Chapter 8 of 13 · 3750 words · ~19 min read

Part 8

On August 17, at 11:00 a. m., hatchlings no. 5 and no. 6 had lost their egg teeth. All others still had their egg teeth then, but by 10:00 p. m. that of no. 8 was missing, and that of no. 4 was loose and dropped out while the snake was being handled. On August 20 at 9:00 a. m., hatchling no. 7 had lost its egg tooth; nos. 2 and 3 retained theirs only in part, and no. 1 had its egg tooth intact. By noon on August 22 no trace of an egg tooth remained on any of the hatchlings.

In the same group of hatchlings sign of impending molt was first noticed on the morning of August 17, when no. 6 was noted to have its eyes clouded and milky in appearance. By evening no. 1 had attained the same stage and no. 7 was beginning to show it. On the morning of August 20, shedding had begun in no. 6, while no. 2 and no. 8 had milky eyes. The eyes had cleared in no. 1 and no. 7, and were still clear in the remaining hatchlings. On August 22 shedding had been completed by no. 1 and no. 8, and all others were in the process of shedding.

Another clutch of 14 eggs from a recently captured female was found freshly laid in a cage on July 6, 1962. Hatching of 13 occurred August 16 to 20, as shown in Table 11.

Table 11. Times of Hatching in a Clutch of Racer Eggs From Harvey County Park

========+================================+============================= | Time at which shell | Time that hatchling Number | was slit by hatchling | emerged of Egg +---------+----------------------+---------+------------------- | Day | Hour | Day | Hour --------+---------+----------------------+---------+------------------- 1 | Aug. 17 | 10:50 a. m. | Aug. 18 | 3:00 to 6:00 p. m. 2 | Aug. 17 | 12:15 to 12:50 p. m. | Aug. 18 | 3:25 to 4:25 p. m. 3 | Aug. 17 | 1:40 p. m. | Aug. 17 | 10:45 p. m. 4 | Aug. 18 | 3:00 to 6:00 p. m. | Aug. 19 | before 7:00 a. m. 5 | Aug. 16 | 10:45 a. m. | Aug. 17 | 6:30 to 7:55 a. m. 6 | Aug. 17 | 9:00 a. m. | Aug. 18 | 6:30 to 7:30 a. m. 7 | Aug. 17 | 4:15 p. m. | Aug. 20 | 1:00 to 7:00 a. m. 8 | Aug. 17 | 3:40 p. m. | Aug. 18 | 5:00 to 6:00 p. m. 9 | Aug. 17 | 7:30 p. m. | Aug. 18 | 6:30 to 7:30 a. m. 10 | Aug. 16 | 10:48 a. m. | Aug. 17 | 11:05 a. m. 12 | ? | no record | Aug. 18 | 6:00 to 6:30 a. m. 13 | Aug. 17 | 8:00 to 8:20 a. m. | Aug. 17 | 5:30 to 5:50 p. m. --------+---------+----------------------+---------+-------------------

Growth

Hatching usually occurs in late August or early September, and the disparity in size between hatchlings and adults is greater than in some other kinds of snakes. In 76 young from ten clutches of eggs incubated in the laboratory, averages and extremes for measurements and weights were as follows: snout-vent length, 214.5 (186 to 244) millimeters; tail, 59.3 (44 to 73) millimeters; weight, 4.16 (2.4 to 5.8) grams. In each brood the size tended to be fairly uniform, except that there were usually one or more stunted individuals markedly smaller than the others. However, there were striking differences in size between the young of different broods. None of the young captured was as small as the average hatchling from the clutches incubated in captivity, but in the 14 years of my study only four young were captured in August. The hatchlings are relatively secretive and elusive, and the lush vegetation of late summer provides them with abundant hiding places. Nevertheless it is remarkable that the hatchlings are so seldom seem, when their probable abundance is taken into account.

Probably all of those captured had already made some growth after hatching. By early November or the last week of October, racers have almost or quite completed their season of activity, and are at the hilltop ledges, preparing to hibernate, if they have not already retired into dormancy. For 25 young of the year captured in this period at the end of the growing season, measurements and weights were as follows: snout-to-vent, 327 (273 to 418) millimeters; tail 93 (72 to 114) millimeters; weight, 12.3 (7 to 19) grams. In the ten-week period between hatching and hibernation these young had already passed through their period of most rapid growth, having added, on the average, more than 50 per cent to their original lengths, and almost tripled in weight. In these young about to enter their first hibernation, variation in size and weight is much greater than in the hatchlings; some have fared much better than others, and there are significant age differences. Within any one year the time of hatching is spread over several weeks because of differences in the time of laying, and differences in nest sites, with variation in heat received, which promotes or delays the rate of incubation. Year to year differences in the trend of weather increase the dispersion as the incubation time is shortened in hot, dry summers and lengthened in those that are relatively cool and moist.

Table 12. Growth of First-year Racers

=====+=================================+================================= | Original record | Record(s) of recapture +---------------+--------+--------+---------------+--------+-------- | | Snout- | | | Snout- | Sex | | vent | | | vent | | Date | length,| Weight,| Date | length,| Weight, | | milli- | grams | | milli- | grams | | meters | | | meters | -----+---------------+--------+--------+---------------+--------+-------- [M] | Aug. 17, 1959 | 223 | 5.3 | Sept. 12, 1960| 503 | 42 [F] | Oct. 26, 1959 | 278 | 10 | Oct. 26, 1959 | 566 | 55 [F] | Nov. 2, 1959 | 340 | 18 | May 11, 1961 | 582 | 65 [F] | Nov. 10, 1959 | 348 | 13.7 | June 20, 1961 | 733 | 127 [F] | Oct. 19, 1952 | 361 | 15.3 | Oct. 9, 1953 | 620 | 68 [M] | May 9, 1953 | 368 | 17 | May 13, 1954 | 609 | 84 [F] | April 16, 1950| 328 | 142 | Oct. 10, 1950 | 603 | 78.2 [F] | May 17, 1956 | 358 | 15.2 | Oct. 6, 1956 | 575 | 52 [M] | Nov. 1, 1953 | 330 | 11 | May 21, 1955 | 674 | 92 -----+---------------+--------+--------+---------------+--------+--------

Though covering a wide size-range, the young of the year entering hibernation are still a distinct size group, not yet overlapping that of the next older group of young. Growth during the first year of life is best shown by the individuals in Table 12, all of which were marked either before their first hibernation or soon after emerging from it, and were recaptured either the following autumn, or in spring soon after emerging from a second hibernation.

These records indicate that the young racers at the time of their second hibernation have grown to a snout-vent length of well over 500 millimeters, but less than 700 millimeters, and a weight of more than 40 grams but less than 100 grams. Other racers marked in the first few weeks of life were recaptured after two or more seasons of growth, and indicate the sizes that may be expected in young adults from two to five years old, as shown in Table 13.

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 ----+---------------+-----+----+------+--------------+-----+-----+------- [M] | Nov. 12, 1952 | 342 |....| 2-1/2| May 20, 1955 | 702 | 110 | 33 [M] | Nov. 1, 1953 | 330 | 11 | 2 | Aug. 16, 1956| 780 | 162 | 35-1/2 [M] | Nov. 12, 1953 | 293 |....| 2-1/2| May 14, 1956 | 634 | 96 | 32-1/2 | | | | | Oct. 13, 1956| 689 | 110 | 37-1/2 [M] | April 15, 1955| 320 | 13 | 9-1/2| June 8, 1958 | 740 | 118 | 45 [M] | Oct. 2, 1955 | 348 | 18 | 1 | May 22, 1958 | 728 | 120 | 33 | | | | | May 21, 1960 | 795 | 130 | 57 [M] | June 25, 1959 | 378 | 10 | 10 | June 30, 1960| 590 | 60 | 22 | | | | | June 7, 1961 | 705 | 123 | 33 [M] | 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 ----+--------------+-----+-----+-------+---------------+-----+------+------- [M] | Oct. 6, 1960 | 595 | 80 | 13 | July 23, 1961 | 650 | 70 | 23 [M] | Oct. 13, 1950| 525 | 52.6| 13-1/2| Oct. 2, 1951 | 675 | 105 | 25 [M] | Nov. 2, 1950 | 545 | 55.6| 14 | Oct. 24, 1951 | 670 | 100 | 26 [M] | Sept. 2, 1957| 522 | 57 | 12 | Oct. 14, 1958 | 690 | 103 | 25-1/2 [M] | Oct. 17, 1953| 558 | 47 | 13-1/2| May 10, 1955 | 718 | .... | 32 [M] | Nov. 14, 1956| 587 | 57 | 14-1/2| May 20, 1958 | 728 | 100 | 52-1/2 | | | | | June 17, 1959 | 880 | 219 | 64-1/2 [M] | Sept. 7, 1959| 533 | 45 | 12 | June 6, 1961 | 740 | 112 | 33 [M] | Oct. 17, 1959| 558 | 56 | 13-1/2| July 21, 1960 | 625 | 63 | 22-1/2 | | | | | June 7, 1961 | 670 | 95 | 33 [M] | Oct. 16, 1952| 577 | 62.0| 13-1/2| May 31, 1955 | 809 | 160 | 45 | | | | | May 11, 1956 | 855 | 144.3| 56-1/2 [M] | Oct. 11, 1950| 570 | 65.9| 13-1/2| July 11, 1956 | 820 | 193.6| 82-1/2 [M] | Oct. 14, 1953| 560 | 52 | 13-1/2| June 29, 1958 | 794 | 256 | 70 [M] | Oct. 6, 1950 | 563 | 55.8| 13 | Sept. 28, 1958| 907 | 243 | 109 [M] | Oct. 14, 1953| 523 | 44 | 13-1/2| May 19, 1959 | 818 | 190 | 80-1/2 | | | | | May 17, 1960 | 850 | 211 | 92-1/2 [M] | Oct. 13, 1953| 521 | 50.1| 13-1/2| May 13, 1958 | 814 | 166.4| 44-1/2 | | | | | June 3, 1959 | 826 | 165 | 47 [M] | Nov. 5, 1953 | 512 | 34 | 14 | May 22, 1958 | 847 | 135 | 69 [F] | Aug. 11, 1953| 534 | 39.2| 11-1/2| Sept. 18, 1954| 670 | 143 | 24-1/2 [F] | Oct. 14, 1949| 588 | 55.2| 13-1/2| Oct. 11, 1950 | 713 | 114.0| 25-1/2 [F] | Oct. 6, 1950 | 570 | 60.4| 13 | Oct. 11, 1951 | 783 | 174 | 25-1/2 [F] | Oct. 31, 1953| 582 | 58 | 14 | Oct. 5, 1954 | 860 | 195 | 25 [F] | Oct. 21, 1959| 588 | 63 | 13-1/2| May 7, 1961 | 730 | 120 | 32 [F] | May 14, 1960 | 506 | 34 | 20-1/2| Oct. 26, 1960 | 690 | 90 | 26 [M] | Oct. 22, 1960| 527 | 45 | 13-1/2| Oct. 7, 1961 | 620 | 74 | 25 [M] | May 3, 1960 | 530 | 48 | 20 | May 16, 1961 | 700 | 110 | 32-1/2 [M] | 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.

[Illustration: Fig. 18. Graph from records of blue racers marked early in life and recaptured, showing average and extreme snout-vent lengths for males and females of various ages. Growth is especially rapid in the first year, but continues, with gradual slowing, throughout life. In hatchlings, the sexes are of approximately equal size, but females grow to be markedly larger than males.]

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[A] | 190 | 58-1/2 September 12, 1960 | 930 | 249[A] | 238 | 72-1/2 September 14, 1961 | 1012 | 268[A] | 332 | 84-1/2 _No. 8, female_ | | | | June 23, 1955 | 601 | 175 | 67 | 22 August 3, 1958 | 920 | 255 | 300[B] | 60 July 23, 1959 | 955 | 281 | 211 | 71 May 18, 1960 | 962 | 262 | 260 | 81 ---------------------+-------------+-------------+--------+---------- [A] Incomplete. [B] With food.

[Illustration: Fig. 19. Graph from records of blue racers marked early in life and recaptured, showing average and extreme weights in samples of different ages. Early in life the females outstrip males in growth and the size differential increases throughout life.]

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