In the desert regions of our southwestern borders, this gay little woodpecker is one of the commonest, noisiest, and most conspicuous birds, always much in evidence, and always seeming to protest, in whining tones, the intrusion of strangers. Its center of abundance seems to be on the great desert mesas of southern Arizona, where the infertile soil is scantily covered with a scattered growth of creosote bushes, low mesquites, an occasional cholla or barrel cactus and dotted with single specimens or little groups of the giant cactus, or saguaro. But it is also common in the river bottoms, covered with a heavier growth of mesquite, and in the canyons of the foothills among the cottonwoods, willows, and sycamores. It ranges from an elevation of 2,500 feet on the mesas up to 4,000, or even 4,500, feet in the canyons and foothills.
In this region, it is a dominant species and a very useful neighbor, even if unintentionally, for the many species of birds and small mammals for which it provides homes. M. French Gilman (1915) puts it very well as follows:
Were it not for the Gila woodpecker (Centurus uropygialis) what would become of the several species of birds that use already prepared cavities for their domiciles? In some cases these tenants do not even await the pleasure of the excavators, but take forcible possession. In holes excavated by Gila woodpeckers there may regularly be found nesting the elf owl, ferruginous pigmy owl, ash-throated flycatcher, and Arizona crested flycatcher. Occasionally a cactus wren makes use of the handy hollow, and once I saw one occupied by a Lucy warbler. A big “rough-neck” scaly lizard frequents the holes when not too high in the cactus, and in two holes in willow trees I found snakes. It is not pleasant to insert one’s hand and have a big lizard or snake crawl up the arm to escape. Rats and mice are sometimes found in the deserted holes, especially if the tree be much decayed and with cracks and hollows connecting holes at different heights in the tree or branch. So these woodpeckers may be considered among the class of innocent or unintentional benefactors.
In addition to the species mentioned by Mr. Gilman above, we found saguaro screech owls, desert sparrow hawks, and western martins nesting in the old holes made by woodpeckers. Some of these holes were doubtless made by Mearns’s gilded flickers, perhaps those that were used by the larger species, as this woodpecker is fairly common in the same region and nests regularly in the saguaros. These old holes make ideal nesting sites, for the sap of the cactus hardens around the excavations, making them fairly permanent nesting boxes; I have seen these gourd-shaped pockets still persisting in fallen saguaros, where the pulp had all rotted away, leaving only the skeleton ribs of the dead giant.
Nesting.—While collecting with the late Frank C. Willard in southern Arizona in 1922, we examined seven occupied nests of the Gila woodpecker. The first of these was found on May 17, at Fairbank, in the valley of the San Pedro River; the nest was a cavity 15 inches deep in a dead branch of a cottonwood, 15 feet above ground. Five days, May 19 to 23, were spent in Pima County, in the vicinity of Tucson, between the mesquite forest in the valley of the Santa Cruz River and the southern end of the Santa Catalina Mountains. Two nests were found in the mesquite forest on May 19, both in mesquite trees, one 20 and one 25 feet from the ground; one contained only a single fresh egg and the other held a brood of young. We had an interesting experience here the next day. While crossing the forest, I saw a Gila woodpecker fly out from what I supposed was its nesting hole, about 15 feet up in a mesquite stub; the bird made such a great fuss about it that I felt sure that we had a set of woodpecker’s eggs within easy reach, and I called Mr. Willard to investigate it. He climbed the stub and chopped out the hole, while the woodpecker was flying about, scolding us and showing the greatest concern. But, much to our surprise, he pulled out an elf owl and three unmistakable elf owl’s eggs. I killed the owl and shot the woodpecker, which still seemed much interested; and, on skinning and sexing both specimens, I found that the woodpecker was a male and the owl a female. We were naturally much puzzled to figure out the relationship between the two birds and their interest in the nest. But, since reading Mr. Gilman’s remarks, quoted above, that sometimes the woodpecker’s tenants “do not even await the pleasure of the excavators, but take forcible possession,” it has occurred to me that probably this was a case in point. The owl may have appropriated the finished burrow of the woodpecker, and the latter was trying to evict an unwelcome tenant.
The remaining four nests found in this vicinity, and one found by Mr. Willard on June 11, were all in saguaros on the desert mesa; the heights from the ground varied from 16 to 20 feet; and the cavities varied in depths from 15 to 20 inches; there was one set of five eggs, two nests held four and one three eggs; and in one nest were two young and an addled egg.
Referring to the nesting habits of this woodpecker in the vicinity of the Gila River, in Arizona, Mr. Gilman (1915) writes:
Nesting sites in this locality are restricted to giant cactus (Cereus giganteus), cottonwood and willow, as they are the only suitable material for a nest excavation. More nests are found in the giant cactus, as these plants are more numerous than the others, and more “peckable,” though the willows and cottonwoods along the river and the canals are well patronized when sufficiently decayed. Of the nests I examined I should say that fifty per cent were in the cactus, and the rest equally divided between the other trees mentioned. * * *
As to the size of the holes in the cactus as compared with those in cottonwood and willow, I found no appreciable difference. I expected the holes in the cactus to average a little larger owing to possible greater ease in excavating but the difference was too slight to be sure of in measuring. Of eighteen holes measured, the average diameter was 1.95 inches; the largest was 2.25 inches and the smallest 1.87 inches. The deepest hole was 16 inches, with the entrance 2 inches in diameter. The shallowest one was 9 inches, with entrance a little less than 2 inches in diameter. The average depth of holes measured was a little more than 12 inches. Many of the holes were not exactly circular, there being a difference of from ⅛ to nearly ½ inch between the long and short diameter if it be allowable to use the term in that way. Usually the nest hole runs straight in for a short distance before turning downward, the distance seemingly depending on the texture of the wood. In one case the hole went straight back for nine inches before turning downward. It was in a big cottonwood stump, and the bird excavated horizontally until decayed wood was reached, when the hole turned downward. This was an extreme case, as the depth horizontally is usually about three inches. In the giant cactus it varies according to the diameter of the trunk, the smaller the trunk the less distance before turning downward. * * *
The same nest hole is used more than one season, both in cactus and other locations. In 1913 I found a nest in a big cottonwood stump containing young. The next year it had young again, and I cut into it to measure the hole and count them.