Sea turtles employ diversionary tactics to protect nests

Issued: Wed, 27 May 2020 14:35:00 BST

A low angled shot of a sea turtle on a tropical beach

Two endangered species of sea turtles do not disguise their nests and instead create a decoy trail, according to research led by the School of Life Sciences' Professor Malcolm Kennedy.

The paper, published in the journal Royal Society Open Science, deals with how leatherback and hawksbills turtles invest considerable energy protecting their eggs before the females return to the sea.

When these turtles cover the chambers in which they have laid their eggs, they spend significant time and effort on scattering sand around the next site.

Extending their time on the beach in this way exposes them to risks such as predation and exhaustion, and it had been presumed that this activity was a means of camouflaging the nest site from predators.

Its probable true function had not been identified – until now, with these findings strongly supporting the idea that they create a series of decoy nests to reduce discovery of their eggs by predators.

The research, conducted the work over a period of seven years during University of Glasgow Exploration Society expeditions to Trinidad and Tobago, was organised by Professor Kennedy and Tom Burns, the first author, who together realised that conventional ideas about the last phase of sea turtle nesting needed radical correction.

Professor Kennedy, Professor of Natural History, said: "We closely followed the activity and movements of hawksbill and leatherback turtles during the final ‘sand scattering’ phase of nesting and our research shed new light on their nesting behaviour.

"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.

"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.

"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.”

Leatherbacks appear to be nesting better this year because the pandemic lockdown has left beaches in peace, which emphasises the care with which turtles must find safe places to deposit eggs.

Burns TJ, Thomson RR, McLaren RA, Rawlinson J, McMillan E, Davidson H, Kennedy MW. (2020) Buried treasure—marine turtles do not ‘disguise’ or ‘camouflage’ their nests but avoid them and create a decoy trail. R. Soc. Open Sci. 7: 200327.

Image: Jack Rawlinson