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.