2023-10-13 03:04:00
Baby sea turtles, including leatherback turtles (Dermochelys coriacea), usually hatch at night. Young leatherback turtles use the difference in light reflected from the sea to orient themselves. It is because of this method of navigation that turtles that hatch near populated areas often crawl toward the light of buildings and away from the ocean.
When trying to find the ocean, baby leatherbacks sometimes crawl in circles. This “circling” behavior depletes energy and puts the young turtle at greater risk of being captured by a predator such as a crab or seagull.
To understand why leatherback turtles circle, researchers at Florida Atlantic University first studied babies’ sensitivity to light. Scientists have determined that, compared to hard-shelled loggerhead turtles, leatherback turtles are 10 to 100 times less sensitive to light.
The research, published in the journal Animal behavior, revealed that leatherback turtle circles increased when there was a new moon and the night sky was darkest. On the other hand, loggerheads rarely circled, even when they had little light to guide them. The results are surprising because while leatherback turtles feed day and night, loggerhead turtles are known to be active only during daylight hours.
“Leatherback turtles’ eyes are less sensitive to all wavelengths of light than loggerhead turtles, and during a dark night they have difficulty determining the location of the horizon out to sea,” Samantha said. Trail, first author of the study.
“Even so, leatherback turtle hatchlings eventually crawl toward the sea, even during the new moon. It just takes them longer because they stop every so often to circle, which we think allows them to reassess, and possibly confirm, the correct crawling direction.
The real question is why leatherback turtles would remain less sensitive to light when it is so important for their survival. From an evolutionary perspective, this represents a major cost.
Scientists hypothesize that leatherback turtles have not evolved greater sensitivity to light because their difference in vision has other advantages. Perhaps their less light-sensitive eyes allow them to better find prey, mates or suitable habitat – which is possible because loggerheads live in different parts of the ocean.
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Par Zach Fitzner, Threatened-species.fr Editor
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