Large-scale investment in the excavation and “camouflaging” phases by nesting Leatherback Turtles (Dermochelys coriacea)

Abstract

Nesting female Leatherback Turtles (Dermochelys coriacea (Vandelli, 1761)) are ungainly and vulnerable to predation, stranding, and physiological stress, dangers encountered repeatedly in a nesting season. Minimising these risks must be balanced against optimising investment in nest-site selection, excavation, refilling, and concealment of their egg clutches. We investigated the relative investment in the different phases of nesting in Leatherback Turtles by recording the duration of, and respiratory frequency during, each phase. Nest excavation and the final sand scattering (usually termed “camouflage” or “disguise”) phases were the longest in duration. By combining the relative durations of nesting phases with literature estimates of oxygen consumption, we found that these may be the most expensive phases energetically, sand scattering in particular. Leatherback Turtles follow convoluted paths during the sand scattering phase, which were mapped and measured. They disturb large areas (mean (±SD) 30.3 ± 11.1 m2, maximum 57 m2), the centroids of which were always offset from the nest itself. Interestingly, in none of 26 nestings observed did the centre line of females move over the nest itself. Nesting Leatherbacks therefore invest heavily in obscuring the egg clutch, and the pattern of their movements in doing so suggests decoy behaviour.