Part 4

Relationships

The large genus Coluber is much in need of revision. Its many species, perhaps more than a score in all, occur in North America from southern Canada south to Guatemala, in eastern and southwestern Asia, in southern Europe, and in North Africa. All are active, slender-bodied snakes having smooth scales in few rows, and having large eyes with well developed vision. The North American species fall into two natural groups, the typical racers, and the whip snakes, often assigned to a separate genus, Masticophis (Ortenburger, 1928). The whip snakes are more specialized than the typical racers in having the eyes more enlarged, and the body form more slender and attenuate, with number of scale rows more reduced. The racers of the Old World are more diverse. Inger and Clark (1943) suggested a partitioning of the genus Coluber on the basis of the pattern by which scale rows are reduced, from the maximum number on the forebody to the minimum number at the posterior end of the body, supplemented by certain characters of the hemipenis and of the cephalic scutellation. Besides Coluber and Masticophis these authors recognized within the group the genus Platyceps with several species in southern Europe and southwestern Asia; Zamenis with several species in the same region and in North Africa, and Haemorrhois, a monotypic genus of Spain, North Africa and several Mediterranean islands. Although apparently valid in principle, this arrangement has not been generally followed.

Exclusive of those species groups whose assignment to the genus Coluber are somewhat questionable, the remaining species in the genus are: C. constrictor occurring throughout most of the United States and south along a narrow Atlantic coastal strip of Mexico to Guatemala; C. oaxacae of southern Mexico; and C. spinalis of northern China. C. oaxacae is poorly known as only a few specimens have been collected, but seemingly it is a near relative and derivative of C. constrictor, especially of that species' southernmost population. C. spinalis is much more distinct, as might be expected from its geographical remoteness. It is a slender, active snake, of olive coloration dorsally with 17 scale rows and a bright yellow, black-edged dorsal stripe and yellow ventral surface. It is relatively small (up to 755 millimeters snout-vent length) and is partial to riparian habitats but is also found in forests and in dry and barren regions (Pope, 1935:224-226). It is known to feed upon lizards.

Range

The common racer has been recorded in each of the 48 states of the mainland of the United States, also in New Brunswick, Nova Scotia, southern British Columbia, and southward through Mexico where it is limited to a narrow strip of east coast lowlands but extends as far as Guatemala. C. c. constrictor occupies the northeastern states and extends south into the Appalachian and Piedmont. C. c. priapus with its associated races paludicola, helvigularis, and anthicus has an Austroriparian distribution, occupying the Atlantic Coastal plain and the Gulf Region, and extending north in the Mississippi Valley to southern Illinois and Indiana. C. c. paludicola is localized with two disjunct populations--in the Everglades and on Cape Canaveral, Florida. C. c. helvigularis is even more restricted in range and is known only from the Appalachicola region of the Florida Panhandle and the adjacent corners of Alabama and Georgia. C. c. anthicus occupies much of central and western Louisiana and adjacent Texas. C. c. flaviventris occurs throughout the Great Plains, east in the "Prairie Peninsula" through Michigan and northern Ohio and west to the Rocky Mountains. C. c. stejnegerianus occurs from Matagorda Bay in Texas southward through eastern Mexico, with a seemingly isolated population in the Sierra del Carmen region of northern Coahulia. C. c. mormon occurs in the Pacific Coast states and Great Basin.

Actually, the range limits and the continuity of distribution within the area outlined are still poorly known. The species has not been recorded from the northern parts of Maine, Vermont, New Hampshire, Michigan, Wisconsin, or Minnesota, nor from northeastern New York. It is generally absent from southwestern desert areas. Records are particularly scarce and scattered in the Rocky Mountain states, suggesting that the distribution in this area may be discontinuous. In a large area comprising all of New Mexico and Arizona, the western half of Colorado, and the southern halves of Utah and Nevada, records are so scarce as to indicate that the species is there represented by only a few well isolated relict colonies. The type locality of mormon is "Valley of the Great Salt Lake," and there are numerous records from the northern part of Utah east of Great Salt Lake (Woodbury, 1931:75), but a record from Moab is the only one known to me from the southern half of the state. The only records from western Colorado are from three miles east of Fruita and two miles west of Grand Junction, Mesa County (Maslin, 1959:56). Apparently the only valid record from Arizona is that of Shannon (1950:59) from Eagar, Apache County, in the east-central part. Shannon also recorded the racer from Boulder Dam in extreme southern Nevada. Brattstrom (1955:152) has recorded the species from the lower Pleistocene of southeastern Arizona (Curtis Ranch), bearing out the idea that the racer has partly withdrawn from a range formerly occupied in the Southwest at a time when cooler and moister climate prevailed. Other fossil occurrences are of late Pleistocene age--Vero Beach and Seminole, Florida (Brattstrom, 1953a:245) and, doubtfully, Rancho LaBrea, California (Brattstrom, 1953b:376). The range of mormon has been mapped (Wright and Wright, 1949:134) as extending east to south-central Montana on the basis of one specimen allocated on the basis of two characters. Otherwise the range of mormon seems to be entirely west of the Continental Divide, well separated from that of flaviventris by desert and mountain barriers. The conspecificity of mormon with the other subspecies needs to be more thoroughly investigated, and geographic variation within mormon also merits study.

Geographic Variation

The common racer and the several species of whip snakes (Masticophis) were revised by Ortenburger (1928). More recently with much larger series of specimens, Auffenberg (1955) again revised the classification of C. constrictor, but his study was concentrated in Florida and neighboring southeastern states with relatively little attention devoted to populations of the western and central United States. As the species occurs throughout most of the United States and south through the coastal lowlands of eastern Mexico to Guatemala, it is found over a wide range of environmental conditions. Various characters are subject to geographic variation, and some of them follow clines that are maintained over extensive areas. Such characters as the number of hemipenial spines, and the enlargement of one or more basal spines into hooks, the shape of the premaxillary bone, the number of maxillary teeth, the numbers of ventrals and caudals, color of eye, number of dorsal saddle-marks and of ventral spots in juveniles, and ratios of body proportions including tail length to total length have been used to characterize the subspecies.

Also important is the shade of coloration of adults. The subspecies constrictor, priapus and helvigularis that are characteristic of forested habitats in the eastern United States are black dorsally and have their ventral surfaces suffused to a large extent with dark or dusky coloring. Farther westward the ground color becomes progressively paler, greenish, grayish or light brown, and the ventral surface is yellow (white on the throat and neck). The same tendency appears in C. c. paludicola of the Everglades. The populations of arid climates in southern Texas and in the far western states are relatively pale colored. The species thus conforms to Gloger's Rule in changing from a pallid coloration in arid climates to a dark pattern with eumelanins predominating in a humid climate.

Perhaps the most important character that is subject to geographic variation in the racer, and certainly one of the most neglected, is body size. With information now available it is not possible to compare the sizes of different populations except in a general way. The best sources of information concerning size in several subspecies other than flaviventris, are the publications of Auffenberg (1949 and 1955). Comparison of these data with my own is not entirely satisfactory because Auffenberg did not indicate clearly differences in size between the sexes, nor indicate the boundary line between young and adults. Also, his measurements are of overall length. For the purpose of comparison I have subtracted 22.5 per cent, an approximation of ratio of average tail length, from Auffenberg's figures. He stated (1955:98) that the series of specimens on which measurements were based were those "with a uniform coloration," that is to say they had lost the juvenal pattern and were probably sexually mature. Whether the same statement applied to the large series of stejnegerianus in the same author's earlier paper (1949:55) is doubtful.

C. c. constrictor: 34 New York specimens averaged 806 millimeters (Auffenberg, 1955:96).

C. c. flaviventris: 100 Kansas specimens averaged 791 millimeters (males, 746; females, 836).

C. c. priapus: 171 Florida specimens averaged 713 millimeters (Auffenberg, 1955:96).

C. c. stejnegerianus: 291 Texas specimens averaged 664 millimeters (Auffenberg, 1949:54).

C. c. mormon: 94 West Coast specimens (Museum of Vertebrate Zoology) averaged 563 millimeters (males 515, females 600).

C. c. anthicus: 35 northern Louisiana specimens estimated to average 582 millimeters (Clark, 1949:249--the author did not present individual measurements, but indicated the numbers in several size groups in his sample).

The 100 flaviventris in the above list were recorded in June, July and August, a season when the young of the preceding year are still small, and these young were not included. In a fall sample 63 males averaged 729 millimeters and 65 females averaged 886 millimeters, but with the nearly grown young (44 males and 40 females) included, the averages were changed to 651 and 768 respectively. Maximum length perhaps express differences between the subspecies as well as, or even better than, the averages listed above. The following figures indicate some of the maximum overall length measurements in inches that have been published by various authors. These measurements pertain to females unless otherwise indicated.

C. c. constrictor: 74-3/4, 74-1/4, 73, 65-1/2 (Auffenberg, 1955:96).

C. c. flaviventris: 71 (Pope, 1944:172), 72 (Conant, 1958:147).

C. c. priapus: 52-1/2 () (Auffenberg, 1955:98).

C. c. stejnegerianus: 37 (Auffenberg, 1949:54), 40 (Conant, 1958:148).

C. c. mormon: 51-1/2 (Museum of Vertebrate Zoology).

C. c. anthicus: 70 (Conant, 1958:149).

In my own study, the largest racers recorded from the Reservation and Rockefeller Tract had the following overall lengths: 59, 57-1/4, 55-1/2, 58 (projected from stub tail).

These sets of figures show that compared with the blue racer in Kansas, with which my own study was concerned, the black racer of the northeastern states reaches a larger size, while the racers of the Southeast and especially those of the far West and of southern Texas, are dwarfed. These size differences are almost certainly correlated with behavioral and ecological differences among the snakes involved. Adaptations to exploit certain types of prey and to utilize most efficiently certain habitats and types of cover, have led to divergent trends in different parts of the range.

Habitat

The racer dwells primarily in open situations, but as might be expected from its extensive geographic range, bringing it under the influence of diverse climates and habitats, its populations have diverged somewhat in adaptation to different environmental conditions. The eastern blacksnakes (subspecies constrictor and priapus) seem to prefer woodland and forest edge. In central Louisiana, anthicus occurs chiefly in an open type of woodland. The subspecies stejnegerianus is found chiefly in brushland and thorn forest. The western mormon is found in varied habitats, including moist streamside meadows, and chaparral. Published statements of herpetologists, based upon studies in limited areas, are briefly quoted below to show the trend of geographic change.

C. c. constrictor: This snake "occurs chiefly in fields" (Atkinson, 1901:148; Pennsylvania); "in more or less wooded regions and along hillsides and among bushes" (Surface, 1906:167, in Pennsylvania); "abundant, especially in wooded regions" (Hibbard, 1936:28, in Kentucky); "dry and more or less open places" (Conant, 1938:52, in Ohio); "old fields and areas about buildings" (King, 1939:572, in Tennessee).