Sound production in sea turtle nests and hatchlings (Eretmochelys imbricata and Caretta caretta) in Northeast Brazil

Sea turtles have been considered the least vocal of living reptiles, but recent studies are changing this perception. Here, we aimed to investigate the acoustics of hatchlings of, Eretmochelys imbricata and Caretta caretta in Northeast Brazil, to describe their acoustic signals and compare sound structure within and between species. We monitored 13 km in Ipojuca, southern coast of Pernambuco State. We recorded five nests of each species and the hatchlings' walk to the sea in 2020/2021. We recorded 12 sonotypes in C. caretta and 5 in E. imbricata, increasing the number of described signals. Nevertheless, not all sonotypes were produced by all or in the different developmental stages. Some of the sounds for both species reached ultrasonic frequencies. The sound structure varied between C. caretta nests, suggesting a potential vocal signature, but the sound structure had no variation between E. imbricata nests. The sound structure varied between species. Despite their reputation for being silent, this study shows a diverse acoustic repertoire in the target species, further supporting speculations of acoustic signals mediating the potential synchronisation of hatchlings' departure to the sea. Our signal descriptions could be used for future passive acoustic monitoring of the target species. Future studies should focus on understanding the functionality of acoustic signals in the different life stages.

Automated summary

Acoustic studies on sea turtles in Northeast Brazil reveal variations in sound structure between species and nests, challenging the perception that sea turtles are silent. The diverse acoustic repertoire of sea turtles supports the hypothesis that acoustic signals may play a role in synchronizing hatchlings' departure to the sea. Further research is needed to understand the functionality of these acoustic signals.