Thresholds of visible light detection in hawksbill turtle (Eretmochelys imbricata) hatchlings

Light is the primary environmental cue that hatchling sea turtles use to find the ocean post-emergence from the nest. The process of seafinding is interrupted by any form of light stronger than natural, ambient light. Three of the seven species of sea turtles have been investigated to determine their thresholds of detection for various wavelengths of light across the visible spectrum to help reduce hatchling misorientation. Hawksbill turtles, however, have not yet been investigated, and their general preference for nesting under vegetation, rather than on open sand, justifies the hypothesis that their vision may be more sensitive to lower light intensities than other species. Using a Y-maze choice experiment, we discerned the detection threshold for hawksbill hatchlings for visible light of 415, 470, 535, 555, 590, 601, and 660 nm. Hawksbills were most sensitive to light of 555 nm, least sensitive to light of 660 nm, and exhibited detection thresholds that are intermediate compared to previously studied species of sea turtles. Our results may be critical for informing changes in beachfront lighting, as we illustrate that even at very low intensities, light across the visible spectrum may still attract and misorient hawksbill hatchlings.