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Phenological shifts, by initiating reproductive events earlier, in response to advanced seasonal warming is one of the most striking effects currently observed in wild populations. For sea turtles, phenological adjustment to warming conditions could be the most effective short-term adaptation option against climate change. We calculated future phenological changes required in seven important loggerhead (Caretta caretta) nesting populations to continue achieving a high hatching success and a sex ratio that lies within current ranges. Considering temperaturemediated phenological changes, we found that most populations (six out of seven) will not be able to keep pace with a warming climate. Under an optimistic climate warming scenario (RCP4.5), these populations will face a climatic debt, that is, a difference between required and expected phenological changes, and warming will substantially reduce hatching success and induce a feminization of hatchlings, which may jeopardize their reproductive sustainability. Our approach offers the possibility to quantify the efficiency of phenological shifts in oviparous reptiles by considering physiological, developmental and phenological processes.

The conservation of large, long-lived turtle species can be a challenging issue because their life-history strategies make populations sensitive to changes in adult survivorship and populations may be difficult to sample. The Alligator Snapping Turtle (Macrochelys temminckii) is a large freshwater turtle species occurring in North America for which commercial harvest has severely reduced populations throughout the species range. Given recent population declines and a general deficit of demographic knowledge for Macrochelys, we conducted a mark-recapture study of M. temminckii from 1997-2013 in Spring Creek, Georgia, USA. We made 166 captures of 75 individuals using baited hoop-net traps and skindiving searches. The observed and estimated population structure described the adult sex ratio as even and adults as more abundant than juveniles. Apparent survival was higher for adult males (0.98) and females (0.95) than for juveniles (0.86), and we estimated a population density of 13-14 turtles/stream kilometer. The survival estimates for adult M. temminckii are among the highest of all freshwater turtle species reported in the literature. We used the empirical demographic parameters described here and a literature review to build an updated population model for M. temminckii; the model estimated a finite rate of population increase consistent with a growing population (k ¼ 1.036) at Spring Creek, and population viability analysis found the population growing over the next 50 yr in 100% of simulations. Application of our model to published survival estimates from two impacted western populations indicated a declining population (k ¼ 0.563) with a high risk of extirpation in Oklahoma and a population with a slow rate of decline (k ¼ 0.978) but approaching stability in Arkansas. Simulations identified combinations of survival values which generate viable populations and also characterized population structure resulting from viable scenarios. This is the first study to document a stable and viable population of Macrochelys. We suggest that the population parameters described at Spring Creek are the best approximation of reference demographic conditions for Macrochelys to date, and this study provides a general framework applicable for large, long-lived, endangered turtle species for which demographic data are unavailable.

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