an uncommon experience. As long as complex woodland habitats are maintained, however, the saw-whet owl will continue to liven spring nights with its calls and help to keep wild deer mice populations under control.
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This page was last updated on
October 8, 2013