Article by Mike Furber
One could hardly imagine a more endearing predator: diminutive, fierce, stealthy, tenacious, and resilient, this smallest of eastern North American owls is rarely observed accept in the winter or during migration at owl banding stations. Indeed, Saw-whet Owls were thought to be much less common until owl banding throughout North America and station networks such as Project Owl-Net revealed many more owls passing through on fall migration than was ever previously thought.
This small robin-sized, chestnut and whitish owl with a proportionately large head and huge yellow eyes, is one of a few species of owls that migrate seasonally in a true sense. The related slightly larger, grayish-brown, more northern Boreal Owl does to some degree, as does the larger tufted rusty-faced Long-eared Owl with some regularity. Great Gray Owls, Snowy Owls and Northern Hawk Owls have moved south in large numbers every few years this being called various names like incursion, or invasion. Some owls, such as the Short-eared Owl have been found to be quite erratic and extremely unpredictable as migrants or even nesting residents for that matter.
We have learned some interesting things about Saw-whet Owls in the last few decades – much of it from banding. With more females being banded one might think that females were more likely to respond to audio lure recordings; however, the same proportion of females were being caught even without audio lures. Further investigation has shown that females are much more likely to move further south; alternately, males are more likely to winter farther north closer to the nesting grounds to have a head start in early spring.
March is the time males will select a nesting territory with vocal whistle-like repetitive single “toot” calls that can continue monotonously, sounding very like miniature alien invaders. In fact, the name “Saw-whet” was apparently derived from some variations of this nuptial calling, but it doesn’t seem a very accurate rendering. Nevertheless, the name has stuck as most strange names do. The species epithet, acadicus, from the full scientific name, Aegolius acadicus, was derived from the discovery and description of this owl in old Acadia (now Nova Scotia). Consequently, some think that the name “Acadian Owl” would be a nicer official name and we agree. Being migrants, with different gender migration patterns, it follows that saw-whets do not mate for life. What’s more, they don’t even have site fidelity – that is an attachment to the same areas including both wintering and breeding locations. Therefore, Saw-whets are more nomadic than previously thought.
April is the time of nesting. Although the mixed hardwood conifer forests of the southern Canadian Shield and the Appalachians are often favoured, they have been found to nest in predominantly deciduous forests further south as well as coniferous forests to the north. Spruce bogs and balsam fir stands near wetlands are excellent examples. The nest itself, however, is usually in a hardwood such as an aspen or poplar, previously fashioned and used by a Northern Flicker or a Pileated Woodpecker. A normal clutch is four to six eggs with incubation close to a full month by the female. The male provides food for the female and the young. Food is mostly deer mice (Peromyscus sp.) and voles (Microtus sp.) of various types; small birds are occasionally taken. Even after the young have left the nest the male is the main provider and protector – cheers for paternal performance!
An interesting phenomenon among owls and raptors is what is referred to as reversed sexual dimorphism: the idea that females tend to be larger than males – the opposite of most bird species where males are usually slightly larger. Many theories have been put forward and investigated, but all explain the advantage of sexual dimorphism to some degree, but not the reversed gender situation satisfactorily. Suffice it to say, the females are considerably larger than males by as much as 20 to 25%. This may help to open a broader food niche for the saw-whet offsetting some food competition between the sexes. The main foes of the saw-whet are Barred Owls and Screech Owls, the saw-whet being a frequent item on the food menu of these two-owl species – particularly during migration. The other frequent danger for saw-whets are collisions with human transportation vehicles – this being the most frequent injury of Saw-Whet Owls admitted to rehabilitation centres across North America.
So, if you want to see a Saw-whet Owl, check out plantations of White Pine or spruce and White Cedar groves in the winter – these are likely to be males here in Southern Ontario. Or better yet, check out a banding station in the fall (October) such as Ruthven Park where migration monitoring is carried out annually. You will be smitten by a breath-taken close-up of this darling owl species – be ready for maximum cuteness in this nocturnal gnome!