Part 10

Two-year-olds 2 gravid, 13 apparently not gravid Three-year-olds 5 gravid, 4 apparently not gravid Four-year-olds 3 gravid, 2 apparently not gravid Five-year-olds 4 gravid, 3 apparently not gravid Six-year-olds (or older) 8 gravid, 2 apparently not gravid

From the appearance of these snakes it is reasonably certain that none had already laid eggs when it was recorded, but there is some possibility that a few individuals not noticeably gravid at the times they were examined, produced eggs subsequently. However, these meager data do seem to indicate that most of the two-year-old females and a minority of older individuals fail to produce clutches in the annual breeding season.

Table 10. Fecundity of Female Racers in Various Age-size Classes, All From the Reservation and Rockefeller Tract

========================+===========+=====================+============== Most Probable Age | Number of | Snout-vent length | Number in Years of Females | females | of females; average | of eggs in (as indicated by size) | in sample | and extremes | clutch ------------------------+-----------+---------------------+-------------- 2 | 10 | 688 (589-748) | 9.2 (6-12) 3 | 19 | 789 (756-840) | 9.9 (5-14) 4 | 7 | 856 (850-861) | 10.8 (8-12) 5 | 6 | 907 (892-933) | 13.0 (8-17) 6 or more | 10 | 1005 (955-1088) | 15.7 (11-19) ------------------------+-----------+---------------------+--------------

Under unfavorable conditions eggs can be resorbed, but probably this can occur only if initiated before ovulation. A racer in which six small eggs were palped on June 28, 1960, was kept until July 23 but did not oviposit. It no longer appeared gravid and the ova could not be detected by palpation. Another female had 13 eggs on June 21, 1960, but by July 23 when the snake was released the eggs had not been laid and no longer could be detected. Both snakes refused to feed throughout their confinement.

Like other reptilian eggs, those of the racer are dependent upon the warmth of their surroundings for incubation. They are tolerant of a wide range of environmental temperatures, but the higher the temperature the more rapidly incubation proceeds. Under natural conditions there may be much difference in hatching time in two clutches laid at the same time and in the same locality. Site of the nest--deep and well insulated, or shallow; in a well shaded situation or one exposed to maximum amounts of sunshine--would largely control rates of development. Clark (1949:249) writing of the subspecies anthicus in north-central Louisiana, stated: "eggs are laid about the first of June.... young begin to make their appearance at about ... July 1." Even for the southern states these dates of laying and hatching seem somewhat too early to reconcile with the records published by other observers, and are in need of verification, especially since they seem to be based upon vaguely remembered observations rather than upon written records. At the other extreme Surface (1906:167) wrote of constrictor in Pennsylvania that hatching may occur as late as October, and that there is evidence some young may even remain in the egg over winter before hatching occurs. Several incubation periods are on record for clutches laid and hatched in captivity, as follows:

C. c. mormon, Oregon, 47 and 51 days (laid July 3, 1961, hatched August 19 and 23; Van de Velde, Martan and Risley, 1962:212).

C. c. stejnegerianus, Texas, 73 days (laid June 5, 1947, hatched August 17, Auffenberg, 1949:54).

C. c. priapus, S. Illinois, 58 and 59 days (laid July 10, 1940, hatched September 6 and 7, Cagle, 1942:187).

C. c. flaviventris, Kansas, 50 days (laid July 4 and 5, hatched August 23 and 24; Munro, 1950:124).

C. c. flaviventris, Texas, 43 days (laid June 9, 1952, hatched July 22; Guidry, 1953:50).

No incubation periods for eggs in natural nests have been recorded. In the course of my study, eggs obtained from 12 captive females were hatched in confinement, with an average incubation period of 51 days (43 to 63) as follows:

Laid July 6, 1955, hatched August 20. Laid July 3, 1958, hatched September 3 and 4. Laid June 21, 1959, hatched August 17. Laid June 26, 1959, hatched August 17. Laid July 7, 1959, hatched August 23 to 25.* Laid June 23, 1960, hatched August 20.* Laid June 30, 1961, hatched August 30. Laid July 15, 1961, hatched September 1 and 2.* Laid July 18, 1961, hatched September 2 and 3.* Laid July 4 and 5, 1962, hatched August 15 and 16.* Laid June 29 and 30, 1962, hatched August 14 and 15.* Laid July 6, 1962, hatched August 16 to 20.*

In the foregoing list those entries marked with asterisks were obtained from the Harvey County study area; all others were from the Reservation and Rockefeller Tract.

Hatching

Detailed observations on hatching were made on a clutch of eggs laid on June 29 and 30, 1962, by a female caught in Harvey County. The first egg in the clutch had already been laid in the trap when the female was found at 11:30 a. m., June 29. Two of the eggs were abnormal, with thin transparent shells, and were found to lack embryos when they were opened on July 7. Later, two other eggs were attacked by mold and the embryos died early in development. The clutch was kept in a can of slightly damp soil. At 2:30 p. m. on August 13, when the clutch was examined, egg no. 6 was found to have hatched. The young snake had made a 21-millimeter slit in the shell. At 12:50 a. m. on August 14, it was discovered that eggs 1, 4, 5 and 7 each had been slit. No. 4 had two parallel slits separated by a two-millimeter strip of shell, and the young racer could be seen inside. At 1:05 a. m. this young snake had changed position and was lying upside down in the egg, his snout protruding slightly through one of the slits. At 1:45 a. m. he was again right side up, still in the shell. At this time each of the slit eggs showed the protruding snout of a young snake. Occasionally the viscous liquid egg white would be blown into a large bubble on the surface of the shell as the young snake exhaled. A third slit, parallel to the others, had appeared in egg no. 4. A hatchling emerged from egg no. 1 between 2:20 and 3:20 a. m., and another from no. 7 between 7:00 and 9:00 a. m. The hatchling struck vigorously many times, and vibrated his tail when he was disturbed. Egg no. 3 was first slit between 7:00 and 9:00 a. m., and three more slits appeared in it between 9:15 and 10:15 a. m. At 12:45 p. m. a hatchling was found in the act of emerging from egg no. 4, and approximately the anterior one-fourth of its body protruded. Disturbed by the movements of the observer, the little snake drew back into its shell. This hatchling began to emerge again at 12:50 and his hatching was completed at 1:00 p. m. Between 5:40 and 6:20 p. m. a hatchling emerged from egg no. 3 (for several hours this hatchling had been lying on its back inside the egg, with only its snout protruding); two slits appeared in egg no. 2 and three slits appeared in egg no. 8. At 6:50 p. m. the hatchling in the latter thrust his snout through the slit in this eggshell. This hatchling was lying on its back at first but by 10:50 it had shifted to a normal position. It emerged from the shell between 2:35 and 2:50 a. m. Egg no. 2 was the last to hatch. At 7:05 p. m. the hatchling inside made two additional small slits in the shell, and at 7:30 p. m. thrust its snout through one of them, while lying on its back. At 1:45 a. m. it was right side up, but at 3:00 a. m. had reverted to its previous position. At 4:40 a. m. it was again right side up, and it emerged from the shell at 5:55 p. m.

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 | -----+---------------+--------+--------+---------------+--------+-------- | Aug. 17, 1959 | 223 | 5.3 | Sept. 12, 1960| 503 | 42 | Oct. 26, 1959 | 278 | 10 | Oct. 26, 1959 | 566 | 55 | Nov. 2, 1959 | 340 | 18 | May 11, 1961 | 582 | 65 | Nov. 10, 1959 | 348 | 13.7 | June 20, 1961 | 733 | 127 | Oct. 19, 1952 | 361 | 15.3 | Oct. 9, 1953 | 620 | 68 | May 9, 1953 | 368 | 17 | May 13, 1954 | 609 | 84 | April 16, 1950| 328 | 142 | Oct. 10, 1950 | 603 | 78.2 | May 17, 1956 | 358 | 15.2 | Oct. 6, 1956 | 575 | 52 | 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.