A Systematic Review of the Mountain Chickadee

Jan., 1956 51 A SYSTEMATIC REVIEW OF THE MOUNTAIN CHICKADEE By WILLIAM H. BEHLE Chickadees of the species Parus gambeli have a range restricted to western North America where they occupy mountainous country from the Rocky Mountains west to the Cascade-Sierra Nevada cordillera and the interior coast ranges of California and south through the mountains of southern California to the Sierra San Pedro Martir and Sierra Juarez of northern Lower California. Mountain Chickadees are essentially resi- dent birds showing no pronounced migratory movements although some individuals move to lower elevatioas in fall and winter, and occasionally vagrants wander out of their breeding range. The habitat of the speciesis in general coniferous forest, where it breeds from the lowest altitudinal levels of this ecologic type up to timber line. Being widely distributed over a diversified geographic area and thus being subject to varying environmental influences, the species is composed of several populations of subspecific rank. However, the distinctness and geographic limits of some of these races have been in doubt. It has been the purpose of this study to analyze variation in the principal external characters of the species, determine more precisely the ranges of the races, inquire as to the degree of differentiation and the relationships of the subspecies, and thus to extend our knowledge of the evolution of the species. For the loan of comparative material which has made this study possible I am in- debted to A. M. Bailey, Denver Museum of Natural History; the late A. J. van Rossem, and Thomas R. Howell, Donald R. Dickey Collection, University of California at Los Angeles; Robert T. Orr, California Academy of Sciences; Alden H. Miller, Museum of Vertebrate Zoology; and John W. Aldrich and Herbert Friedmann, United States Na- tional Museum. The figures were prepared for publication by my colleague, W. W. Newby, to whom I express my appreciation. Acknowledgement also is made of aid in revision of manuscript and statistics by Robert K. Selander. METHODS Linear measurements were taken in millimeters as follows: chord of the wing; tail from point of insertion between the middle rectrices to the tip of the lbngest rectrix; length of bill from anterior edge of nostril to tip of the maxilla; depth of bill from anterior edge of nostril to lower edge of mandible in same transverse plane; and width of bill at base. In the course of the study the measuring of tarsal length and length of middle toe was discontinued becauseof generally unsatisfactory and insignificant results. Statistical analyses of the measurable characters are presented for each race in tabular form and comparisons are made graphically between the several races following the method described by Dice and Leraas (1936) as modified by Pitelka (1951) and Davis (1951). The samples for each race do not include intergrades but do include both breeding and winter birds taken within the range of the subspecies,since they are resi- dent. Only the measurements of postjuvenal specimens were used. Where the wing and tail feathers were badly worn they were not measured. Juveniles can be distinguished by their loose, fluffy feathers and abbreviated bills. In those few instances where imma- ture birds (as determined by skull condition) in first fall plumage were available, their average measurements did not vary from those of adults, nor did they differ from adults in plumage characters. In studying geographic variation in color characters, individual variation, seasonal effect of wear, and “foxing” of museum specimens had to be weighed before geographic variation could be appraised. Post-mortem browning does occur and the changes are 52 THE CONDOR Vol. 58 most noticeable on the rectrices and remiges. Old specimenshave lost the blue-gray tone that characterizes fresh specimens. While members of the family Paridae are prone to foxing to a greater degree than in many other families, I do not believe that Mountain Chickadees undergo such extreme post-mortem color change as Davis (1951:6) found in Brown Towhees. Some difficulties were presented where only old material of some . populations was available and so had to be compared with new material of others, These casesare noted in the text. Capitalized color designations follow Ridgway (1912). REVIEW OF PREVIOUS WORK The species was first described as Parus montanus by Gambel (1843: 259), based on a specimen taken about a day’s journey west of Santa Fe, New Mexico. The name Parus montanz~ was shown by Ridgway (in A.O.U. Committee, 1886:335) to be pre- occupied, and the name Parus gambeli was substituted. When Ridgway (1904:408) prepared the account for the Birds of North and Middle America no subspecieswere known, although his measurements suggestedthat geographic variation did exist in the characters measured. The species was called Penthestes gambeli at that time. A few years later the race baileyae was described from southern California by Grinnell (1908: 29). Grinnell (1918) later undertook a systematic revision of the species and at that time described two additional races, inyoensis from the desert mountains of eastern California and abbreviatus from northern California. The range of inyoensis was later found by Linsdale (1936:87) to extend throughout the Great Basin. The range of abbreviutus was extended by Oberholser (1919) to include Oregon, Washington, and central Idaho, and thence north to central western Alberta and northern British Colum- bia. However, van Rossem (1928) changed this concept of distribution when he described the subspeciesgrinnelli, with a range extending from east-central Oregon, eastern Washington and northern Idaho north through British Columbia. In the meantime Grinnell and Swarth (1926: 163) described stratus from the Sierra San Pedro Martir of Lower California. A detailed picture of the distribution of the several races occurring in California was presented by Grinnell and Miller (1944:300-303). In the present review I have had essentially the same material that Grinnell and Miller so carefully worked over. As a result little information is added for the California region and it is corrobo’rative of their findings. My major contribution has been to work out the picture of geographic variation in the populations farther east. In the course of this study the race wasatchensis was described (Behle, 1950), with a range covering central and southern Idaho, southwestern Wyoming and all of Utah except the mountains of the extreme eastern and western margins of the state. GEOGRAPHICALLY VARIABLE CHARACTERS Color of dorsum.-This is one of the most variable characters of the speciesand in some cases serves as the principal basis for distinction between races. It is correlated to some extent with flank and side coloration. A well-marked north-south cline exists in this character in populations from the Cascade-Sierra Nevada southward through the mountains of southern California to the Sierra San Pedro Martir of northern Lower California. The cline is toward increasing pigmentation or darker coloration to the south. Those examples representing the race abbreviatus are light gray. Those from the mountains of southern California representing baileyae are slightly darker, while those from the San Pedro Martir called stratus are still darker, representing the extreme of dark gray coloration. Jan., 1956 SYSTEMATICS OF MOUNTAIN CHICKADEES 53 In addition there is a west-east cline which extends from the gray color of the atratus-baileyae-abbreviatus group to a light buff or tan color of inyoensis of the Great Basin, through a darker gray-green form, wasatchensis,which occurs just east of the Great Basin, to the brown of gambeli of the Rocky Mountain region. A slightly differ- ent transition from the gray coloration of coastal birds to the brown of Rocky Mountain birds is seen through eastern Washington and northern Idaho, where the race grinnelli represents a transitional stage. Color of sides and flanks.-Accompanying the grayish dorsum of the coastal trio of races, abbreviatus-baileyae-stratus, the color of the sides and flanks is likewise gray and the same cline toward darker coloration to the south is manifest. In abbreviatus the flanks are tan-gray. In baileyae they are darker and dirty appearing but still tan-gray, while in atratus the flanks are still darker, more of a brown-gray. In the Rocky Moun- tain region (gambeli and grinnelli) the flanks are differently colored from the dorsum, being pinkish buff or cinnamomeous. Between these two areas a transition occurs so that the flanks of chickadees from the Great Basin and Utah mountains (inyoensis and wasatchensis) are buffy. In northwestern Nevada, however, the gray color of abbreviatus prevails. Farther north across eastern and central Washington a more erratic transition occurs. Some individuals with cinnamon colored flanks occur as far west as the east side of the Cascades.The blending of coastal gray and Rocky Mountain cinnamon is best seen in Okanogan County, Washington. Amount of white on head.-The prominence of the superciliary stripe and its extent posteriorly, together with the amount of white in the frontal stripe of the head, are subject to great individual variation and also to some geographic variation. In the race stratus of northern Lower California the white is greatly reduced, being narrower and not extending so far posteriorly. This was brought out in the statement of Grinnell and Swarth ( 1926: 163-164) made while comparing atratus and the neighboring race bail: eyae: “The white on the head of atratus is not only less in area occupied, but it is shal- lower; and birds in breeding plumage, when it ia [further] reduced or effaced by wear, come to bear a curious resemblance about the head to Penthestes [= Parus] atricapil- Ius.” The amount of white seemsto be fairly constant in the races baileyae, abbreviatus, grinnelli, gambeli and wasatchensis.The race inyoensishas the greatest amount of white, especially in examples from central northern Nevada.

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