Female green sea turtles migrate long distances to lay their eggs, often arriving at the same beach they hatched from. They dig out a nest in the sand, burying their eggs and then heading back to the water. These eggs will hatch, usually at night, in large groups. This synchronous hatching was thought to be a way to increase the odds of at least a few of the turtles surviving their journey into the open ocean. In a paper just published in the Proceedings of the Royal Society B journal, scientists provide an explanation and evidence for why this synchronous hatching is so important.
Researchers from the University of Bristol and the Universidade Federal de Alagoas wanted to investigate whether the turtles’ strategy actually helped more hatchlings survive. They studied 33 green sea turtle nests, checking them every half hour throughout the night. On average, about 50 turtles would hatch per group. The researchers found that larger groups of hatchlings were at lower risk of predation. This wasn’t a case of more turtles surviving simply because there were more of them to begin with; hatchlings in larger groups were significantly less likely to fall prey to predators such as yellow crabs. Yellow crabs are nearly as small as the turtles so it takes them a long time to handle and consume a single hatchling. When a very large group of turtles hatched, the crabs remained occupied with the first prey they captured, allowing the rest of the hatchlings to make it to the water. By overwhelming their would-be predators, the hatchlings achieved an attack abatement effect and were more likely to survive.
Until this study, there was no clear evidence for why sea turtles hatch simultaneously in large groups. Approximately 1% of hatchling green sea turtles will survive to adulthood so strategies that reduce predation are especially important. The researchers hope that these findings will lead to further studies on how these tactics evolved in turtles and other animals.
Robson, S, Pinheiro, H, Martins, A, Riul, P, Bruno, S, Janzen, F & Ioannou, C. The anti-predator role of within-nest emergence synchrony in sea turtle hatchlings. Proceedings of the Royal Society B: Biological Sciences (2016).