GREAT HORNED OWLS
By Natt N. Dodge,
Assistant Naturalist,
Southwestern National Monuments.
Bright moonlight flooded the desert, the dark shadowsof the scrubby mesquite and scraggly creosote bushes contrasting sharplywith the brightness of the lime impregnated soil. From my bed by theback wall of the 'dobe house, where I spent the summer nights, I lookedaround wandering, foggily, what had roused me. My eyes had almost fallenshut again, when I noticed a slight movement near the base of a clump ofnearby saltbush. One of the many cottontail rabbits which occupy thesquare mile of Sonoran desert, which is Casa Grande National Monument,in Arizona, hopped casually across the open toward the shadow of acreosote bush. And then I was suddenly wide awake!
GREAT HORNED OWL.
From the branch of a mesquite tree 50 yards away adusky figure launched itself upon broad wings and, silently as a shadowbut true as an arrow's flight, glided earthward. There was a muffledthud, a shrill stifled cry, and a short struggle in the shadow of thecreosote bush. Then with a soft beat of wide wings the Great Horned. Owllifted itself into the air. For a moment I had a clear view of it in thebright moonlight, as half dragging, half carrying the rabbit, it roseheavily. Barely clearing a clump of saltbush, it gradually gainedaltitude and, once again a shadow in the moonlight, disappeared behind acorner of the old 'dobe house.
Great Horned Owls for many years have inhabited thefamous 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. Hestated, in referring to the supersititious fear with which the nativePima Indians held the old ruins, "The hooting of the owls which nest inthe upper walls may add to the Pimas' dread of it."
The Pima Indians who occupy the nearby reservationare inclined to shun the ruins, particularly after sundown. That theowls may play a considerable part in this distrust is evidenced by thefact that monument personnel who have hired Pima girls as maids haveencountered difficulty in getting them to stay on the monument overnight. Once the girls have heard the voices of the owls emanating fromthe deep shadows beneath the broad shelter, they remember that they haveimportant business at home on the reservation. The Pimas call the GreatHorned Owl "Chu'koot", and believe that he is the soul spirit, orreincarnation of the Pima dead. Apparently many Pimas who retain thevestments of the living have no desire to meet the spirits of theirrelatives who have discarded their human bodies for a pair of wings.
Rangers conducting groups of visitors point out theowls, high among the rafters of the shelter, and find that people areuniverrsally interested in them. Occasionally an old timer in the partywill mention having seen the owls on some long-previous visit, and askif these are the same birds. This might be a hard question to answerwere it not for the fact that at least three of the birds are known tohave met death. In 1909, M. French Gilman reported: "For at least fouryears, a pair of these owls has nested in the prehistoric Casa Granderuins. Mr. Pinkley the custodian told me that the birds raised a broodeach 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 andwent on keeping house as if nothing had happened."
No semblance of a nest is built. The eggs are laid ina depression on the wall top. Observations conducted over a number ofyears indicate that brooding begins late in January or early inFebruary. Usually four eggs are laid, evidently several days apart, asthey apparently hatch at relatively lengthy intervals; at least, thenestlings vary considerably in size. The incubation period of thisspecies is 28 days.
Prior to the commencement of the brooding,considerable evidence of excitemenet is noticed. Among records made inJanuary are the the following: "Hooting begins at about 5:30 p. m. andcontinues until late at night. Both owl voices are heard and cluckingsounds are interspersed between hoots." "At 8:30 p.m. I heard peculiarsounds issuing from the shelter. Mingled with soft, muffled hooting wasa harsh call resembling a terrier-type dog trying to bark with somethingin its mouth."
Just when the eggs hatch is not definitely known, asthe location of the nest is inaccessible without ropes and ladders, andthe presence of this equipment disrupts the visitor use of the ruin.However, on numerous occasions early in March both adults have been seentogether among the shelter rafters or, shortly after sunset, in thebranches of mesquite trees west of the ruin. After the young birds havearrived, the adults show irritability, often snapping their beaks atvisitors. A number of years ago, a visitor with small dog on leash waswalking past the outside of the ruin when, without warning, one of theadults swooped silently from among the rafters, raked the dog's backwith its talons, arid returned to its perch.
These owls can see sufficiently well in broaddaylight to spot and catch small rodents. On one occasion, shortly after9 o'clock in the morning, an adult was seen to swoop down from itsshelter and pounce upon a ground squirrel, approximately 100 yards away.Carrying the prey in its talons, the bird flew back to the shelter, andwas joined by four owlets. The youngsters flapped their wings anduttered harsh cries. Suddenly one of the young birds snatched the bodyof the squirrel from the talons of the parent owl, and flew down to thetop of a lower wall with it.
On especially hot days, when the temperatures rangearound 115°, the owls frequently come down from their usual percheson the beams beneath the high center of the shelter and stand on theruin walls. On a few occasions one has been seen on the floor of thecenter room of the ruin, apparently trying to escape the heat. Duringhot weather they are often seen to open their beaks and pant, as adomestic hen does on a hot day. Soon after sundown in summer all of theowls leave the shelter, one by one, and glide to nearby mesquite treeswhere they perch silhouetted against the sky. On hot evenings they areoften seen with wings slightly raised and extended, as if in an effortto cool off. As dusk deepens, one will leave its perch flapping itswings to gain momentum, then sail across the desert in a long, low glideonly a few inches above the tops of the creosote and salt bushes, tosoar sharply upward on approaching another mesquite tree and settlelightly 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 themud walls arouse to squeaking and rustling activity. In black waves theyfly from the building, and in twisting streamers pour out into theevening to disappear as dancing dots against the pink and lemon westernglow. Ordinarily the owls pay them no heed but on one occasion I saw anowl, leaving the shelter, rare back in full flight and strike at apassing bat, first with one foot, then with the other. Whether the birdwas simply annoyed or considered the bat as a possible meal is aquestion.
Although no serious studies of the food habits of theCasa Grande owls have been made, casual observations have been recorded.A number of undigestible pellets regurgitated by the owls were sent tospecialists for identification, with the following results: Remains of16 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 inand about the nest when it has been examined. Seasonal conditionsundoubtedly cause diet variations. No ground squirrel remains were foundin the pellets analyzed, whereas owls have twice been seen to capturethese rodents. However, ground squirrels are in hibernation during thewinter months, hence would not be available for the owls during theperiod that the pellets were collected. Feathers of the following birdshave been found in the ruin, but whether they came from victims broughtin by the owls is unknown: flicker, road runner, and mourning dove. Oneof the owls was observed with the body of a male sparrow hawk in itstalons. Aside from the report made by Gilman in 1909, telling of thekilling of chickens, there is no record of the Casa Grande owls preyingupon domestic stock.
By midsummer the young owls are as large as theirparents, 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 appearancethat serves to identify them. At night they give a harsh, rasping,screech entirely different from any part of the repertory of theadults.
Each summer, usually about the middle of July or thefirst of August, the adults disappear. The young, however, remain verymuch in evidence. Where or why the adults go is not known, but they arereferred to as being "away on their summer vacation." The fact that anadult owl is occasionally seen with the young, indicates that they go nogreat distance, although, of course, the individual might be somestranger who dropped in for a visit. Usually the adults do not returnuntil September, taking up their customary places on the beams of theshelter. Almost immediately following their arrival, the young onesdisappear. To an observer with an active imagination, it appears thatthe adults stay with the young until they feel that the children arecapable of taking care of themselves. After an absence of a month or sixweeks, the old folks come home, take over the old roof, and chase theyoung ones out to fend for themselves. Whether this fanciful hypothesiscomes anywhere near interpreting the story of what actually takes placein the Casa Grande owl family each year may some day be proved, possiblythrough a more complete banding program than has been possible in thepast.