Two endangered species of sea turtle create “decoy nests” to protect their eggs from predators, new research suggests.
When female sea turtles cover the nest chambers in which they have laid their eggs, they spend considerable time and effort on scattering sand around the site.
Researchers investigated why leatherbacks and hawksbills do this despite the fact that extending their time on the beach in this way exposes them to risks such as predators and exhaustion.
Previously it was thought that this activity was a means of camouflaging the nest site from egg predators.
However, the research, led by the University of Glasgow, now suggests that the turtles create decoy nests away from the main nest site to reduce the risk that predators will discover their eggs.
Professor Malcolm Kennedy, Professor of Natural History at the University of Glasgow, said: “Our research sheds new light on the behaviour of nesting marine turtles. We closely followed the activity and movements of hawksbill and leatherback turtles during the final ‘sand scattering’ phase of nesting.
“Our findings strongly support the idea that they create a series of decoy nests away from the nest itself to reduce discovery of their eggs by predators.
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“This may explain why, despite all the extra risks, female turtles stay on the beach away from the safety of the sea, working to enhance the safety of their eggs,” said Professor Kennedy.
“They can spend longer doing this than for any other part of the elaborate nesting process. Remarkably, we found similar behaviours in two species of turtle that shared a common ancestor over 100 million years ago, while dinosaurs still ruled the land.
“What they do must be extremely important to their offspring, which they will leave behind as eggs in the sand and never see.”
The research was organised by Professor Kennedy and Tom Burns and stretched periodically over seven years.
They joined University of Glasgow Exploration Society expeditions to Trinidad and Tobago, and the study involved work by them and undergraduate students late into the night on remote nesting beaches.
The research paper is published in the Royal Society Open Science journal.
Reader Q&A: Why do sea turtles cry when they lay eggs?
Asked by: Vicky Bateman, St Albans
Reptiles have less efficient kidneys than mammals and they can’t produce urine with a higher salt concentration than the seawater they drink. To avoid poisoning themselves with salt buildup, sea turtles have a gland in each eye that actively pumps salt ions into their tears. They need to run these glands continuously to maintain the correct balance of salt in their bodies.
We associate crying with egg laying because that’s the only time they come ashore, but they cry in the sea as well. The tears also help flush sand from their eyes.