Part 15

Attempts to census blue racers on the study plots, from the capture-recapture ratios, yielded highly variable figures for different areas and even for the same area at different times. Variability is believed to result mostly from the small sizes of the samples, none of which is large enough to yield a census figure that is statistically reliable. Combined samples yielded figures indicating populations of one to three adults per acre in early summer in areas of favorable habitat. To represent the entire population in late summer--the time of its annual maximum--these figures would need to be approximately tripled.

The blue racer depends mostly on speed to escape its enemies. In escaping it often takes advantage of a downhill slope to increase its speed. A racer startled at close range often sets out with a violent thrashing that attracts attention to a given spot, then glides away so silently and rapidly that its course is not detected. The snake may circle back and approach the scene of disturbance slowly and stealthily, from the direction opposite to that taken in departing. Often a racer seeks concealment by climbing into a bush or tree, and occasionally escape is effected by swimming. A racer that is caught or cornered usually makes a spirited defense by striking and biting. An alternative reaction, seen most typically when the snake is handicapped by injury or by low temperature, is to coil with the head concealed, and, with writhing movements, to smear the surface of the body with musk discharged from glands in the base of the tail.

Many natural enemies prey upon the racer, but in the present study the majority of records pertained to the red-tailed hawk. The broad-winged hawk, marsh hawk, red-shouldered hawk, sparrow hawk, and barn owl also are among the raptors that feed on this kind of snake. Among mammals the striped skunk is the only species definitely recorded to prey on the racer, feeding on the eggs as well as upon the young and adults. The common king snake, prairie king snake, timber rattlesnake, copperhead, and even the slender glass lizard have been recorded to prey on the blue racer, but probably all are of minor importance as natural enemies. Shrews (Blarina, Cryptotis) and mice (Peromyscus, Reithrodontomys) have sometimes killed and eaten racers confined in traps, and under natural conditions they possibly prey upon snakes that are immobilized when torpid from cold, in their hibernacula and temporary shelters. Chiggers are the most common ectoparasites of the racers. Four species of the chigger genus Trombicula have been recorded on racers from the Reservation. The racer is an important host of the common pest chigger, Trombicula alfreddugèsi, which often attacks humans. Most adult racers on the Reservation and nearby areas carry the fluke, Neorenifer lateriporus. In spring these flukes are conspicuous in the mouths of the racers, but in late summer they are not in evidence.

Literature Cited

Allen, M. J.

1932. A survey of the amphibians and reptiles of Harrison County, Mississippi. Amer. Mus. Novit., 542:11-12.

Anderson, P.

1942. Amphibians and reptiles of Jackson County, Missouri. Bull. Chicago Acad. Sci., 6:203-220.

Atkinson, D. A.

1951. The reptiles of Allegheny County, Pa. Ann. Carnegie Mus., 1:145-157.

Auffenberg, W.

1949. The racer, Coluber constrictor stejnegerianus in Texas. Herpetologica, 5:53-58.

1955. A reconsideration of the racer, Coluber constrictor, in eastern United States. Tulane Studies in Zool., 2(6):89-155.

Barbour, R. W.

1950. The reptiles of Big Black Mountain, Harlan County, Kentucky. Copeia, 1950:100-107.

Baxter, G. T.

1947. The amphibians and reptiles of Wyoming. Wyoming Wild Life, August and October 1947:1-8.

Blair, W. F.

1960. The rusty lizard. Univ. Texas Press, Austin, xvi + 185 pp.

Blanchard, F. N. and Blanchard, F. C.

1942. Mating of the garter snake, Thamnophis sirtalis sirtalis (Linnaeus). Papers Michigan Acad. Sci. Arts and Letters, 27:215-234.

Blanchard, F. N. and Finster, E. B.

1933. A method of marking living snakes for future recognition with a discussion of some problems and results. Ecology, 14:334-349.

Bogert, C. M. and Cowles, R. B.

1947. Moisture loss in relation to habitat selection in some Floridian reptiles. Results of the Archbold Expeditions, No. 58; Amer. Mus. Novit., 1358:1-34.

Bonn, E. W. and McCarley, W. H.

1953. The amphibians and reptiles of the Lake Texoma area. Texas Jour. Sci., 1953(4):465-471.

Boyer, D. A. and Heinze, A. A.