Female reproduction in the western diamond-backed rattlesnake, Crotalus atrox (Serpentes: Viperidae), from Arizona

Reproductive tissue was examined from 46 sexually mature female Crotalus atrox specimens from Arizona, and additional data were obtained from gravid females held in the laboratory and from palpation of live snakes in the field. Mean litter size for 19 females was 8.3 ± 2.6 SD range = 5-15 based on enlarged (> 12 mm) ovarian follicles, but was significantly less in 10 records of oviductal ova or whole litters, at 5.6 ± 1.5 SD, range = 4-9, with an overall mean of 7.3 ± 2.6 for adult females averaging 797 mm SVL, range = 648-1010. These values are lower than estimates in the literature from elsewhere, but seem consistent with the smaller observed size of adult females in the desert region where the samples originated. The number of enlarged follicles correlated positively with female SVL, but oviductal eggs and neonates did not. Four values for RCM ([clutch mass]/[gravid female mass]) averaged 0.303 ± 0.099 SD, range = 0.222 - 0.438. Twenty-one neonates born to wild-caught females averaged 319.7 mm total length and 19.6 g body mass. Enlarged ovarian follicles (> 12 mm length) were found February-June (ovulation during present year) and September-November (ovulation next year), and young are born in late July to September. The earliest field dates for appearance of neonates (n = 75 observed) were 8-11 August. Yolk deposition is normally completed over two activity seasons, although there was some indication that during times of great abundance for rodent prey, individual females might reproduce in successive years. On average, approximately half of all females reproduce in a given year, but significantly higher proportions (73%) were gravid in years of higher compared to lower rodent abundance (28% gravid).