We examined loggerhead nest temperatures and hatchling sex ratios in an effort to more accurately predict hatchling sex ratios produced from 2 barrier islands in the northern management unit (Blackbeard Island National Wildlife Refuge and Wassaw National Wildlife Refuge, Georgia, United States) from 2000 to 2004. Temperature data loggers were placed into 169 nests to monitor incubation temperatures. Average critical period temperatures ranged from 26.3°C to 33.2°C (mean ± SE, 29.2° ± 0.1°C) and indicated seasonal variation in sex ratios. The sex of 669 hatchlings found dead in nests was histologically evaluated (n  =  212 nests; 14–90 nests/yr). The sex ratios varied from 0% to 100% female per nest (n  =  1–53 hatchlings/nest) and average sex ratio for all nests ranged from 55.5% female in 2003 to 85.4% female in 2002. In addition to monitoring nest temperature, 10 hatchlings per nest were euthanized to verify sex during 2003 on Blackbeard Island National Wildlife Refuge (n  =  10 nests) and 2004 on Wassaw National Wildlife Refuge (n  =  9 nests). Sex ratios were analyzed by using an advanced statistical program for evaluating temperature-dependent sex determination and indicated a 1∶1 temperature (temperature that produces a 1∶1 sex ratio) of 28.9°C. We offer an equation for predicting northern management unit hatchling loggerhead sex ratios by using critical period temperature and tested its validity. Sixteen of 18 nests (n  =  10 hatchlings/nest) showed no significant difference between the predicted sex ratios based on the equation vs. sex ratios obtained through histology. Our data indicated that rookery beaches north of Florida are important areas for the production and recruitments of male loggerhead hatchlings into the overall western North Atlantic Ocean and nests deposited earliest within a nesting season are primary contributors of male turtles. We suggest that nest monitoring programs grant such nests particular protection to increase their survivability and the production of hatchlings.

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