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, re-filling, 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 30.3 + 11.1 m 2 , maximum 57 m 2 ), 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.

Buried treasure—marine turtles do not ‘disguise’ or ‘camouflage’ their nests but avoid them and create a decoy trail

“…The sand-scattering phase of nesting by hawksbill turtles is, therefore, similar in duration and inferred metabolic effort to the other phases of nesting that involve movement and physical effort, namely excavation and refilling of the egg chamber, as is also the case for leatherback turtles [24].…”

“…However, there are also some notable differences between them. Temporal investment in sand-scattering behaviour, relative to excavation and oviposition, was greater by leatherbacks [24] than hawksbills (figure 1a). Furthermore, leatherback paths while sand-scattering were more circuitous than taken by hawksbills, and there tended to be greater distances between their sand-scattering stations (figure 3e and f; electronic supplementary material, figures S1 and S3).…”

“…We discriminated nesting phases following the descriptors given by Johnson et al [17] and Burns et al [24]. Hawksbills are prone to abandoning nesting if they detect disturbance nearby, so we recorded royalsocietypublishing.org/journal/rsos R. Soc.…”

“…Other authors instead consider that its primary function is to establish beach conditions above and adjacent to the egg chamber for optimal incubation conditions [1,19]. Others still hint at a decoy function [20], but few studies have quantitatively examined sea turtle nesting behaviour (aside from nest site location and nesting frequency) in detail [21][22][23] and fewer still have focused on sand-scattering behaviour [24]. As such, these hypotheses remain essentially unexplored.…”

Impacts of a geotextile container dune core on marine turtle nesting in Juno Beach, Florida, United States

“…false crawl) than those on beaches without an anthropogenic barrier (Mosier ), lowering overall nesting success (the ratio of nests to false crawls). Marine turtles expend tremendous amounts of energy to crawl out of the water onto the beach to nest (Mosier ; Burns et al ). Wasting these energy reserves on unsuccessful nesting attempts could ultimately reduce the number of clutches laid or the number of eggs per clutch, diminishing overall reproductive output (Broderick et al ; Katselidis et al ).…”