Phenological Shifts in Loggerhead Sea Turlte Nesting Dates

Abstract

In 2007, the newest report of the Intergovernmental Panel on Climate Change (IPPC) stated that warming of the global climate system is now occurring at an unprecedented rate. Scientists have observed significant temperature changes in both the air and ocean, and predict that there is more warming yet to come. Sea turtles may be sensitive to global warming due to two features of their life history: temperature dependent sex determination (TSD), and high nesting site fidelity. With TSD the temperature of incubation determines the sex of the hatchlings with high temperatures yielding females and low temperatures yielding males. Local temperature shifts in turtle-nesting regions may affect the gender balance of one or several sea turtle species. Sea turtles might prevent sex skewing by nesting earlier in the season. I looked for a temporal response to climate change in loggerhead sea turtles (Caretta caretta) by conducting multi-level regression analysis on first nesting dates from ninety beaches in the Southeast United States over a 30-year period. Loggerhead sea turtles arrived 0.2 days earlier every year over this period, 1.4 days earlier for every point increase in the NAO index, and 3.6 days later for every degree increase in latitude. These results suggest that loggerheads are capable of a behavioral response to climate variability and appear to be responding to long-term trends.