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Part 9

Natural History of the Racer Coluber Constrictor · Henry S. Fitch — chapter 9 of 27 · ~1,842 words · public domain

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:

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