Every summer, turtle hatchlings have to quickly dig up the sand of their nests and start a perilous journey towards the sea. This delicate process is very energy consuming, but there’s power in numbers. A study found baby turtles will help each other dig the sand, and this social facilitation results in net energy savings for the group. In some cases, this behaviour helps the baby turtles hatch five days earlier than they would in smaller groups and provides a seven-fold energy saving.
Across beaches all over the world, baby turtles start hatching around mid-June to August. The exact time a nest is ready to hatch is difficult to predict. Like all babies, the hatchlings decide when they are ready.
When a sea turtle nests, she digs a hole deep in the sand, lays her eggs in the hole, then covers the eggs with sand to hide them from predators. After nesting she returns to the sea, leaving tracks as she crawls across the beach. She never comes back to check on the eggs or hatchlings, but researchers often use these tracks left by females to identify nests.
Six to eight weeks later, depending on the temperature of the sand, the baby turtles are ready to hatch. But unlike baby alligators, which are liberated from their nest by the mother, sea turtle babies must hatch and fend all by themselves — there are no adults around.
First, to break the shell, the hatchlings use their “caruncle”. This temporary egg-tooth is an extension of the upper jaw that falls off soon after birth. When they decide to hatch, typically at night or during a rainstorm when the temperature is cooler, they do so in massive groups.
Once outside, the turtles burst out towards the brightest horizon and dash toward the sea as a group. They have to move quickly if they want to survive. Many will die of dehydration in the sun and eaten by the birds and crabs. Once in the water, the hatchlings are carried by currents and seaweed to the open ocean where other dangers await: sharks, big fish and circling birds. Only one in a thousand babies survives to adulthood.
Mohd Uzair Rusli, a biologist at the University of Malaysia Terengganu in Kuala Terengganu, has known for a long time that social facilitation is key to the group hatching of sea turtles. The reasons for this massive collaboration were unclear, though.
His hunch was that it was all about saving energy, so he and colleagues buried hot zones of 10 to 60 eggs in the sand, and measured how much oxygen each hatchling used. This simple, but effective experiment revealed that those babies hatched in larger groups got out of the sand in three days, rather than eight, and used just over one-seventh the energy employed by hatchlings from smaller groups.
The findings could prove extremely important for conservation efforts. Sometimes, conversation workers collect turtle eggs from the beach and move them to hatcheries where they’re positioned in small batches.
“Reducing the number of eggs in a clutch may ultimately result in the production of hatchlings with reduced energy reserves when they enter the sea,” Rusli says.
Next, Rusli and team plan on unvailing the social dynamics involved in the beach exodus. “It would be interesting to discover if the labour of digging is shared equally amongst clutch mates, or if there are a few individuals that are up front almost continuously and do the majority of digging work,” he says.