Saturday, April 10, 2010

Owl on the Prowl

We kicked off the spring field trip season this past week with visits from three Orchard Elementary School classes. On Thursday, Ms. Cox's fourth grade joined us for birding adventures on Norm's Island. Half-way through our hike we had already seen about ten species of local birds. But the best was yet to come. We rounded a corner, and in a cottonwood tree, only 50 feet from the trail, we spotted a Great Horned Owl (Bubo virginianus). This large owl can be up to two feet tall, with a wingspan of five feet. The female owls are larger than the males, though the males have deeper voices. An owl pair will call back and forth with the familiar "hoo hohoho hoo hoo". Check out the Cornell Lab of Ornithology website to listen to its call.
The owl sat motionless on the branch with the exception of its head, which swirled around backwards to look in our direction. We could see the tall tufts of feathers on its head; these are the "horns" for which it is named. All owls have excellent hearing and eyesight, which helps them to hunt at night. Their eyes are set facing forward in a dish-shaped face. The forward-looking eyes give the bird greater depth perception to help them hone in on prey. The dish shape helps to gather sounds, similar to how a satellite dish collects signals from the sky. This enables the owl to be a very effective predator!
Great Horned Owl nesting season occurs early, in January or February. This is when the males and females hoot to each other, oftentimes we hear them in the evening. When close they bow to each other, with drooped wings in a courtship display. Mutual bill rubbing and preening (cleaning of feathers) also occurs. They do not build a nest of their own but utilize the nests of other birds such as the hawk, crow and heron. They may also use squirrel nests, hollows in trees, abandoned buildings, or artificial platforms. They are extremely aggressive when defending the nest. Normally, two to four eggs are laid and incubated by the female for 26-35 days. Young owlets start roaming from the nest onto nearby branches at 6 to 7 weeks, but cannot fly well until 9 to 10 weeks old. They are fed for another few weeks as they are slowly weaned. Families remain loosely associated during summer before young disperse in the autumn. Adults tend to remain near their breeding areas year-round while juveniles disperse widely, over 250 km (150 miles) in the autumn. Territories are maintained by the same pair for as many as 8 consecutive years, however, these owls are solitary in nature, only staying with their mate during the nesting season. To learn more about this fascinating creature, check out the MT Fish, Wildlife, and Parks field guide pages.
Thanks to Ms. Cox's class for quietly observing this majestic bird with me!

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