The calculated number of eggs pertains to a stage before oviposition, and subsequent losses through resorption under unfavorable conditions, through inviability of embryos and through deaths of some of the gravid females, are to be expected. In the weeks of incubation further losses are sustained. Although these losses cannot be measured, they must be severe as on numerous occasions scattered and torn eggshells representing entire clutches dug out and destroyed by predators, have been found. Probably other clutches are destroyed underground by such predators as moles and egg-eating snakes, and still others by insects. Tinkle (1959:195) wrote that in a clutch of 15 eggs found under a board, four were parasitized and had small perforations. Molds destroy a high percentage of all reptilian eggs that are incubated artificially and doubtless destroy many under natural conditions also. Excessive heat or moisture, or desiccation, resulting either from climatic extremes or from poor choice of a nest site by the female, would cause further loss. In four different years, Blair (1960:108) found that losses of eggs between laying and hatching in the Texas spiny lizard (_Sceloporus olivaceus_) ranged from 69 per cent to 86 per cent; no other comparable study of the extent of egg losses in a species of reptile is known to me. The racer is somewhat less prolific than the spiny lizard, and potentially longer lived; the racer's eggs are larger and thicker-shelled, and they are deposited in deeper burrows. It might be expected that losses during incubation would be somewhat less in the racer than in the spiny lizard. Table 20. Calculated Productivity in a Hypothetical Group of 100 Subadult and Adult Blue Racers ===========+==============+============+============+============+========= | Percentage | Percentage | Percentage | Eggs | Age-Group | of | of fecund | productive | per | Number (years) | population | females in | females in | productive | of eggs | in age-group | age-group | age-group | female | produced -----------+--------------+------------+------------+------------+--------- 2 | 41.5 | 51.2 | 13 | 9.2 | 26 3 | 17.8 | 51.2 | 56 | 9.9 | 51 4 | 12.6 | 51.2 | 60 | 10.8 | 42 5 | 9.5 | 55.0 | 57 | 13.0 | 39 6 and over | 18.6 | 61.3 | 80 | 15.7 | 143 -----------+--------------+------------+------------+------------+--------- Table 21. Percentages of Racers in Each Annual Age Group (Exclusive of Hatchlings) in Autumnal Samples at Different Stages of the Field Study, Showing Shift Toward Older Age-Groups in the Later Years