ical pathology parameters did not meet the criteria for partitioning by season for the purpose of calculating separate reference intervals. However, several analytes did exhibit statistically significant differences by season. Juvenile loggerheads sampled during the fall for this study had higher estimated white blood cell and heterophil counts relative to turtles sampled during the summer. In addition, there was a negative correlation between water temperature and the estimated white blood cell and heterophil counts. Increased numbers of granulocytes can indicate a stress leukogram in reptiles \[[@pone.0115739.ref035],[@pone.0115739.ref036]\], and could reflect a stress response by the loggerheads to decreasing photoperiod and cooler temperatures in the fall.

As water temperatures cool during the fall months, there is an influx of loggerhead sea turtles from northern areas into NC waters, as they migrate southward along the coast to warmer areas \[[@pone.0115739.ref012],[@pone.0115739.ref014]\]. Throughout migration, sea turtles are exposed to many physiologic stressors including changes in temperature, salinity, and food availability \[[@pone.0115739.ref020]\]. There was not a mechanism to discern between resident and migrant loggerhead turtles in this study; therefore, variation in clinical pathology parameters by migratory status could not be assessed directly. The higher estimated white blood cell and heterophil counts in turtles sampled during the fall months may be partly explained by migrants within the sample of loggerheads in the fall. A previous survey of juvenile loggerhead sea turtles in Core and Pamlico Sounds in North Carolina reported a relatively higher percentage of heterophils in migratory turtles compared to residents \[[@pone.0115739.ref020]\]. The migrants also had lower lymphocyte and eosinophil counts providing further evidence of a stress leukogram in this group of turtles \[[@pone.0115739.ref020]\]. There was no seasonal variation in lymphocyte or eosinophil counts in the current study.