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Ask Cam

It's lonely at the top

March 5, 2009

Question:

Cam, Where did the owls go that had a nest in the pine by the President's Office? I saw them last fall but haven't seen them since.

Cam’s answer:

Wish I could ask my feathered friends - but I haven't seen them around lately, either! Over the years, great horned owls (Bubo virginianus – what a great name, yes?) have nested in the tall blue spruce on the southeast corner of the Administration Building, but the beautiful birds have been absent so far this year. I’m pretty sure they haven’t lost their nest eggs because of the mortgage crisis, since great horned owls don’t use the same contracts for housing that you humans do.

To find out some possible reasons for the empty nest, I talked with Jesse Barber, a Postdoctoral Fellow in Fish, Wildlife, and Conservation Biology.

“Great horned, like all owls, don't build their own nests, so it could be that the hawk or crow’s nest the owl was using was blown down or damaged, forcing the owl to move on,” Jesse told me. “Alternatively, thermal regimes of nests sometimes change – a new structure blocking the sun, for example, or even trimmed branches exposing a nest to intense sunlight in the warmer months may cause abandonment.

"On a more somber note, one of the biggest threats to owls are automobiles. The great horned could have been hit. It’s unlikely that the prey base is a factor, but competition from other owls could be...it’s hard to be certain.”

Ronald Ryder, emeritus professor of fishery and wildlife biology, said owls have been nesting on the Oval and near the Administration Building for quite a few years and that the birds have been extensively studied and banded. Staff members of the Rocky Mountain Raptor Program and the Veterinary Teaching Hospital have helped study and treat the birds.

In fact, the owls were the subject of lengthy research from 1992-98 by Kuni and Harumi Suzuki, who published "Ecology and Natural History of Great Horned Owls in an Urban Habitat" in the July 1998 Journal of the Colorado Field Ornithologists. The couple reported that the owl territory on the eastern half of campus was occupied almost continuously, though not by the same pair, from the time the study began.

And, while the Suzukis observed that successful pairs of owls typically produce two young per year, not all young – or adults – survive. Some eggs never hatch, or fledglings die or become orphans due to adult death from disease, starvation, man-made hazards, or unknown causes. It’s a tough life out there!

I should also mention that there’s still a camera on the third floor of the Administration Building looking out over the (now) empty nest. Check out the Owl Cam and keep me posted if you see anybody moving into the neighborhood.

Thanks for giving a hoot!