Birds
Great Grey Owl
Strix nebulosa · also called great grey owl, great gray owl, Lapland owl, Phantom of the North
The great grey owl is the “Phantom of the North” — a huge, round-faced grey owl that materialises out of a snowy forest, stares at you with small yellow eyes set in a face the size of a dinner plate, and then vanishes. It is the largest owl in the world by outline, and one of the least substantial: mostly feathers, hunting almost entirely by sound.
Overview
Great grey owls live in the boreal and montane conifer forests of the far north in both hemispheres — Canada, Alaska, the northern and western US, Scandinavia, and across Russia. They hunt in meadows, bogs, and forest openings, usually from a low perch, and they feed overwhelmingly on voles and pocket gophers. They are active by day and night, especially in the long twilight of a northern winter.
Big frame, small bird
At up to 84 cm long with a 1.5-metre wingspan, no owl looks bigger. But the great grey owl weighs only about a kilogram — its size is thick insulating plumage around a modest body. The great horned and eagle-owls are far heavier and stronger.
Hearing in three dimensions
The great grey owl has the largest facial disc of any raptor — a feathered dish that funnels sound to asymmetrically placed ears. The height offset lets the owl fix a rustling rodent in 3D by ear alone, even one moving under a metre of snow.
Snow-plunging
Having located prey purely by hearing, the owl plunges feet-first through the snow, punching through crust firm enough to hold a person and seizing a vole up to 45 cm down.
Irruptions
When northern vole populations crash, great grey owls move hundreds of kilometres south in irruptions — the winter of 2004–05 brought thousands into Minnesota and Wisconsin.
Status
The great grey owl is Least Concern, widespread across the northern forests, though locally sensitive to the logging of large old trees (it needs old nests and snags) and to road mortality.
Great Grey Owl: common questions
Is the great grey owl really the biggest owl?
By length and wingspan, yes — at up to about 84 centimetres long with a 1.5-metre wingspan, no owl is larger in outline. But it is a case of appearance versus substance. The great grey owl's enormous size is mostly an exceptionally thick, fluffy plumage insulating a relatively small body; it weighs only around a kilogram, sometimes less. The Eurasian eagle-owl, Blakiston's fish owl, and the great horned owl are all much heavier (2 to 4+ kilograms), stronger, and take far larger prey. So the great grey owl is the "biggest" owl in the sense of the largest silhouette, but not the most powerful.
How does it catch animals it can't see?
With extraordinary hearing and a purpose-built face. The great grey owl has the largest facial disc of any bird of prey — a wide, concave arrangement of stiff feathers that works like a satellite dish, collecting faint sounds and channelling them toward the ears, which are hidden at the edges of the disc and set at slightly different heights on each side of the skull. The height difference means a sound arrives at the two ears at fractionally different times and volumes depending on whether it is above or below the owl, so the bird can build a three-dimensional fix on a rustling vole. It will sit on a low perch, rotate its head to aim the disc, then drop, and it can locate and strike prey moving beneath a metre of snow. It hunts as much by night as in the low light of a northern winter day.
What is "snow-plunging"?
It is the great grey owl's signature winter hunting method. Having pinpointed a vole or gopher moving in its tunnels beneath the snow purely by ear, the owl launches from its perch, hovers briefly to fix the target, and then plunges feet-first straight down through the snow, punching through crust that can be firm enough to walk on and reaching prey up to about 45 centimetres deep. It then hauls itself and the catch back out. Getting this right requires the owl to correct for the way sound bends as it passes through snow, and young owls take time to master it.
Why do great grey owls sometimes appear far south of their range?
Because their food supply is boom-and-bust. Great grey owls depend heavily on voles, and northern vole populations rise and crash on multi-year cycles. In a winter when the voles collapse across a large region, the owls cannot find enough to eat and many move hundreds of kilometres south in search of prey — an "irruption." Famous irruptions, such as the one into Minnesota and Wisconsin in the winter of 2004–05 when thousands appeared, draw birdwatchers from across the continent, because a great grey owl hunting from a roadside fence post in daylight is otherwise a hard bird to find.