Sneaky turtles may create ‘decoy nests’ to throw off predators

New research focusing on post-nesting behaviour has shown that hawksbill and leatherback turtles randomly scatter sand surrounding their nests, to give the impression there are multiple nests grouped together, possibly in an attempt to confuse and deter egg predators.

leatherback returning to sea
A leatherback turtle returns to the ocean after laying her eggs in a nest, but new research suggest she may have also created some decoys as well

Turtle nesting is a key area of research in marine biology that is crucial to understanding turtle reproduction and helping to protect these magnificent ocean reptiles. As a result lots of studies are carried out to look at the numbers of nests, egg laying behaviour, nest selection, temperature sex determination, the success rate of hatchlings and importantly human interference. However in a new study from the University of Glasgow researchers have taken a closer look at the often ignored post-nesting behaviours of female turtles, after they have buried their babies, but before they return to the sea. In doing so they have uncovered a potential new behaviour in some species whereby mothers create ‘decoy nests’ surrounding the real thing. So just what does this new behaviour really involve and are they actually creating decoy nests or just disguising their own?

Scattering the sand

This new study, recently published in the Royal Society Open Science journal, was carried out by researchers from the natural history department at the University of Glasgow. It focuses on data collected on nesting beaches in Trinidad between 2013 and 2019, regarding the post-nesting behaviour of hawksbill and leatherback turtles. In doing so they found that, unlike most other turtle species, these two weren’t making a beeline for the ocean when they had laid their eggs, but continuing to stick around and more importantly keep working. This could last for up to 30 minutes and involved females ranging several feet in random directions to different spots surrounding their nest. At these spots or ‘stations’, of which there could be between two and twelve for each turtle, they would continue to dig and or scatter sand with their flippers replicating the types of patterns in the sand you would find directly over a nest.

hawksbill sand scattering
A hawksbill turtle engaged in the sand scattering behaviour associated with these decoy nests

Decoy v disguise

The researchers believe that the purpose of this behaviour is to create ‘decoy nests’ around their own eggs to throw off predators and increase the chances of their eggs surviving to hatch. Senior author Dr Malcom Kennedy told BBC’s Science Focus that “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 makes a lot of sense as the best way to hide something is often amongst similar objects or places, and means that predators such as seabirds, mongooses, dogs and wild pigs (all egg predators in Trinidad) often give up after multiple failed digs. Because of the fact that these two species share a common ancestor around 100 million years ago, Kennedy also suggests that these decoy nests could have been going on since the age of dinosaurs.

leatherback hatchling
A leatherback hatchling climbs over his siblings’ eggs

However some researchers aren’t so quick to agree with Kennedy and his colleagues from Glasgow. Some sceptics believe that the large size of the turtles, in particular leatherbacks, could mean that the researchers were reading too much into each minute movement and adding motivations for this accordingly. Others agree that this behaviour is new and involved in nest protection, but suggest the sand scattering could just be to generally disguise the nests and not necessarily to create decoys. Other turtle researchers like Alexander Gaos, speaking to New York Times, believe that “whether you call it decoy or a disguise, it’s still the same activity”.

Protective mothers

Regardless of whether these turtles are disguising nests or creating decoys, there is little doubt that the intention behind the behaviour is nevertheless to increase their offspring’s chances of survival. We know this because any sand scattering done by hawksbills of leatherbacks, in between laying their nests and returning to the sea, is extremely energy consuming and increases their own chances of being predated upon. Therefore it only really makes sense for them to be doing this if there is some significant survival advantage to their offspring. However, given the endangered status of both species, it is important that we learn more about this behaviour and how it aids reproductive success in order to ensure we can help fully protect them.

hawksbill hatchlings
For turtle mothers all the extra work of decoys and disguises is worth it if their offspring benefit

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