Variation in Annual Clutch Phenology of Sonoran Desert Tortoises (Gopherus morafkai) in Central Arizona

The phenology of egg production and oviposition in organisms affects survival and development of neonates and thus, both offspring and maternal fitness. In addition, in organisms with environmental sex determination, clutch phenology can affect hatchling sex ratios with attendant effects on population demography. The rapid rate of contemporary climate change might disrupt reproductive phenologies that evolved to match environmental conditions. To better understand the response of clutch phenology to annual and long-term changes in climate, we studied a population of Sonoran Desert Tortoises (Gopherus morafkai) in Arizona in 1993 and 1997–2005, specifically quantifying three phenophases, including (1) the estimated time of appearance of shelled eggs in females, (2) the estimated time that eggs were last visible in X-radiographs, and (3) the duration of the interval between the first two events. The mean date for appearance of shelled eggs was 6 June, and the mean date they were last visible was 26...