The records obtained from trapping racers in late spring and summer in fields provided a somewhat different picture of the population from the sample obtained along the ledges in autumn. In the former sample there were 400 males to 257 females, but in the latter sample there were 355 males to 379 females. I regard the summer sex ratio as a distorted one, brought about by the greater activity of the males in the breeding season. Racers are caught most easily in May, and the fact that two or more males often were trapped with the same female, while the reciprocal combinations did not occur, demonstrates the increased activity of the males in their search for mates at this season. In autumn there is no sexual activity; both sexes probably are equally active in seeking places to hibernate when they are trapped along the hilltop outcrops. The ratio of 51.6 per cent females in my sample of 734 may indicate that in the males greater activity at other seasons results in a somewhat higher mortality. This idea is borne out by the fact that for the supposed two-, three- and four-year-olds combined, females comprise 51.2 per cent, but they comprise 55.6 per cent of those more than four years old and 61.3 per cent of those more than five years old. [Illustration: Fig. 20. Histograms comparing snout-vent length in random samples of _Coluber c. flaviventris_ (those captured on the Reservation and Rockefeller Tract in 1960 and 1961) and _C. c. mormon_ (specimens in the Museum of Vertebrate Zoology, University of California). In the museum sample, collected by conventional methods, the first-year young constitute a prominent and fairly distinct size group, whereas in the sample of racers from the Reservation and Rockefeller Tract, mostly caught in wire traps of quarter-inch mesh, relatively few young were secured. It is demonstrated that hatchlings are approximately the same length in both populations, but _flaviventris_ grows much longer, and that the differences in length between the sexes is approximately the same in each population.] By assigning to each racer caught an arbitrary age, on the basis of size according to Table 17, I calculated the population (exclusive of those snakes in their first year of life) to have the composition shown in Table 19. Table 19. Percentages of Adult Population of Blue Racers Comprised by Each Annual Age Group =================+=============== | Percentage of Years of Age | population -----------------+--------------- 2 | 41.5 3 | 17.8 4 | 12.6 5 | 9.5 6 | 6.1 7 | 4.3 8 | 2.7 9 | 2.4 10 | 1.2 11 or more | 1.9 -----------------+---------------