♂. Wing, 6.40–7.00; tail, 3.00–3.30; culmen, .55–.60; tarsus, 1.50–1.70; middle toe, .80. (Smallest, No. 5,183, Fort Pierre, Nebraska; largest, No. 6,881, Sacramento, California.)
♀. Wing, 6.50–6.80; tail, 3.15–3.30; culmen, .51–.55; tarsus, 1.50–1.60; middle toe, .80. (Smallest, No. 45,020, Laredo, Texas; largest, No. 3,971, San José, Lower California.)
Juv. Upper surface earth-brown, as in the adult, but entirely uniform, except the wings and tail; upper tail-coverts, and a large oval patch on the wing (covering the middle coverts and the posterior half of the lesser-covert region), plain isabella-white; the anterior portion of the lesser-covert region darker brown than the back. Gular region well-defined pure white; jugular collar conspicuous and unspotted. Whole lower parts immaculate isabella-white.
Hab. Western Province of United States, from the Plains to the Pacific, and from the Rio Grande to Cape St. Lucas; Mexico.
Localities: Xalapa (Scl. 1857, 290); Texas (Dresser, Ibis, 1865, 330; resident).
Specimens never vary in the pattern of coloration, and but little in the relative amount of the brown and white spotting; the shade of the brown and the depth of the ochraceous tinge vary considerably, however, in different individuals,—but irrespective of locality,—the brown being paler and the white purer in summer than in fall and winter, after the new dress is freshly assumed. The brown on the breast varies considerably in quantity, being sometimes nearly uniform, thereby abruptly contrasting with the white jugular band, and again frequently with the brown hardly greater in amount than the white, the two colors being in regular bars, as on the sides and flanks.
There is certainly but one species, or even race, of Burrowing Owl in North America. This is represented in the Smithsonian collection by over fifty specimens, including examples from all parts of its range. Upon a close inspection of all the specimens in this extensive series, I was very much surprised to find so little variation; indeed, all the specimens are so much alike that a detailed description of the colors of one would answer for almost any individual. The shade of color varies mainly according to the age of the feathers, those newly acquired having a darkness of tint and a softness of texture not seen in those more worn (as in midsummer dress), which have a bleached or faded appearance. I fail entirely to detect the different styles of plumage which Mr. Cassin has described, and his diagnoses of two supposed species will not at all hold good when applied to specimens from either of the two regions which they were considered to characterize.
Examining critically the large series at my command, I find that the principal discrepancy among individuals is the amount of feathering on the tarsus; this extending to the toes was supposed to characterize the A. cunicularia of North America the habitat of which was considered as restricted in North America to the west of the Rocky Mountains (see Cassin, Birds of North America, as cited above); the nearly naked tarsus was believed to be characteristic of the A. hypogæa, as restricted, and the habitat assigned to this was “from the Mississippi River to the Rocky Mountains.” Now, dividing the series under examination into two sets, according to this feature, we have, first, cunicularia from the following localities: from the Rio Grande, all specimens but one; Tongue River, Montana; and Petaluma, Santa Clara, and San Francisco, California. Next, hypogæa represents the following localities, besides places within the range ascribed to it: Utah; Lower California, including Cape St. Lucas, all specimens; San Diego, California, several specimens; Santa Barbara, San Francisco, Sacramento, and Fort Tejon, California; and Tamaulipas, Mexico.
Though we have but one species or form in North America, the South American bird is different: this is the true cunicularia of Molina, and though not specifically distinct from our bird, is nevertheless an easily recognized geographical race. It is larger, the wing measuring from 7.00 to 7.50, instead of 6.40 to 7.00; the brown of the plumage is appreciably darker than that of most specimens of hypogæa, but less extended; on the outer web of the primaries the white spots are larger,—sometimes confluent along the edge,—and on their inner webs the white largely prevails, the dusky bars appearing only towards the ends; the outer tail-feather is almost wholly white, instead of having brown bars, broader than the white ones. Of the var. cunicularia there are eight specimens in the collection (chiefly from Paraguay, Buenos Ayres, and Chile), while numerous others, in various collections, have been examined besides. All the American forms of this subgenus seem clearly referrible to one species, as being at the most but geographical races.
Habits. The Burrowing Owl of North America inhabits the country between the Pacific coast and the Mississippi River, especially in the lower plains in Nebraska and in Kansas, as well as in particular districts in Utah, Arkansas, New Mexico, the Indian Territory, Texas, Arizona, California, and Mexico. They are usually very abundant, congregating together in large communities, and differing from most members of their family by living and breeding in burrows in the ground. Their habits are peculiar and interesting.