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Archive for Sunday, October 25, 1998

THE GREAT HORNED OWL IS A FLYING PREDATOR WITH FEW EQUALS. SPECIAL TO THE JOURNAL-WORLD

October 25, 1998

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Thirty-five to 40 years ago, great horned owls nested in the city of Lawrence. The city was not exactly the metropolis it is today, but it wasn't a piece of prairie, either. I don't know all the places used by these big owls in those days, but the birds occurred regularly at least in what we now call Burcham Park and on the Kansas University campus. The owls mainly used the Natural History Museum.

A pair or succession of pairs nested on the north side of the museum, on a window ledge covered with English ivy, probably for several decades. The owls were very well-hidden from casual observers, and few people knew they were there. Students in ornithology sometimes took notes on the behavior of the owls and used the results for term papers and modest publications.

All this changed drastically in the early 1960s, when a major addition to the museum was constructed. The "New Wing," as the ornithologists tended to call the addition, completely covered the old north wall. The owls moved.

I don't know where they nested the first year of building construction, but in 1962 and 1963 they used a nook at the southeast corner of museum's seventh floor. This was right outside one of my office windows. The following year the pair nested on the east face of old Haworth Hall, near the corner of Jayhawk Boulevard and Mississippi Street. And thereafter they disappeared.

This suggests that great horned owls can live in close proximity to fair densities of humans if the ecologic setting is permissive. The birds were active by night, and fed on small mammals, which they caught in the park land south of Memorial Stadium, and pigeons, which they caught on the stadium and the museum, and perhaps on other buildings of the university.

Eventually the growing student population, as well as that of Lawrence in general, became a problem for the owls -- their foraging was disrupted, and their yearly production of young owls tended to leave the nest early, to their great disadvantage.

No place like home

Today Lawrence is much too busy and populated for big owls to use as they once did. Horned owls are now rare in the city, although some in Riverside Park sometimes cross over the Kansas River, visiting the Pinckney and Old West Lawrence neighborhoods. However, Douglas County and Kansas generally are favored by great horned owls. They use sheltered places for nesting -- caves, north-facing ledges on cliffs -- but frequently use old hawk or crow nests, which may be fairly well-exposed. In Florida, they like bald eagle nests, which they can appropriate from eagles active at the nest.

Great horned owls are rightly considered to be among the most aggressive and effective predators among all birds. Part of this is a result of their mind-set -- they are aggressive, although unfocused, the day they hatch. The other part of their effectiveness is how they are built. Relative to other birds, or even other avian predators, a disproportionately large fraction of their bone and muscle mass is in their legs. These great appendages end in four massive talons, which are among the world's most effective mammal traps. A relatively small fraction of bone and muscle is allotted to flight, even though the wings are reasonably long and broad.

Night vision prowess

Nocturnal vision of owls is famous for its effectiveness at low light intensity. Under conditions that we consider to be total darkness, owls can see well enough to catch mice and other prey. Additionally, a part of owls' capabilities at nighttime hunting is owing to acute hearing. Their external ears (unrelated to the feather tufts we call "horns") are asymmetrically placed on their heads so that locating the source of sound made by a prey animal is relatively easier than for most predators.

If the horns of great horned owls are not ear tufts, or, for that matter, horns, what are they? Their function has not been unequivocally determined, but almost certainly lies in signal communication with other great horned owls. The feathers are erected under stress, and such an owl may be expected to be aggressive. But the full range of use of the tufts is yet to be understood by ornithologists.

Small pet advisory

Great horned owls are found from the arctic of Alaska and Canada to Tierra del Fuego, excluding the humid tropics and much of the insular Caribbean region. A sister species, the eagle owl, occurs widely in Eurasia, and congeners are found in more tropical parts of the Old World. All these owls are characterized by large size and an aggressive physical presence, and are among the most capable of all avian predators.

Our horned owls nest and roost in woodland sites, and hunt there, as well as in prairie and farmland. They eat mostly voles, mice and rabbits, but often take other mammals as well as a variety of birds. A recent Internet posting on the Kansas Bird List notes that a great horned owl near Winfield has been eating meadowlarks, nighthawks and a blue-winged teal. Horned owls also catch other species of owls, other predatory birds, and are fully capable of taking house cats, small dogs and other small mammalian predators, such as young foxes and skunks. Their effectiveness is a consequence of their massive feet and sharp talons, which are used to suffocate prey as well as puncture circulatory and nervous systems.

I have implied a remote prospect of losing a pet to a horned owl, and I do this only because it occasionally happens. The implication also lends a certain drama to an otherwise sober account of a familiar bird. But the probability of losing a pet is vanishingly small, and of no concern to almost all of us. For many decades I have lived in places in New Mexico and Kansas that were (and are) heavily populated with great horned owls, and know of no instance in which dogs and cats have been molested by such an owl. Even so, I enforce an 8 p.m. curfew on pet cats.

-- Richard Johnston is an emeritus professor at the Museum of Natural History and Biodiversity Research Center at Kansas University, and a member of the Kansas Ornithological Society.

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