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Part 11

Natural History of the Racer Coluber Constrictor · Henry S. Fitch — chapter 11 of 27 · ~3,984 words · public domain

Table 13. Growth of Racers Marked at an Age of Less Than One Year and Recaptured in Their Second, Third or Fourth Years

Column headings: A: Snout-vent length in mm. B: Weight in grams C: Probable age in months

====+=================================+================================== | Original record | Record(s) of recapture Sex +---------------+-----+----+------+--------------+-----+-----+------- | Date | A | B | C | Date | A | B | C ----+---------------+-----+----+------+--------------+-----+-----+------- | Nov. 12, 1952 | 342 |....| 2-1/2| May 20, 1955 | 702 | 110 | 33 | Nov. 1, 1953 | 330 | 11 | 2 | Aug. 16, 1956| 780 | 162 | 35-1/2 | Nov. 12, 1953 | 293 |....| 2-1/2| May 14, 1956 | 634 | 96 | 32-1/2 | | | | | Oct. 13, 1956| 689 | 110 | 37-1/2 | April 15, 1955| 320 | 13 | 9-1/2| June 8, 1958 | 740 | 118 | 45 | Oct. 2, 1955 | 348 | 18 | 1 | May 22, 1958 | 728 | 120 | 33 | | | | | May 21, 1960 | 795 | 130 | 57 | June 25, 1959 | 378 | 10 | 10 | June 30, 1960| 590 | 60 | 22 | | | | | June 7, 1961 | 705 | 123 | 33 | Nov. 1, 1953 | 330 | 11 | 2 | Aug. 25, 1957| 805 | 183 | 48 ----+---------------+-----+----+------+--------------+-----+-----+-------

Unlike young of the year, racers in their second autumn were trapped in large numbers. By this time all were large enough to be caught in the traps of quarter-inch wire mesh, and they were the most abundant size group. Many that were marked at this stage were recaptured after intervals of months or years, showing the trend of growth. Some of these snakes in their second autumn already had overtaken the more retarded third-year individuals. The two age classes cannot be separated with certainty. Selected records of individuals that were almost certainly second-year young at the time they were marked are presented in Table 14.

Table 14. Growth of Young Racers That Were Marked Near the Time of Their Second Hibernation

Column headings: A: Snout-vent length in mm. B: Weight in grams C: Probable age in months

====+==================================+==================================== | Original record | Record(s) of recapture Sex +--------------+-----+-----+-------+---------------+-----+------+------- | Date | A | B | C | Date | A | B | C ----+--------------+-----+-----+-------+---------------+-----+------+------- | Oct. 6, 1960 | 595 | 80 | 13 | July 23, 1961 | 650 | 70 | 23 | Oct. 13, 1950| 525 | 52.6| 13-1/2| Oct. 2, 1951 | 675 | 105 | 25 | Nov. 2, 1950 | 545 | 55.6| 14 | Oct. 24, 1951 | 670 | 100 | 26 | Sept. 2, 1957| 522 | 57 | 12 | Oct. 14, 1958 | 690 | 103 | 25-1/2 | Oct. 17, 1953| 558 | 47 | 13-1/2| May 10, 1955 | 718 | .... | 32 | Nov. 14, 1956| 587 | 57 | 14-1/2| May 20, 1958 | 728 | 100 | 52-1/2 | | | | | June 17, 1959 | 880 | 219 | 64-1/2 | Sept. 7, 1959| 533 | 45 | 12 | June 6, 1961 | 740 | 112 | 33 | Oct. 17, 1959| 558 | 56 | 13-1/2| July 21, 1960 | 625 | 63 | 22-1/2 | | | | | June 7, 1961 | 670 | 95 | 33 | Oct. 16, 1952| 577 | 62.0| 13-1/2| May 31, 1955 | 809 | 160 | 45 | | | | | May 11, 1956 | 855 | 144.3| 56-1/2 | Oct. 11, 1950| 570 | 65.9| 13-1/2| July 11, 1956 | 820 | 193.6| 82-1/2 | Oct. 14, 1953| 560 | 52 | 13-1/2| June 29, 1958 | 794 | 256 | 70 | Oct. 6, 1950 | 563 | 55.8| 13 | Sept. 28, 1958| 907 | 243 | 109 | Oct. 14, 1953| 523 | 44 | 13-1/2| May 19, 1959 | 818 | 190 | 80-1/2 | | | | | May 17, 1960 | 850 | 211 | 92-1/2 | Oct. 13, 1953| 521 | 50.1| 13-1/2| May 13, 1958 | 814 | 166.4| 44-1/2 | | | | | June 3, 1959 | 826 | 165 | 47 | Nov. 5, 1953 | 512 | 34 | 14 | May 22, 1958 | 847 | 135 | 69 | Aug. 11, 1953| 534 | 39.2| 11-1/2| Sept. 18, 1954| 670 | 143 | 24-1/2 | Oct. 14, 1949| 588 | 55.2| 13-1/2| Oct. 11, 1950 | 713 | 114.0| 25-1/2 | Oct. 6, 1950 | 570 | 60.4| 13 | Oct. 11, 1951 | 783 | 174 | 25-1/2 | Oct. 31, 1953| 582 | 58 | 14 | Oct. 5, 1954 | 860 | 195 | 25 | Oct. 21, 1959| 588 | 63 | 13-1/2| May 7, 1961 | 730 | 120 | 32 | May 14, 1960 | 506 | 34 | 20-1/2| Oct. 26, 1960 | 690 | 90 | 26 | Oct. 22, 1960| 527 | 45 | 13-1/2| Oct. 7, 1961 | 620 | 74 | 25 | May 3, 1960 | 530 | 48 | 20 | May 16, 1961 | 700 | 110 | 32-1/2 | May 27, 1961 | 535 | 40 | 21 | Oct. 25, 1961 | 672 | 98 | 26 ----+--------------+-----+-----+-------+---------------+-----+------+-------

From the records in Table 14 and many more like them, average and extreme sizes for progressively older age groups were estimated. Even racers that were already of adult size when they were marked were tentatively identified with one or another age group, and their records of subsequent growth were used. Most of the records show that the females grow more rapidly than the males, and are, on the average, larger at any given age.

Relatively few individual racers were recaptured after periods of several years. Each of the eight listed in Table 15 is among those that were captured in four or more different years, and their records are significant in revealing the trend of growth after sexual maturity has been attained. These snakes, one to three years old at the time they were marked, show well the persistent but decreasing growth, and the fluctuating weight that is characteristic of this and other species.

Some of the largest racers recorded had already reached unusually large size when they were first captured, so there was no opportunity to determine their ages. Several others, originally captured as small- or medium-sized adults, subsequently grew to a size approaching the maximum, and thus provided a basis for estimating the ages of large individuals. The records of nine such racers are listed in Table 16.

Table 15. Changes in Lengths and Weights in Eight Racers Recaptured Repeatedly Over Periods of Years

=====================+=============+=============+========+========== | Snout-vent | Tail length | Weight | Probable Date of Capture | length in | length in | in | age in | millimeters | millimeters | grams | months ---------------------+-------------+-------------+--------+---------- No. 1, male | | | | October 21, 1953 | 676 | 216 | 85 | 25-1/2 October 12, 1954 | 733 | 238 | 128 | 37-1/2 July 31, 1955 | 755 | 243 | 143 | 46 May 20, 1956 | 785 | 250 | 153 | 55-1/2 July 15, 1957 | 788 | 252 | 162 | 69-1/2 June 30, 1958 | 820 | 264 | 200 | 81 May 15, 1959 | 828 | 263 | 195 | 91-1/2 May 14, 1960 | 840 | 265 | 195 | 103-1/2 No. 2, male | | | | May 9, 1955 | 678 | 212 | 105 | 32 May 26, 1958 | 827 | 248 | 195 | 69 May 3, 1959 | 865 | 262 | 218 | 80 May 14, 1960 | 877 | 264 | 218 | 92-1/2 July 16, 1960 | 890 | 257 | 190 | 94-1/2 No. 3, male | | | | May 26, 1955 | 565 | 171 | 53 | 21 August 28, 1957 | 798 | 245 | 155 | 48 May 13, 1958 | 814 | 249 | 137 | 56-1/2 May 4, 1959 | 848 | 252 | 180 | 68 June 12, 1961 | 896 | 262 | 198 | 93-1/2 No. 4, male | | | | May 19, 1956 | 632 | 208 | 78 | 20-1/2 August 2, 1957 | 740 | 238 | 123 | 35 May 20, 1959 | 796 | 246 | 132 | 56-1/2 May 23, 1960 | 813 | 280 | 140 | 68-1/2 No. 5, male | | | | June 30, 1956 | 594 | 188 | 73 | 22 October 12, 1956 | 658 | 200 | 80 | 27-1/2 July 14, 1957 | 690 | 220 | 102 | 34-1/2 June 23, 1958 | 749 | 226 | 136 | 46 July 24, 1959 | 751 | 239 | 133 | 59 May 27, 1960 | 765 | 235 | 130 | 69 No. 6, male | | | | October 19, 1956 | 518 | 167 | 43 | 13-1/2 July 19, 1957 | 673 | 218 | 96 | 22-1/2 May 5, 1960 | 780 | 250 | 175 | 56 May 9, 1961 | 840 | 272 | 272 | 68 No. 7, female | | | | May 12, 1957 | 790 | 238 | 175 | 32-1/2 September 3, 1957 | 810 | 243 | 208 | 36 October 1, 1958 | 883 | 259 | 206 | 49 July 11, 1959 | 915 | 247 | 190 | 58-1/2 September 12, 1960 | 930 | 249 | 238 | 72-1/2 September 14, 1961 | 1012 | 268 | 332 | 84-1/2 No. 8, female | | | | June 23, 1955 | 601 | 175 | 67 | 22 August 3, 1958 | 920 | 255 | 300 | 60 July 23, 1959 | 955 | 281 | 211 | 71 May 18, 1960 | 962 | 262 | 260 | 81 ---------------------+-------------+-------------+--------+---------- Incomplete. With food.

A few adult racers recaptured, including different individuals of small, medium, and large size, failed to make any measurable gain in length over periods of months, or even over several years. Most often the large individuals were those that failed to grow or made only slight gains. Some of the snakes that failed to increase in length suffered dramatic weight losses, perhaps as a result of injury, disease, or parasitism. However, other individuals that failed to gain appreciably in length did gain in weight. Doubtless both genetic and environmental factors were involved. A few racers gave the impression of being stunted by adversity. All records obtained of growth (or failure to grow), throughout the period of my study were used in compiling Table 17.

Table 16. Growth in Several Racers That Were Already Adult When Originally Captured and That Subsequently Attained Unusually Large Size

Column headings: A: Snout-vent length in mm. B: Weight in grams C: Probable age in months

Mortality Factors and Adaptations for Survival

Defense, and Escape

The behavior patterns that are associated with defense and escape in snakes are widespread. The common racer is typical of the more generalized snakes. Almost all elements of the racer's behavior are found in snakes of other genera and perhaps, of other families. The racer differs from these only in minor details of its behavior, in the circumstances under which various behavioral traits are elicited, and their relative importance. The common racer is one of the swiftest of North American snakes, and it usually depends upon speed to avoid enemies. Racers crossing roads may detect approaching automobiles at a distance, and thereby may be stimulated to accelerate their movements and so escape onto the shoulders rather than becoming traffic casualties as many individuals of most other kinds of snakes do under the same circumstances. The chances of such escape are of course much better on dirt roads that are relatively narrow and have a rough surface permitting efficient traction, than on wide smooth, paved highways. The snakes are somewhat reluctant to venture onto open expanses of pavement.

Table 17. Sizes of Racers of Different Age Groups in May and October

========+==================================================== | Males +-------------------------------+-------------------- Age in | Snout-vent length in mm. | Weight in grams Years +---------+----------+----------+---------+---------- | | Typical | Observed | | Observed | Average | range | range | Average | range --------+---------+----------+----------+---------+---------- 1+ | 539 | 432-609 | | | 2- | 615 | 500-676 | 560-674 | 68.2 | 51-92 2+ | 668 | 610-700 | 620-710 | 107.4 | 63-134 3- | 706 | 677-730 | 648-755 | 102.1 | 65-129 3+ | 740 | 701-754 | 667-780 | 147.0 | 93-216 4- | 757 | 731-772 | 725-809 | 139 | 95-251 4+ | 785 | 755-793 | 720-850 | 167.4 | 128-225 5- | 805.5 | 773-810 | 743-855 | 152.4 | 110-198 5+ | 810 | 801-831 | 773-858 | 163.9 | 89-211 6- | 827 | 811-831 | 765-883 | 175.9 | 130-230 7- | 845 | 832-850 | 788-900 | 181.2 | 125-210 8- | 868 | 851-873 | 740-890 | 217.5 | 194-225 8+ | 870 | 861-884 | | | --------+---------+----------+----------+---------+---------- | Females +---------+----------+----------+---------+---------- 1+ | 581 | | 415-658 | | 2- | 644 | 520-739 | 580-738 | 83.5 | 52-127 2+ | 743 | 685-804 | 670-826 | 135.2 | 73-200 3- | 810 | 740-829 | 730-880 | 149.4 | 98-219 3+ | 836 | 804-869 | 736-915 | 181.2 | 120-268 4- | 866 | 830-880 | 791-920 | 212.3 | 175-243 4+ | 883 | 870-914 | 810-952 | 191.2 | 143-300 5- | 914 | 880-929 | 833-1088 | 209.6 | 136-275 5+ | 932 | 915-954 | 883-990 | 250.4 | 195-336 6- | 965 | 930-961 | 892-1020 | 245.9 | 218-283 6+ | 970 | 955-980 | 885-1003 | 271 | 243-336 7- | 974 | 962-990 | 919-1050 | 251.3 | 150-330 7+ | 1000 | 980-1015 | 930-1085 | 295.6 | 235-375 --------+---------+----------+----------+---------+----------

A racer suddenly startled by close approach of a human usually flees at high speed. The first part of its course, up to 20 feet or more, is marked by a violent lateral thrashing of the body and tail, which may help the snake to gain speed, but which seem chiefly designed to draw attention of a potential attacker to the spot that the snake is leaving. In any event, the mode of progression abruptly changes to a swifter and much smoother travel, and the snake may seem to vanish completely or as it glides rapidly away, its course may be marked by the slowly waving tops of tall grass. The trend of travel away from the site of disturbance is in an irregularly zig-zag course. The method of crawling, with lateral undulations of the body, supported against scattered pivot-points along the way, tends to prevent the snake from moving more than a short distance in a straight line.

In checking traps along hilltop rock ledges in October, I have often flushed racers that had come to the ledges searching for hibernation dens. In such an instance the startled racer would usually dart away down the steep slope at unusually high speed, and within a few seconds might have covered 100 feet or more, progressing with a minimum of lateral undulations, and seeming to flow or coast over the ground surface with scarcely any effort. Although coursing downhill in this manner provided an effective method of escape, racers startled at the ledges or on other sloping ground sometimes followed a course parallel to the ledge, or even turned uphill, with disastrous slowing. Often I have accomplished capture by hand, by the strategy of running downhill to get below the escaping snake, causing it to turn back up the slope, there to be slowed to the extent that it could be overtaken.

A racer that has been flushed, and has disappeared after creating a commotion by its violent thrashing, may, within a period of minutes, return surreptitiously to the vicinity, gliding back slowly and silently from the direction opposite that in which it departed. It may climb into a tree or bush where, lying stretched on outer twigs and concealed in dense foliage, it will sometimes permit close approach, rather than reveal its presence by moving. If too much disturbed however, such a snake will move away, higher, or to the opposite side of the clump, with a slow and stealthy gliding motion which is likely to escape detection. The sudden stops and abrupt changes in direction make it difficult to follow the course of a climbing racer, even though it is moving slowly. The tendency to climb to escape danger seems to be especially strong in the western subspecies, C. c. mormon. In my years of experience with the racers in the chaparral belt of western Oregon and California, I found that one of the most characteristic responses to danger was to climb into a bush or low tree and seek concealment in the thick foliage. In most instances the snake was from one to eight feet above the ground; usually it did not attempt to climb high in a tree even when there was opportunity to do so. The racer's prowess as a climber is limited. In thick brush where its weight is supported by numerous stiff twigs simultaneously, it is at home and can travel rapidly, but it cannot cling effectively to rough bark of a vertical tree trunk as can the rat snakes (Elaphe sp.) and others that are more specialized in their arboreal adaptations. Chaparral-type shrubs such as Ceanothus cuneatus and Arctostaphylos viscida were those in which western yellow-bellied racers were seen climbing most frequently. Crab-apple (Pyrus ioensis) and haw (Crataegus sp.) were the shrubs most frequently utilized by blue racers on the Reservation. Carr (1950:80) noted that Florida racers were much less given to tree-climbing than were those of more northern regions. C. c. stejnegerianus of southern Texas is reputed to have arboreal tendencies highly developed (Mulaik and Mulaik, 1942:14).

The racers kept in an outdoor enclosure in the summer of 1962 spent much of their time above the ground, climbing in several walnut saplings. Usually in the warmer part of the day three or four of the five racers in the pen were climbing. In the trees a racer usually lay extended or in a loose coil among foliage in the outer twigs, at a height of five to 12 feet. Such a snake might rest for hours in almost the same position. Racers do not ordinarily enter the water voluntarily, but they are swift and efficient swimmers when the need arises. On one occasion a large female, seen near the edge of the pond on the Reservation, and approached from the landward side, took to the water without hesitation and swam strongly to the opposite shore more than 100 feet away. Other observers have recorded similar incidents.

A racer that is suddenly startled at close range may make no attempt to escape, but instead may coil and perform slow writhing movements, with the head pressed to the ground and concealed beneath part of the body. Musk, exuding from the anus is spread over the body surface as the movements continue. Only a small percentage of the racers found free in their natural habitats reacted in the manner described. In each such instance, the circumstances were such that the racer was prevented from making its usual rapid getaway, either because temperature was unusually low for activity, or because the snake was away from suitable cover. After removal from a live-trap, with handling, and especially clipping of scales, racers were much more likely to behave in this passively defensive manner, which seemingly constitutes a second line of defense in snakes which have been prevented from escaping--either cornered, captured, or injured by a predator. The musk is creamlike in color and consistency, and is secreted from sausage-shaped glands in the base of the tail. Its odor is rather disagreeable, but less so than that of musks of various other genera. Also, it is less penetrating and lasting than many other musks. In handling the racers removed from traps I attempted to avoid being smeared with the musk by grasping the snake by the tail and neck and keeping its body stretched out. While the snake was being examined, and measured a droplet of musk would form at the anal orifice and would begin to flow down the snake's body. To avoid contact with the musk I would wipe away the droplet with a paper towel or leaf, but the musk droplet might be replaced several times within the few minutes that the snake was restrained.

A racer that is confronted with an object arousing its suspicion or indicating possible danger, may move away slowly with a characteristic "threat display." The forebody and neck are held rigid, well off the ground, and slightly arched, with the neck flattened in a vertical plane--causing this part of the snake to appear from lateral view larger than it actually is. The tongue is protruded frequently and waved slowly. A racer that has been disturbed and is trying to gain shelter in a direction that brings it closer to the danger usually will adopt this tense attitude, but a single threatening movement will cause it to abandon its circumspect pose, and panic in an attempt to reach the nearest shelter in the shortest possible time.

A common response to an alarm is to vibrate the tail. The tail being long and slender is vibrated much less rapidly than the short, muscular organ of a rattlesnake, or even the medium-short tail of a bull snake. The rapid twitching produces a characteristic sound in dry vegetation. A racer that vibrates its tail is fully active and aroused; the sound is heard as the snake pauses before it makes a dash for shelter. At times the sound probably functions as a decoy to distract the attention of potential predators, affording the racer an opportunity to escape.

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