Chapter 7 of 13 · 3998 words · ~20 min read

Part 7

May 11 to May 15: 14 June 5 to June 9: 0 May 16 to May 20: 5 June 10 to June 14: 2 May 21 to May 25: 8 June 15 to June 19: 2 May 26 to May 30: 13 June 20 to June 24: 0 May 31 to June 4: 1 June 25 to June 30: 1

Approximately 87 per cent of the records fell in the twenty-day interval, May 11 to 30, which is regarded as the main breeding season. Presumably males continue to be at the peak of breeding condition and continue to search for females after the latter have become unreceptive, partly explaining the scattering of records through most of June.

Several of the females found in traps with males in May had abundant

## active sperm in their cloacae and oviducts and probably had been

inseminated within a few hours of the time they were checked. Others lacked sperm, but the cramped quarters inside the traps may have effectively prevented the consummation of courtship, especially when two males were confined with the same female. None of the females trapped with males in October was found to be inseminated, and it seems doubtful whether copulation ever occurs at that time of year, although males have motile sperm and seem to be in breeding condition then.

_Cycle of the Male_

Cloacal smears indicate that males mature sexually and first produce sperm in August and September when they are a little more than a year old. Insofar as could be determined, there was no sexual activity at this time of year, and actual breeding of the adolescent racers was postponed until the following May. By this time at an average age of 20 months, the snakes had made further growth.

[Illustration: Fig. 16. Catches, in semi-monthly periods, of racers in their summer habitats, at Harvey County Park (upper) and at Reservation and Rockefeller Tract (lower). Intensive activity in spring (the breeding season), tapering off rapidly as the season advances, is well shown by the larger sample, but in the years of trapping at Harvey County Park operations usually were not fully underway until the latter part of May.]

Mr. Dwight R. Platt studied the changes in the male reproductive organs during the annual cycle at Harvey County. In racers recently emerged from hibernation he found the seminiferous tubules filled with Sertoli syncytium, but containing few germ cells. Spermatogonia proliferate in May and June. During the first half of July primary spermatocytes are the dominant cells in the seminiferous tubules. By early August spermatids are dominant and the first free spermatozoa are present. In late October spermiogenesis is essentially complete and the tubules are relatively empty before the snakes hibernate. During the season of activity the seminiferous tubules increase to approximately double their minimum diameter, reaching the maximum in August. Cyclic changes in size and secretory activity of the ductus deferens, ductus epididymis, and sexual segment of the renal tubules occur, with maximum size and secretory activity coinciding with the time of movement and storage of the spermatozoa. The latter are stored in both ductus deferens and ductus epididymis. Despite the short breeding season, a male racer has active sperm at all seasons.

_Eggs_

In accounts of the racer in the humid southeastern United States, Brimley (1903:261), Wright and Bishop (1915:160) and Tinkle (1959:195) mentioned the ease with which the eggs might be found and the superficial situations in which they were sometimes deposited. Both Wright and Bishop, and Tinkle made field studies in swamps, where presumably the subsoil was saturated with moisture and too wet for the eggs. Tinkle mentioned finding one clutch beneath a discarded newspaper and another beneath a small, thin board. Surface (1906:167) stated that in Pennsylvania the eggs were to be found in loose soil, in sawdust piles, or in decaying wood of hollow logs or trees. Clark (1949:249) stated that in northern Louisiana the eggs are laid in soft, moist soil such as may be found beside decaying logs. Minton (1944:457) found two clutches under flat stones on hillsides in Indiana. In the more arid climates of the far western states the species' habits are much different in this regard. Through many years of familiarity with _C. c. mormon_, I have never seen its eggs. Presumably nests in this part of the range are deep underground, most often in old burrows of the pocket gopher (_Thomomys_), which are so abundant that in many areas the soil is riddled with them. Burrows of the ground squirrels (_Spermophilus_ sp.) and other small digging mammals also provide potential insulated nest sites with the favorably moderate temperatures and high humidities that the eggs of snakes require.

On the morning of July 10, 1962, I was directed to the sites of two clutches recently plowed up, 1-1/2 miles north of the Reservation (Pl. 21, Fig. 2). The eggs were in a fallow field having a stand of sunflowers three to five feet high. The plow blades turned the soil at a depth of approximately seven inches. In each instance only a few eggs were visible. They were well scattered in the loose soil turned up by the plow; 21 were found in one clutch and 10 in the other. All the eggs were intact except two that had minute punctures from which liquid oozed. Seemingly the eggs _in situ_ had been well above the level of the blade--at depths of four to five inches. No nest cavities were discernible where the eggs were found, but elsewhere in the field tunnels of moles (_Scalopus aquaticus_) and prairie voles (_Microtus ochrogaster_) were exposed by the plow. Presumably the eggs had been in such tunnels, which had disappeared as the loose soil crumbled. Another clutch was discovered in an adjoining field on July 16. The nine eggs were at depths ranging from 6-1/2 to nine inches, and only the two topmost eggs had been turned up by the plow. All three clutches were within a few feet of the edges of the fields.

On the Reservation and nearby areas I have seen remains of an estimated 20 clutches that have been destroyed by predators. The remains in every instance consisted of an excavation, and the strewn torn and empty eggshells. Nests were at depths of four to eight inches in old tunnels, which most often seemed to be those of moles but also included some of the prairie vole, and perhaps some of the pine vole (_Microtus pinetorum_). All these nests were in open sunny places in prairie or pasture habitat.

Table 7. Numbers and Sizes of Eggs in Clutches of the Blue Racer From Eastern Kansas

========+===============+=================+==============+============== Number | | | | Snout-vent of | Lengths | Widths | Weights | length of Eggs | (mm.) | (mm.) | (grams) | female (mm.) --------+---------------+-----------------+--------------+-------------- 17 | 26.5(29-24) | 17.0(19.0-16.5) | 5.5(6.0-4.4) | 892 8 | 33.3(39-31) | 16.3(17.5-14.0) | 6.0(6.7-5.6) | 899 12 | 29.1(32-25.5) | 17.1(18.5-16.0) | 4.9(5.2-4.4) | 773 14 | 26.9(30-24) | 19.2(20-18) | 5.2(6.2-4.4) | 772 10 | 31.7(33-29) | 16.5(18-15) | 6.0(6.5-5.6) | 807 11 | 29.7(33-27) | 16.7(18-15) | 5.4(5.8-5.0) | 858 21 | 28.9(32-27) | 18.4(19.5-18) | 5.9(6.3-5.6) | 1038 13 | 30.7(34-28) | 19.3(20-18) | 6.8(7.5-6.1) | 907 18 | 29.0(30-26) | 17.9(19-16) | 4.9(5.5-4.3) | 911 12 | 30.3(34-28) | 17.8(19-15) | 5.2(6.1-3.8) | 843 14 | 30.9(36-29) | 19.4(21-18) | 6.8(7.6-6.2) | 846 --------+---------------+-----------------+--------------+--------------

Many observers have described the eggs of the racer, which are white, elliptical, somewhat elongate, with tough, leathery, somewhat flexible, shells, and a granular surface. Like other snake eggs, those of the racer gradually absorb moisture during incubation. They become more turgid and increase in weight and dimensions, especially in breadth, and by the time of hatching are nearly twice their size at laying. Between different clutches and even within the same clutch there is notable variation in the size of the newly laid eggs. Munro (1948:199) noted that in a small adult racer kept by him, the eggs laid were larger but less numerous than those produced by a large adult. Munro noted also that shape of eggs in the two clutches differed; the smaller snake produced more elongate eggs of smaller diameter. The idea that eggs laid by the smaller females are more slender and elongate is not supported by my own data. For 11 clutches of eggs examined soon after laying, dimensions, weights, and the lengths of the females are shown in Table 7.

In a clutch of eggs beginning to hatch on September 3, 1958, dimensions and weights were as follows: length 31.8 (36-30), diameter 22.0 (24-21), weight 9.7 (10.3-9.3).

Gravid females that were kept in captivity in anticipation of their laying usually produced their clutches within a few days. The laying dates of such individuals are shown in the following list. Those with asterisks were from the Harvey County study area, others were from the Reservation and Rockefeller Tract.

June 19, 1961 July 1, 1961 July 12, 1961 June 21, 1959 July 4-5, 1962* July 15, 1961* June 23, 1961* July 6, 1955 July 18, 1961* June 26, 1959 July 7, 1959* July 20, 1961 June 29-30, 1962* July 7, 1959* August 8, 1960*

A further indication of the period when laying occurs was provided by the appearance of females gravid and progressively more swollen with eggs, then their abrupt disappearance and replacement by thin and wrinkled individuals that obviously were recently parturient. The following records show the course of these events on the Reservation in the years when summer trapping was done with sufficient consistency. These dates provide a rough approximation of the time when laying occurs locally. They indicate a laying season concentrated in a period of approximately three weeks in this locality. Records from published literature also indicate that laying occurs in late June and early July at the latitude of Kansas, but somewhat earlier in the southern United States.

Table 8. Dates When Parturient and Gravid Racers were Captured on Reservation and Rockefeller Tract in Several Years, Indicating Time of Oviposition

Many authors have made statements regarding the size of the clutch in the racer, on the basis of those found in the field, those laid after capture, or those dissected from gravid females. Some of the statements were based upon small but unspecified samples, and are far from the mark. From records accumulated in the course of my own field work, and a summarization of those in published accounts a substantial sample is available showing the usual size of clutch in the area of my study, and the trends of geographic variation in some parts of the range.

_C. constrictor_ (all combined) 151 clutches averaged 10.61 (2 to 31) eggs. _C. c. constrictor_ 14 clutches averaged 16.80 (7 to 31) eggs. _C. c. priapus_ 11 clutches averaged 12.60 (7 to 21) eggs. _C. c. mormon_ 43 clutches averaged 5.79 (2 to 13) eggs. _C. c. flaviventris_ 82 clutches averaged 11.78 (5 to 26) eggs. _C. c. stejnegerianus_, one clutch contained 10 eggs.

In the foregoing list the sample of _C. c. flaviventris_ may be divided as follows:

Reservation and vicinity: 36 clutches averaged 11.65 (6 to 21) eggs.

Harvey County study area: 21 clutches averaged 12.0 (5 to 18) eggs.

Museum specimens from Kansas: five clutches averaged 9.2 (6 to 14) eggs.

Published records (Kansas, Indiana, Iowa, Louisiana, Missouri, Oklahoma, Texas): 20 clutches averaged 12.5 (5 to 22) eggs.

Table 9. Published Records Indicating Dates of Laying in Different Populations of Coluber constrictor

Published records of clutches laid by racers, from which figures used in the foregoing account were obtained, include the following:

_C. c. constrictor_: 22 (Barbour, 1950:104); 21, 13 (Brimley, 1903:261); 25 (Conant, 1938:55); 8 (Ditmars, 1907:284); 7, 12, 14, 16, 19, 20, 31 (McCauley, 1945:76); 14 (Wright and Wright, 1957:136).

_C. c. flaviventris_: 7 (Anderson, 1942:210); 22 (Brumwell, 1951:205); 11 (Carpenter, 1958:114); 8, 9, 9 (Force, 1930:31); 10 (Guidry, 1953:50); 18 (Liner, 1949:230); 5, 8, 17 (Marr, 1944:484); 5, 14 (Munro, 1948:199); 13, 19 (Ortenburger, 1928:183); 6, 15 (Tinkle, 1959:195); 15, 19 (Wright and Wright, 1957:141).

_C. c. priapus_: 20, 21 (Cagle, 1942:187); 7 (Conant, 1938:55); 19 (Rossman, 1960:219); 5, 9, 11, 14 (Wright and Bishop, 1915:160); 16 (Wright and Wright, 1957:147).

_C. c. mormon_: 13, 9, 8, 5, 5, 5, 4, 4 (Cunningham, 1959:17); 5, 6 (Stebbins, 1954:374); 6 (Van de Velde, Martan and Risley, 1962:212); 3, 6 (Wright and Wright, 1957:144):

_C. c. stejnegerianus_: 10 (Auffenberg, 1949:54).

In general, the number of eggs in the clutch is proportional to the size of the female producing them. The larger and bulkier females produce more eggs. Geographic trends in number of eggs produced are perhaps controlled by differences in size between different populations; thus, the large eastern _constrictor_ produces nearly three times as many eggs per clutch as does the small western _mormon_, whereas the centrally located _flaviventris_ is somewhat intermediate in size and in numbers of eggs produced.

In most reptiles growth in length and bulk continues after attainment of sexual maturity. For many kinds including _Eumeces fasciatus_, _Crotaphytus collaris_, _Cnemidophorus sexlineatus_, _Agkistrodon contortrix_ (Fitch, 1954:60; 1956:236; 1958:36; 1960:174), and _Sceloporus olivaceus_ (Blair, 1960:94), it has been shown that the larger and older females in a population produce more offspring than do the smaller and younger individuals. This situation applies in the racer, as shown by the clutches of 52 females correlated with their sizes and presumed ages (Fig. 17, Table 10). The two-year-olds contribute a relatively small quota to the annual brood, partly because their clutches are small, but more especially because many of them fail to attain sexual maturity in time to breed. Many of the female racers that are more than two years old also fail to produce an annual clutch of eggs. The 24-day period May 28 to June 20 inclusive is judged to comprise the period when eggs have generally enlarged sufficiently to be detected in gravid females, but still have not been laid in most instances. In this period, in 1960, 1961 and 1962, ratios of gravid females to those not detectably gravid in several supposed age groups arbitrarily established on the basis of size, were as follows:

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

[Illustration: Fig. 17. Graph showing number of eggs per clutch, and correlation with supposed age (as deduced from length of body) in female blue racers from the Reservation, Rockefeller Tract, and Harvey County Park.]

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.