PIVERS ISLAND — Looking at a sea turtle you might not guess that they have excellent hearing. What these turtles are listening for, though, remains a mystery yet to be solved. Tackling this question head on, I was part of a team of researchers from Gettysburg College who traveled from Pennsylvania to the North Carolina coast this past summer to look at how the tiniest turtles, loggerhead hatchlings, use sound in their everyday lives.
While sea turtles lack external ears, they have all the internal parts needed to listen to the many sounds of the world, both natural and those sounds produced by humans. In fact, sea turtles hear low frequency sounds the best. These sounds include noises like crashing waves on the beach, boat motors, cars and human conversation.
Since sea turtles don’t appear to communicate by emitting sound, researchers believe that they must be using their hearing abilities for other purposes, such as listening for an approaching predator or listening to the sound of crashing waves or crawling prey.
For hatchling sea turtles on the beach, the biggest opportunity to utilize their hearing ability is directly after they hatch while orienting toward the ocean during a process known as seafinding. About the size of the palm of your hand, hatchling sea turtles emerge from their nest in the middle of the night and scurry down the beach toward the water to begin their long journey out to sea.
Typically, hatchling sea turtles rely most on visual and slope cues to find their way to the water’s edge, which is why beach lights are prohibited in certain places during nesting and hatching season. Whether or not these hatchlings might also be using acoustic cues, such as listening for the sound of crashing waves, has remained largely unstudied.
Working with the North Carolina Wildlife Resources Commission, Gettysburg College Assistant Professor Wendy Piniak and I set up an orientation arena at the Duke University Marine Lab in Beaufort to test whether acoustic cues might play a role in hatching orientation on the beach.
Using wave sounds recorded directly in front of nests, Piniak and I examined how well sea turtles could orient to the source of the sound. To make sure that these sea turtles weren’t using their other senses to navigate, we performed the experiment in a lightproof tent on a level, circular platform. Watching on infrared cameras from outside the tent, we examined how well the turtles oriented to the source of the sound by recording the turtles crawling direction.
During peak hatching season in August and September, with the help of local volunteers, Piniak and I were able to collect and examine orientation to wave sounds in 200 turtles from beaches all along the North Carolina coast, including Atlantic Beach, Emerald Isle, Carolina Beach and Fort Fisher.
Though its too early to say how well the sea turtles could orient to the sound of crashing waves, Piniak and I are currently analyzing our data and excited to uncover the answer. It is our hope that once we have a better understanding of what types of sounds these turtles are listening for, we can then begin to look at whether anthropogenic sounds, like cars or beachgoers, might be affecting the turtles’ normal orientation behaviors.
Research involving the sea turtles mentioned in this story is authorized under Gettysburg College Institutional Animal Care and Use Committee protocol #2015F1 and North Carolina Wildlife Resource Commission permit #16ST77.
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