Influences of a Thermonuclear Cratering Test on Close‐In Populations of Lizards

Following the Sedan test of July 6, 1962, adult Cnemidophorus tigris, Crotaphytus wislizeni, and Uta stansburiana were exterminated to a distance of 4,000 ft from ground zero. Very few adult lizards of any species were observed within 6,000 ft of ground zero during August and November 1962, but the posttest observations in 1962 may have reflected seasonal inactivity. Sampling in June of 1963 indicated that the apparent absence of adults within 4,000 ft was real. No changes attributable to the test were detected at 8,500 to 9,000 ft. Eggs of the three species hatched following the tests in areas where adults did not survive. Young Uta stansburiana were numerous in August from 2,600 to 9,000 ft from ground zero. By October, the young lizards at 2,600 ft were gone, and mortality at 3,800 ft was extremely heavy. At 9,000 ft the apparent density of young Uta was only slightly reduced as compared to that in August. In June of 1963, adults of the three species were observed between 4,500 and 5,000 ft from ground zero, and Uta was apparently most abundant. It is possible that Cnemidophorus is more sensitive than Uta to the deleterious influences involved in this study. The immediate mortality within 4,000 ft is attributed to the gross physical effects of the detonation–dirt fall and blast–which destroyed all of the vegetation out to 2,000 ft and caused partial damage to 5,000 ft from ground zero. Delayed mortality–as that exhibited by juveniles which hatched after the test–is attributed to destruction of habitat. Neither the depletion of food resources nor the residual gamma radiation is likely to have been lethal. Absorbed tissue doses, as registered by three microdosimeters implanted in lizards before the test and recovered July 28 were probably significantly less than the free—air dose registered in the same area.