Further Observations on Variation in Canyon Wrens

Abstract

The Canyon Wrens (Catherpes mexicanus) of the western United States have proved to be a most troublesome group with respect to racial taxonomy. Great amplitude of individual variation in any one population coupled with small series of available specimens are the sources of difficulty. The two most careful considerations of this problem of variation in recent years appear to have been those of Grinnell and Behle (Condor, 37, 1935:247-251) and Behle (Bull. Univ. Utah, 34, 1943:56-67) in which, however, opposing nomenclatural representations of geographic variation were advocated. The later paper of Behle, based on some new material, particularly from Utah, portrays a pattern of variation which my current review of the group largely confirms. In brief, the wrens from California west of the Sierra Nevada are usually rich, dark brown dorsally. In the Great Basin and in the southern deserts coloration is exceedingly variable, with many paler, tawnyor gray-backed birds appearing. Apparently, as Behle has reported, in eastern Nevada and Utah pale and tawny, rather than rich brown, coloration predominates; I am not prepared to say from personal observation that this type of coloration is uniform there. In Colorado and Arizona, richly brown birds again appear, many of them like those of coastal California. Behle has stated that along the eastern escarpment of the Sierra Nevada the separation of the dark and pale birds is rather abrupt. This I think is something of an exaggeration. Recently I have taken samples from the Inyo district east of the Sierra and from the western Sierran slopes and western California, including some new material from San Luis Obispo County, and have mixed seasonally comparable material to test the feasibility of separating geographic groups on the basis of color. I find that only about three-fifths of the total of 60 specimens can be correctly separated by this means; there seem to be no other useful characters available. Behle (1943) advocated use of names for the extremes of color differentiation, namely the rich brown type in western California and the pale type in Utah, recognizing that there is a zone of intergrades or of mixed-type birds of great magnitude between them which occupies much more ground than do the extreme populations. This would be a reasonable proposal were it not for other complications. But mixed groups occur across the northern Great Basin (see beyond), not in a line of intergradation between California and Utah, and similarly to the southward in the deserts of California and in Arizona, and again to the east of Utah. Moreover we are not yet in a position to define the geographic limits of the uniform pale population in Utah and we certainly are not able to define an area where the rich-brown bird predominates on the west coast; such a color type is not uniformly present there. Some further nomenclatural difficulties arise in the application of existing names. Punctulatus (Ridgway, Proc. U. S. Nat. Mus., 5, 1882:343) would be available, as in the past, for the birds of coastal California, but conspersus (Ridgway, Amer. Nat., 7, 1873:603) is dubiously applicable to the pale tawny birds of Utah. The type of conspersus according to Behle, who has examined it, is a pale tawny bird like those of Utah. Yet this name should probably not be used for the Utah extreme as Behle has done in disregard for the population of western Nevada, of which the type was a part, and which is a mixed sort of population, representing a mid-segment of the color gradation between California and Utah. As shown by the trial sorting already reported, birds east (conspersus) and west (punctulatus) of the Sierran crest are not separable in large enough degree to make nomenclatural distinction of them useful. Problems similar to