Sea turtles are responding to climate change by nesting earlier in the year in a move to compensate for rising temperatures, researchers monitoring the breeding habits of green and loggerhead turtles in Cyprus have discovered.

Observing the ‘natal philopatry’ common in sea turtles – a kind of homing system which sees them return to nest in the area where they themselves hatched – a research team from the University of Exeter witnessed a changing behaviour in nesting over the last three years.

The temperature plays a crucial role in the sea turtles’ nesting and hatching process. In these species, temperature determines the biological sex of offspring, with more females born when it’s warmer, and affecting the hatching success rate when it gets too hot.

Using three decades of data and more recent observations, the research team – comprising those from University of Exeter and the Society for the Protection of Turtles – now predicts that by the year 2100, there will be ‘hardly any new loggerhead turtle offspring produced, unless these turtles counter the higher temperatures by moving their nesting season forward.

After placing temperature loggers into nests at night when the females are laying their eggs, and retrieving them once the nest hatches, the researchers estimated that the turtles need to nest 0.5 days per year earlier to maintain the current sex ratio.

However, to prevent egg hatching failures, they will need to get started even earlier; some 0.7 days per year earlier.

It’s a necessity that – it would seem, as indicated by the data gathered – sea turtles are already attuned to, with loggerhead turtles indeed already nesting earlier in the year, with returning females advancing the start of nesting by 0.78 days per year since 1993.

What this means is that, for now at least, the turtles are doing enough to ensure their eggs continue to hatch by nesting earlier in more ideal temperatures.

Professor Annette Broderick, said: “This is a bit of good news, as we’ve shown that these turtles are responding to the elevated temperatures brought about by climate change by shifting to cooler months to nest.

“There is no guarantee that they carry on doing this, though – it’s very much dependent on how much the temperature rises, and also what they are eating. If the timing of production in terms of where their food’s coming from shifts, then they could start to be disconnected ecologically between where they forage and where they breed.”

Using data from across 31 years of observation of more than 600 individual green turtles at the same beach in North Cyprus, the research team has also published a study into what is influencing when they start laying each year, and how we can explain the advancement in nesting times over the past three decades.

It found that individual turtles were adjusting the timing of nesting based on sea temperature, laying eggs 6.47 days earlier for every 1°C increase in ocean temperature. It was calculated that temperature accounted for around 30% of the advancement, with more experienced females and those laying more clutches also nesting earlier.

“To know if the advancement we see now will continue into the future, it is crucial to understand the combined effects of changes in, for example, the age structure of the population, and how individual turtles respond to environmental change,” said the study’s lead author, Mollie Rickwood, from the University of Exeter’s Centre for Ecology and Conservation.

Dr Damla Beton, from the Society for Protection of Turtles, added: “Although our turtles appear to be coping with current rising temperatures, it is unclear how long they may be able to do this before conditions in Cyprus are no longer suitable, but cooler locations in the Mediterranean may become available to them to nest.”

The two studies have been published separately this month. ‘Phenological shift mitigates predicted impacts of climate change on sea turtle offspring’ has been published in the scientific journal, Endangered Species Research.

‘Individual plasticity in response to rising sea temperatures contributes to an advancement in green turtle nesting phenology’ has been published in the journal Proceedings of the Royal Society B.

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