The Northern Saw-whet Owl (Aegolius acadicus) is a small owl native to North America. The scientific description of one of the sub-species of this owl is attributed to the Rev. John Henry Keen who was a missionary in Canada in 1896. Adults are 17–22 cm (6.7–8.7 in) long with a 42–56.3 cm (16.5–22.2 in) wingspan. They can weigh from 54 to 151 g (1.9 to 5.3 oz) with an average of around 80 g (2.8 oz), making them one of the smallest owls in North America. They are close to the size of an American Robin.
The Northern Saw-whet Owl has a round, light, white face with brown and cream streaks; they also have a dark beak and yellow eyes. They resemble the Short-eared Owl, because they also lack ear tufts, but are much smaller. The underparts are pale with dark shaded areas; the upper parts are brown or reddish with white spots. They are quite common, but hard to spot.
The Northern Saw-Whet Owl makes a repeated tooting whistle sound. Some say they sound like a saw being sharpened on a whetstone. They usually make these sounds to find a mate, so they can be heard more often April through June when they are looking for mates. Despite being more common in spring, they do vocalize year round.
Their habitat is coniferous forests, sometimes mixed or deciduous woods, across North America. Most birds nest in coniferous type forests of the North but winter in mixed or deciduous woods. They also love riparian areas because of the abundance of prey there. They live in tree cavities and old nests made by other small raptors. Some are permanent residents, while others may migrate south in winter or move down from higher elevations. Their range covers most of North America including southeastern Alaska, southern Canada, most of the United States and the central mountains in Mexico. The map shows where they breed and the areas where they can live throughout the year.
Some have begun to move more southeast in Indiana and neighboring states. Buidin et al. did a study of how far north the Northern Saw-whet owls breed and they found that they can breed northward to > 50º N, farther than ever recorded before. Their range is quite extensive and they can even breed in the far north where most birds migrate from to breed. They are an adaptive species that can do well in the cold.