The Silent Hunters
We’ve had a pair of Great Horned Owls (Bubo virginianus) around from the first day we moved into the house. Since they are both nocturnal and crepuscular (fly at dawn and dusk), they’re difficult to photograph. Occasionally we see them perched on one of the old Agave stalks in the evening or sitting on the roof edge of the house at night when we arrive home after dark. We see plenty of evidence that they frequent this area judging from the whitewash that’s left in the mornings.
The Hunter at Dusk
Owls are formidable hunters with extremely sensitive hearing and good eyesight. Owls pounce upon their prey silently thanks to the modified structure of the first primary wing feather which is serrated rather than smooth on the forward or leading edge. On the rare occasions we’ve flushed an owl in the wash, we noticed that they depart in complete silence.
One day I found this pellet under a lone mesquite that hangs over the driveway indicating that the owl probably roosted there overnight.
Great Horned Owl Pellet
A pellet consists of the indigestible parts of the owl’s prey items. As in all birds, owls have no teeth so they swallow their prey whole, if it’s small enough, or use their sharp beak to tear it into manageable pieces. Unlike other birds, owls have no crop (a pouch where food is stored for later consumption) so their meal goes directly into their two-part stomach. The first part is loaded with enzymes and other digestive juices. Then the contents are passed on to the gizzard, a muscular part of the stomach that lets the digestible material pass through to the small intestine while holding back all of the indigestible parts such as bones, fur and feathers. Taking up to 10 hours, the gizzard compresses this mass into a pellet like the one you see above. Then the pellet is sent back up to the first part of the stomach and regurgitated. Until the pellet is ejected from the stomach, the owl cannot eat.
In order to see what our owls have been eating, I dissected the pellet. There were a lot of rodent bones.
The matrix holding the bones together was a mass of fur. No bird feathers were found in this pellet.
There were large legs bones, some of which measured up to 28mm.
And there were at least six jawbones. The longest measured 30mm which points to a member of the rat family. We have plenty of White-throated Woodrats (Neotoma albigula) here (also known as packrats), so I suspect they are the source of most, if not all, of these bones. Other possibilities are Kangaroo Rat, Grasshopper Mouse and Deer Mouse.
Jawbones and other small bones
The largest jawbones
Great Horned Owl’s prey can consist of birds, small vertebrates and even insects. It will be interesting to dissect a few more pellets over the seasons and see how their diet changes.
Published by Arlene Ripley on January 27th, 2009 Tagged Arizona, Birds, Cochise County, Mammals, Nature
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