Lunar phases and hawksbill sea turtle nesting

The behavior of sea turtle species can be influenced by the lunar cycle, possibly due to moonlight variability. We analyzed the relationship between nesting behavior and moon phase using nesting hawksbill turtle records for beaches in Northeast Brazil for the 2006–2007 to 2015–2016 seasons. The total number of records was 4807, while the total number with time point registration was 1031. The Eretmochelys imbricata inter-nesting period was approximately half the lunar cycle; we therefore expected nesting phase synchronization with lunar phases within each season. We computed the lunar angle for the hawksbill records, and the Kuiper test for uniformity indicated that the species shows some lunar phase preferences. We observed that oviposition at the first and last quarters of the moon is more frequent than at full moon or new moon phases. We also computed the lunar angle throughout several seasons for remigrant turtles and found an absence of preferential lunar phase across different seasons. This indicates that the hawksbill does not choose a lunar phase previously chosen in other nesting seasons. We analyzed the relationship between the presence of the moon in the sky and nesting turtles, and, in sequence, compared the records of false crawls and nest crawls; no relation was found between these variables.