Warm Sands, Faster Hatchlings: Sea Turtle Nests Run Hot in Ghana

On a stretch of palm-fringed coastline in Ada Foah, Ghana, olive ridley sea turtles have been laying their eggs for generations in the sands of the Songor Ramsar Site and UNESCO Biosphere Reserve. What happens beneath that sand in the weeks that follow—the slow, hidden chemistry of embryonic development—has long remained a mystery in West Africa, one of the least studied regions for sea turtle reproduction. Now, a team of researchers from the University of Ghana has provided the first detailed in situ portrait of the thermal world inside olive ridley nests at this major rookery, and their findings carry a warning written in degrees: nest temperatures at the site are hot enough to accelerate development, stress developing embryos, and likely tip hatchling sex ratios heavily toward females.

The study, published in the journal Discover Conservation, monitored seven olive ridley nests during the 2020–2021 nesting season, which runs from September through January in Ghana. Researchers led by Baidoo Abigail, Addo Samuel, and Agyekumhene Andrews deployed miniature HOBO U22 temperature data loggers directly into egg clutches as females were laying, positioning the devices near the center of the clutch where metabolic heat accumulates most. A second logger was buried roughly two meters from each nest at identical depth, acting as a control that recorded the background temperature of the surrounding beach sand. Both loggers recorded measurements every fifteen minutes for the entire incubation period, generating an unusually high-resolution record of the thermal environment experienced by developing embryos.

The most striking result concerns the moment when nest and sand temperatures part ways. For the first nineteen days of incubation, temperatures inside the eggs and in the adjacent sand tracked each other closely, with no statistically significant difference between them. But from day twenty onward—the period that coincides with the thermosensitive window during which hatchling sex is determined—nest temperatures rose consistently above sand temperatures and stayed elevated until the hatchlings emerged. The researchers attribute this divergence to metabolic heating: as embryos grow, their collective metabolic activity generates heat that warms the clutch from within, a phenomenon well documented in sea turtles but never before quantified at this West African site.

The numbers reveal how warm this rookery already runs. Mean nest temperatures across the seven nests ranged from 30.7 to 33.3 degrees Celsius, averaging 32.4 degrees, while adjacent sand temperatures averaged a cooler 31.7 degrees. When nest and sand temperatures diverged, the difference typically spanned 0.3 to 1.7 degrees Celsius, averaging about 0.9 degrees. These figures matter enormously because olive ridley turtles exhibit temperature-dependent sex determination: pivotal temperatures that produce equal numbers of males and females have been reported near 30.0 to 30.5 degrees Celsius, with anything warmer producing females. Since mean nest temperatures during the middle third of incubation—the critical sex-determining window—ranged from 31.5 to 32.9 degrees, the researchers conclude that the monitored nests exceeded pivotal thresholds for a substantial portion of development, strongly implying a female-biased hatchling output. Although sex ratios were not measured directly, the thermal signature alone is telling.

Temperature exerted its clearest influence on the pace of development. Incubation duration ranged from 45 to 57 days across the seven nests, averaging about 48 days, and was strongly and negatively correlated with mean nest temperature, with a correlation coefficient of minus 0.88. Warmer nests hatched markedly sooner, and mean nest temperature explained roughly 78 percent of the variation in incubation duration among nests. This relationship is among the most robust in reptilian developmental biology, but its confirmation in Ghanaian sands underscores how powerfully thermal conditions govern the timeline from egg to emergence, even across a modest sample of nests.

Perhaps surprisingly, temperature told a much weaker story about reproductive success itself. Hatching success ranged widely, from 53.4 to 95.5 percent, with a mean of 81 percent, and emergence success ranged from 44.3 to 92.9 percent, averaging 75.2 percent. Yet neither measure showed a meaningful correlation with mean nest temperature, and incubation duration likewise bore no relationship to success rates. The authors interpret this variability as evidence that factors beyond temperature—sand moisture, gas exchange within the nest chamber, beach compaction, and disturbance—interact in complex ways to determine whether embryos survive. The finding is a caution against attributing nest outcomes to temperature alone, particularly in natural environments where multiple stressors overlap.

The hatchlings themselves offered additional clues about thermal stress. Morphological abnormalities, most frequently non-uniform carapace development, were observed in hatchlings from nests with mean temperatures ranging from 32.6 to 33.2 degrees Celsius, and the two hottest nests, averaging 33.0 and 33.2 degrees, produced the greatest number of anomalies. Locomotor performance, assessed through a self-righting test in which hatchlings were placed upside down on moist sand and timed as they flipped themselves upright, showed a moderate association with nest temperature, though the relationship did not reach statistical significance in the small sample. Such performance traits are closely linked to post-emergence survival, since hatchlings that cannot right themselves or crawl quickly are more vulnerable to predators on their frantic dash to the sea.

The study also carries practical implications for how scientists model the future of sea turtle populations under climate change. Many recent studies estimate nest temperatures from sand temperature data by adding a correction—typically 0.5 to 1.0 degrees Celsius—to account for metabolic heating. The Ghanaian measurements, showing an average nest-to-sand difference of about 0.9 degrees during divergence, provide direct empirical support for the magnitude of such corrections at a tropical site where incubation temperatures already press against pivotal thresholds. The researchers note that the beach at Songor was artificially nourished in 2010 as part of coastal erosion mitigation, a process known elsewhere to alter sand thermal properties, though sediment characteristics were beyond the scope of this study. With global climate change projected to raise sand temperatures further, and with local coastal development reshaping nesting microclimates, accurate in-nest measurements will become ever more critical for forecasting sex ratios and hatchling survival.

The work is not without limitations. Seven nests constitute a small sample, spanning a single nesting season, and the statistical power to detect subtle relationships was correspondingly limited; tendencies toward cooler deeper nests and warmer larger clutches matched published patterns but did not reach significance. Fine-scale thermal gradients within clutches were not assessed, and hatchling sex was never directly determined. Still, as the authors emphasize, this study delivers the first baseline characterization of olive ridley nest thermal dynamics anywhere in West Africa, filling a conspicuous geographic gap in global sea turtle science. As temperatures continue to climb at nesting beaches worldwide, understanding precisely what developing embryos experience inside their eggs—not just what the surrounding sand feels like—may prove decisive for conserving one of the ocean’s most vulnerable travelers, and for ensuring that Ghana’s beaches keep producing hatchlings capable of completing their ancient journey back to the sea.

Subject of Research: Effects of incubation temperature on olive ridley sea turtle nest success and hatchling development at the Songor Ramsar Site, Ghana

Article Title: Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana

Article References: Abigail, B., Samuel, A., & Andrews, A. (2026). Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana. Discover Conservation, 3(1), Article 40. https://doi.org/10.1007/s44353-026-00109-8

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00109-8

Keywords: olive ridley sea turtle, incubation temperature, metabolic heating, temperature-dependent sex determination, hatching success, Songor Ramsar Site, Ghana, climate change, nest temperature, hatchling performance, West Africa, conservation