Region III Quarterly

Volume 3 - No. 2

April, 1941


By Natt N. Dodge,
Assistant Naturalist,
Southwestern National Monuments.

Bright moonlight flooded the desert, the dark shadows of the scrubby mesquite and scraggly creosote bushes contrasting sharply with the brightness of the lime impregnated soil. From my bed by the back wall of the 'dobe house, where I spent the summer nights, I looked around wandering, foggily, what had roused me. My eyes had almost fallen shut again, when I noticed a slight movement near the base of a clump of nearby saltbush. One of the many cottontail rabbits which occupy the square mile of Sonoran desert, which is Casa Grande National Monument, in Arizona, hopped casually across the open toward the shadow of a creosote bush. And then I was suddenly wide awake!

Great horned owl

From the branch of a mesquite tree 50 yards away a dusky figure launched itself upon broad wings and, silently as a shadow but true as an arrow's flight, glided earthward. There was a muffled thud, a shrill stifled cry, and a short struggle in the shadow of the creosote bush. Then with a soft beat of wide wings the Great Horned. Owl lifted itself into the air. For a moment I had a clear view of it in the bright moonlight, as half dragging, half carrying the rabbit, it rose heavily. Barely clearing a clump of saltbush, it gradually gained altitude and, once again a shadow in the moonlight, disappeared behind a corner of the old 'dobe house.

Great Horned Owls for many years have inhabited the famous Casa Grande. One of the first references to them was made by Dr. J. W. Fewkes, who carried on excavations in the ruins in 1906-1907. He stated, in referring to the supersititious fear with which the native Pima Indians held the old ruins, "The hooting of the owls which nest in the upper walls may add to the Pimas' dread of it."

The Pima Indians who occupy the nearby reservation are inclined to shun the ruins, particularly after sundown. That the owls may play a considerable part in this distrust is evidenced by the fact that monument personnel who have hired Pima girls as maids have encountered difficulty in getting them to stay on the monument over night. Once the girls have heard the voices of the owls emanating from the deep shadows beneath the broad shelter, they remember that they have important business at home on the reservation. The Pimas call the Great Horned Owl "Chu'koot", and believe that he is the soul spirit, or reincarnation of the Pima dead. Apparently many Pimas who retain the vestments of the living have no desire to meet the spirits of their relatives who have discarded their human bodies for a pair of wings.

Rangers conducting groups of visitors point out the owls, high among the rafters of the shelter, and find that people are univerrsally interested in them. Occasionally an old timer in the party will mention having seen the owls on some long-previous visit, and ask if these are the same birds. This might be a hard question to answer were it not for the fact that at least three of the birds are known to have met death. In 1909, M. French Gilman reported: "For at least four years, a pair of these owls has nested in the prehistoric Casa Grande ruins. Mr. Pinkley the custodian told me that the birds raised a brood each year in the old building and had never been molested except once, when one of them developed a decided taste for prize Wyandotte chickens. This was his undoing, but his widow secured another mate very soon and went on keeping house as if nothing had happened."

No semblance of a nest is built. The eggs are laid in a depression on the wall top. Observations conducted over a number of years indicate that brooding begins late in January or early in February. Usually four eggs are laid, evidently several days apart, as they apparently hatch at relatively lengthy intervals; at least, the nestlings vary considerably in size. The incubation period of this species is 28 days.

Prior to the commencement of the brooding, considerable evidence of excitemenet is noticed. Among records made in January are the the following: "Hooting begins at about 5:30 p. m. and continues until late at night. Both owl voices are heard and clucking sounds are interspersed between hoots." "At 8:30 p.m. I heard peculiar sounds issuing from the shelter. Mingled with soft, muffled hooting was a harsh call resembling a terrier-type dog trying to bark with something in its mouth."

Just when the eggs hatch is not definitely known, as the location of the nest is inaccessible without ropes and ladders, and the presence of this equipment disrupts the visitor use of the ruin. However, on numerous occasions early in March both adults have been seen together among the shelter rafters or, shortly after sunset, in the branches of mesquite trees west of the ruin. After the young birds have arrived, the adults show irritability, often snapping their beaks at visitors. A number of years ago, a visitor with small dog on leash was walking past the outside of the ruin when, without warning, one of the adults swooped silently from among the rafters, raked the dog's back with its talons, arid returned to its perch.

These owls can see sufficiently well in broad daylight to spot and catch small rodents. On one occasion, shortly after 9 o'clock in the morning, an adult was seen to swoop down from its shelter and pounce upon a ground squirrel, approximately 100 yards away. Carrying the prey in its talons, the bird flew back to the shelter, and was joined by four owlets. The youngsters flapped their wings and uttered harsh cries. Suddenly one of the young birds snatched the body of the squirrel from the talons of the parent owl, and flew down to the top of a lower wall with it.

On especially hot days, when the temperatures range around 115°, the owls frequently come down from their usual perches on the beams beneath the high center of the shelter and stand on the ruin walls. On a few occasions one has been seen on the floor of the center room of the ruin, apparently trying to escape the heat. During hot weather they are often seen to open their beaks and pant, as a domestic hen does on a hot day. Soon after sundown in summer all of the owls leave the shelter, one by one, and glide to nearby mesquite trees where they perch silhouetted against the sky. On hot evenings they are often seen with wings slightly raised and extended, as if in an effort to cool off. As dusk deepens, one will leave its perch flapping its wings to gain momentum, then sail across the desert in a long, low glide only a few inches above the tops of the creosote and salt bushes, to soar sharply upward on approaching another mesquite tree and settle lightly on one of its extended limbs.

Summer dusk is an exciting hour at the Casa Grande, for at this time the thousands of bats that inhabit the cracks of the mud walls arouse to squeaking and rustling activity. In black waves they fly from the building, and in twisting streamers pour out into the evening to disappear as dancing dots against the pink and lemon western glow. Ordinarily the owls pay them no heed but on one occasion I saw an owl, leaving the shelter, rare back in full flight and strike at a passing bat, first with one foot, then with the other. Whether the bird was simply annoyed or considered the bat as a possible meal is a question.

Although no serious studies of the food habits of the Casa Grande owls have been made, casual observations have been recorded. A number of undigestible pellets regurgitated by the owls were sent to specialists for identification, with the following results: Remains of 16 rabbits, 9 mice, 3 insects, and one bird were found in the analysis. Except for feathers of a mourning dove, only rabbit remains have been in and about the nest when it has been examined. Seasonal conditions undoubtedly cause diet variations. No ground squirrel remains were found in the pellets analyzed, whereas owls have twice been seen to capture these rodents. However, ground squirrels are in hibernation during the winter months, hence would not be available for the owls during the period that the pellets were collected. Feathers of the following birds have been found in the ruin, but whether they came from victims brought in by the owls is unknown: flicker, road runner, and mourning dove. One of the owls was observed with the body of a male sparrow hawk in its talons. Aside from the report made by Gilman in 1909, telling of the killing of chickens, there is no record of the Casa Grande owls preying upon domestic stock.

By midsummer the young owls are as large as their parents, and are able to manage themselves as skillfully in the air. However, their lighter-colored juvenile plumage and the absence of "ear" tufts or "horns", gives them an unmistakable round-headed appearance that serves to identify them. At night they give a harsh, rasping, screech entirely different from any part of the repertory of the adults.

Each summer, usually about the middle of July or the first of August, the adults disappear. The young, however, remain very much in evidence. Where or why the adults go is not known, but they are referred to as being "away on their summer vacation." The fact that an adult owl is occasionally seen with the young, indicates that they go no great distance, although, of course, the individual might be some stranger who dropped in for a visit. Usually the adults do not return until September, taking up their customary places on the beams of the shelter. Almost immediately following their arrival, the young ones disappear. To an observer with an active imagination, it appears that the adults stay with the young until they feel that the children are capable of taking care of themselves. After an absence of a month or six weeks, the old folks come home, take over the old roof, and chase the young ones out to fend for themselves. Whether this fanciful hypothesis comes anywhere near interpreting the story of what actually takes place in the Casa Grande owl family each year may some day be proved, possibly through a more complete banding program than has been possible in the past.

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Date: 17-Nov-2005