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.