Hence one can say now that both Corvus brachyrhynchos brachyrhynchos and Corvus brachyrhynchos hesperis are to be included in future lists of Colorado birds.
The common Crow is normally a bird of moderately large and fairly dense timber, a growth found in Colorado only along the larger streams and in the mountains; if one plot the Crow stations of Colorado on a map, it at once becomes patent that most, if not all, of these stations are to be found along the courses and headwaters of the State’s larger streams. This fact seems to lend color and support to the idea that subspecies brachyrhynchos probably penetrated Colorado from the east by following the larger streams towards the mountains, for it is along these rivers that one finds trees to the Crow’s liking, and too, Crows are increasingly more common as one travels eastward along these watercourses. It would seem reasonable to believe that along similar natural “crow” highways hesperis would find its way eastward from the Pacific side into Colorado.
The smaller size, alone, of hesperis, often makes it distinguishable in the field, a fact which first came to my attention while in the “hills” on the Gila River in New Mexico, in 1906. During the same year I saw a considerable flock of Crows immediately south of Antonito, Colorado; I was then again impressed by the smaller size of these southern Colorado and New Mexico Crows. I now believe these Antonito Crows were subspecies hesperis; Antonito is on (or very close) to the Rio Grande River, which drains part of the Atlantic-Gulf of Mexico watershed, part of which watershed forms the western portion of Texas, an area included in the present known range of hesperis. It does not seem unreasonable to believe that hesperis works its way from western Texas, up along the Rio Grande, finally reaching the vicinity of Antonito, and also the San Luis Valley. In support of this latter view I am permitted to say that Mrs. Jesse Stevenson of Monte Vista, Colorado, recently saw a Crow for the first time in twenty-five years in this valley, and was at once impressed with its small size as compared with those she formerly studied in the East.
As mentioned above, it is clear that hesperis occurs on both sides of the Rocky Mountains in Colorado. Now one must ask if subspecies brachyrhynchos occurs on the western slope as well as on the eastern slope.
I cannot even inferentially decide whether or not subspecies brachyrhynchos reaches the west side of the Rockies in Colorado; there is but one reference to it in literature, known to me, as occurring on the western slope of Colorado, to-wit, that by Warren (20) who listed the Crows of Gunnison County as subspecies brachyrhynchos, doing it, however, as a matter of expediency only, as he took no specimens. If this subspecies does range to the west side of the Rocky Mountains in Colorado, I believe it will be found in northwestern Colorado, coming in as a straggler from Wyoming. Records of the Crow from northwestern Colorado and southwestern Wyoming are lacking (21), or at least unknown to me.
One can hazard the guess that the Crows of southeastern Colorado are subspecies brachyrhynchos, but hesperis may also be found in that area, coming in as an infiltration from Texas. I am convinced that hesperis works its way up from the Lower Rio Grande Valley, along the eastern foothills, finally reaching, as we now know, as far north as Weld County.
It is highly desirable that a considerable series of Crow skins be collected from Colorado, embracing specimens especially from the western portions of the State, and also from the southern border, to the end that the exact distribution of subspecies brachyrhynchos and hesperis be definitely delimited for Colorado.
Résumé.
I.—It can now be said categorically that the Crow occurs in Colorado in the guise of two subspecies, viz., brachyrhynchos and hesperis, both being found on the eastern slope, and only the latter on the western slope of the Rocky Mountains.
II.—The above conclusion stands if my determinations of the skins I have studied be correct; if my determinations be incorrect they show that the criteria by which these two subspecies are differentiated, are too subtile and refined for an ordinary ornithologist like myself to grasp and apply, or that the described differences between these two subspecies break down with the Crows found in Weld County.