HABITS
Harry S. Swarth (1917) is responsible for the recognition of this race, which seems to differ from the Williamson’s sapsucker of the Pacific coast in the same way that the northern white-headed woodpecker differs from the southern race of that species; he says:
The differences are as worthy of recognition in one case as in the other. It is my suggestion here that the Rocky Mountain race of the Williamson Sapsucker be separately recognized on the basis of its lesser bill measurements as compared with those of Sphyrapicus thyroideus thyroideus of the Pacific Coast.
As regards a name for this form, there is already one that seems to be clearly available for use. A specimen from Mexico was designated by Malherbe (Journ. für Orn., 1854, p. 171) as Picus nataliae, and an example from any part of Mexico (save possibly from the mountains of northern Lower California) would assuredly be of the Rocky Mountain subspecies. Also in the measurements given by Malherbe, length of bill (“du bec, du front 20 millimeters”) places his bird unequivocally with this race.
It is reasonably certain that in the Rocky Mountain region the species does not breed south of the Mogollon Divide, though it does occur as a common winter visitant in southern Arizona and over a large part of the Mexican plateau. These winter visitants, as shown by numerous specimens at hand, are migrants from the Rocky Mountain region to the northward, and not from the Pacific Coast region. So the name nataliae, as given by Malherbe to a Mexican specimen, can safely be used for the Rocky Mountain subspecies, which may therefore stand as Sphyrapicus thyroideus nataliae (Malherbe).
Mrs. Florence M. Bailey (1928), referring to the striking difference in plumage between the male and the female in this species, remarks:
The cause of this strongly contrasted sexual coloration unique among the woodpeckers of the United States is one of the unsolved problems of ornithology that stimulates speculation and so adds zest to the study. Is it, as Mr. Swarth suggests, that the female is still in a primitive stage of development? Correlating the brown coloration of the pasture-frequenting flickers with the ant-eating habits so marked in the Rocky Mountain sapsucker, it would seem that the color of the female might have been ancestrally adapted to a more open habitat than that in which the pair are found today; or has the ant-eating habit been diverted from ants that live on the ground in the open to those that live on tree trunks? The feeding habits of the anomalous pair should be carefully studied in the field.
Dr. Edgar A. Mearns (1890b) says that in Arizona it “breeds very commonly at the highest altitudes, frequenting the spruce and fir woods. It seldom descends far into the pine belt during the breeding season, although it is found in the pines in winter, occasionally descending even to the cedars in severe weather; and after the nesting season it frequently roves down to the pine woods with its young. When shot, it usually fastened its claws into the balsam bark and remained hanging there after life was extinct.”
Milton P. Skinner says in his Yellowstone Park notes: “In this Park, the Williamson sapsucker lives below 7,000 feet and prefers mixed forests of aspen and fir, but it is not particular whether in dense forest or in the borderland between forest and open.”
Spring.—Mr. Swarth (1904) witnessed a well-marked spring migration in the Huachuca Mountains, Ariz., of which he says: