We have three small owls that share a lot of characteristics. They are the boreal owl (Aegolius funereus) of North America and Eurasia, known as Tengmalm’s owl in Eurasia, and in North America the northern saw-whet owl (A. acadicus) and the western screech owl (Megascops kennicottii). In our area, they are forest birds (although the screech owl also breeds in the dry southwest, and I will not discuss those populations here). None of the three is very common in our area. The quite different pygmy owl is small too, but that one occupied a whole essay by itself, so here I’ll say a bit about three others.<\/p>\n\t\t\t\t
They range in size from about seven or eight to ten inches in length, with wing spans of about 17 to 21 inches. Body weights vary seasonally, so an average isn’t very meaningful, but in general they weigh less than 200 grams. Females are larger than males. The main predators on juveniles and adults are large raptors; marten and squirrels may prey on eggs and chicks.<\/p>\n\t\t\t\t
These three species are similar in many ways. They are mostly nocturnal hunters (except in the far north when summer has no night or if chicks are unusually hungry), able to find prey in the dark and under cover. They can locate prey by sound: their ears are asymmetrical in shape and in location on the side of the wide skull, so sounds arrive differently on right and left sides, allowing them to pinpoint prey location. They have facial discs of specialized feathers that help collect sounds and direct them to the ears. They are generally sit-and-wait predators, waiting for signs of prey presence and then swooping down to grab prey in their talons. Their prey is mainly small mammals, with some birds, insects, and occasionally other things. Prey may be cached on tree branches near roost sites or in cavities, especially during the nesting season.<\/p>\n\t\t\t\t