Tundra – Snowy Owl

Tundra is a male Snowy Owl (Bubo scandiacus) who came to the WSU Veterinary Teaching Hospital in December of 2011. He was most likely hit by a car, and had two injuries to his left wing – a fractured radius/ulna and a dislocated elbow. The radius/ulna healed well, but the dislocation is irreparable. Because Tundra can no longer fully extend his left wing, he will never be able to fly.

Snowy owls spend the summer in the very far northern reaches of the Arctic, where they breed. In the winter they migrate south, but usually only as far as southern Canada. However, these owls will occasionally have a very successful breeding year, and a sudden increase in population will cause them to spread much farther south into the United States. Tundra was found near Spokane during one of these population events, known as an “irruption”. In the winter of 2011-2012, snowy owls were seen as far south as Idaho, Missouri, Oklahoma, and Massachusetts.

Tundra

Snowy owls nest on open ground in a shallow depression called a “scrape”. They do not nest on the snow. They will fiercely defend their nest from predators, including wolves. 

Male and female snowy owls are somewhat sexually dimorphic. Young males have a white bib and a white spot on the back of the head, with dark brown barring on the rest of the body which fades as they get older. Old male snowy owls can become almost pure white. Female snowy owls keep the dark bars throughout their life. While there is some overlap, the whitest snowy owls will always be males, and the darkest owls will always be female. All snowy owls have bright yellow eyes.

Their main prey is the lemming. When necessary, they will also hunt other small rodents, rabbits, waterfowl, or even fish. The owl will sit for most of the day, watching and listening for food. When prey is spotted, they will swoop silently down to catch it in their powerful talons. Like the great gray owl, the snowy owl can detect rodents tunneling under the snow completely by sound. They are able to fly down and “punch” through the snow to catch their meal.

Tundra’s profile.

Another characteristic of owls is the large size of their eyes. They are so large, in fact, that there is no space for extrinsic muscles to move the eyes. As a result, there is a bony ring around each eye that fixes them in place. While humans and most mammals can look to the left and right with their eyes without turning the head, owls cannot. To compensate for the lack of eye movement, owls have twice as many vertebrae in their neck as mammals – we have 7, they have 14. This allows them to turn their head completely backwards and then over the opposite shoulder. While they cannot rotate their head 360 degrees in each direction as many people believe, they can rotate it about 270 degrees each way. Because of the large number of vertebrae, owls can also extend their neck up to look taller and thus more imposing to any predators.

Another unique owl characteristic is that the front edges of their primary flight feathers are serrated like a bread knife. This breaks up air turbulence and allows them to fly almost completely silently. There are two purposes for this – for one, owls do not want their prey to hear them coming. The second reason is that owls depend so much on their hearing that any noise from their wings would hinder their hunting ability.

Owls also have unique feet relative to most other raptors. Instead of standing with three toes in front and one toe pointing backwards (known as the anisodactyl arrangement), they stand with two toes forward, and two pointing backwards (known as a zygodactyl arrangement). However, while hunting, owls have the ability to rotate their third toe forward into an anisodactyl arrangement.

Closeup of Tundra’s feet and claws.

The snowy owl is considered the largest and heaviest owl in North America. The great horned owl and the great gray owl come close, but neither quite has the body mass or wingspan to compare to the snowy.

Categories: Raptors