Turtle Talk: What Do Their Sounds and Calls Mean?

Turtle sounds range from mating calls to defensive hisses, and while it's clear that different sounds serve different purposes, what exactly are turtles trying to say with their various vocalizations? Turtles make grunting, clucking, or chirping noises when mating, hissing to warn off predators, bellowing to attract mates, and squeaking sounds from hatchlings to signal distress to their mothers.

We'll take a deep dive into the most up-to-date scientific studies that have investigated the meanings and purposes of the many sounds that turtles make. By looking at ethological research that has documented turtle behavior, acoustic research that has analyzed turtle sounds, and physiological research that has looked at the biological processes that make turtle sounds possible, you'll come away with a better understanding of the many ways turtles can communicate.

The Diverse Repertoire: Exploring the Different Sounds Turtles Make

From grunts and chirps to bellows and hisses, turtles produce a surprisingly wide range of vocalizations. In fact, biologist Gabriel Jorgewich-Cohen has recorded over 50 turtle species making sounds that include croaks, clicks, purrs, and coos. Some species have been shown to have as many as 30 different call types.

Vocalizations have been observed in both aquatic and terrestrial turtles, although the sounds they make can vary. For example, sea turtles make cries that are audible underwater, while terrestrial species like the red-footed tortoise make grunting sounds during mating. In addition, age and sex differences have been observed in turtle vocalizations, with a study of Chinese striped-neck turtles showing that adult females made more high-frequency calls than males.

This diversity of vocalizations is thought to have evolved to help turtles communicate with one another, establish territories, attract mates, and coordinate with their parents and offspring. Jorgewich-Cohen noted that turtles made different calls when they were alone, with same-sex or mixed-sex groups, and when they were courting. In general, the more social a species, the more diverse its vocal repertoire.

These findings have turned the traditional idea of turtles as silent animals on its head. Instead, their diverse vocalizations demonstrate a surprising level of complexity and offer a window into the early evolutionary history of vertebrate vocal communication. But what exactly do turtles communicate with their wide range of vocalizations?

Functional Vocalizations: What Turtle Sounds Are Telling Us

Turtles’ wide range of vocalizations are used for many different purposes, including mating, territoriality, and parent-offspring interactions. One study even found that the more social a species of turtle is, the more diverse its vocal repertoire.

For instance, a study of Chinese striped-neck turtles discovered that adult females made more high-frequency calls than males, which the researchers suggested was a way to indicate their reproductive state. Meanwhile, a study of the giant South American river turtle found that both hatchlings and adults used vocalizations to help coordinate mass migrations.

It’s possible that aquatic turtles rely more on underwater vocalizations, while terrestrial turtles use vocalizations for mating and territorial displays above water. One group of researchers even suggested that hatchlings may use vocalizations and body contact to coordinate their exit from the nest. The evolution of these different vocal abilities likely helped turtles in a variety of ways in their environments and social groups.

Vocal Variations: Differences in Turtle Vocalizations Between Species

Turtles have shown a wide range of vocal repertoires, and these repertoires have been shown to differ significantly between species. For example, a study of the Chinese striped-neck turtle (Mauremys sinensis) found that adult females had more high-frequency call types than adult males, which the researchers suggested was a way for the females to indicate their reproductive state. Meanwhile, a study of the Chinese soft-shelled turtle (Pelodiscus sinensis) found that this species, which is highly aquatic, had up to 10 call types, four of which were multi-harmonic vocalizations.

The vocalizations of aquatic and terrestrial turtles have often been shown to be shaped by the demands of their environments. For example, a study of the Chinese soft-shelled turtle found that highly aquatic turtles that live in deep water, such as the Amazon river turtle (Podocnemis expansa) and the long-necked turtle (Chelodina oblonga), have more call types and more harmonic vocalizations, which the researchers suggested may help them communicate more effectively in their underwater habitats. Meanwhile, a study of two species of freshwater turtles found that females had lower-frequency vocalizations than males, which the researchers suggested may help them with territorial and mating displays when they're out of the water.

The differences in turtle vocalizations are likely the result of a combination of environmental, behavioral, and evolutionary factors. By studying these differences between species, researchers can learn more about the adaptive value of vocal communication in turtles and gain a better understanding of the evolution of acoustic signaling in vertebrates.

Vocal Ontogeny: How Turtles' Vocalizations Develop

Turtle vocalizations aren’t just limited to adulthood - they actually start communicating acoustically from the moment they’re born. Research on the giant South American river turtle (Podocnemis expansa) found that the turtles’ hatchlings vocalize while they’re still in their eggs, and continue to do so as they leave their nests and head to the river.

These early vocalizations seem to help coordinate the turtles’ mass migrations, as other research found that adult female turtles are attracted to and respond to the sounds of their offspring. As turtles grow, their vocalizations and the sounds they make change in a number of ways.

A review of reptile vocalization noted that the turtle middle ear is more sensitive to underwater sounds, which suggests that the functions of their vocalizations change as they grow - with lower frequencies used for long-distance communication during migration, and higher frequencies used for short-distance communication during activities like nesting. Meanwhile, research on the Western Australian longneck turtle found that the species has a varied vocal repertoire that includes 17 different call types, from clicks and chirps to grunts and howls.

The ontogeny of turtle vocalizations can help us better understand where these reptiles’ acoustic communication comes from. By learning more about how turtles’ vocalizations develop from before they’re born to adulthood, we can also learn more about the specific adaptations that have made turtles such skilled communicators.

Evolutionary History of Turtle Vocalizations

The most recent evidence suggests that the vocalizations of turtles may have evolved much earlier in the vertebrate lineage than previously believed. A study in Nature Communications proposed that acoustic communication in vertebrates originated over 400 million years ago during the Devonian Period.

This contrasts with the long-held view that vocal communication evolved independently in different lineages. Instead, the data shows that the ability to vocalize can be traced to a common vertebrate ancestor. The study's authors even suggested that many animals previously thought to be "mute," including turtles, have a rich vocal repertoire.

Turtles have several unique adaptations compared to other reptiles that may have enabled the evolution of vocal communication. One study noted that turtles have well-developed middle ears and large tympana that are especially sensitive to underwater sounds, which would have made them well-suited to communicate in aquatic environments. This specialization in their anatomy would have provided social and survival benefits.

The widespread vocal abilities of vertebrates, including turtles, have important implications for our understanding of the origins and evolution of animal communication. As we continue to learn more about the many sounds made by these reptiles, we may also learn more about the selective pressures that led to the evolution of this important behavior.

Conclusion: The Surprising Voices of Turtles

The latest research has revealed a surprising complexity to turtle vocalizations, overturning the traditional notion of these reptiles as largely silent creatures. Turtles produce a diverse repertoire of sounds, including grunts, chirps, bellows, hisses, and even purrs, serving a variety of functions like mating, territoriality, and parent-offspring communication.

These findings challenge our understanding of the evolutionary origins of vocal communication, suggesting that the ability to vocalize may have emerged much earlier in the vertebrate lineage than previously thought. Turtles' unique anatomical adaptations, like sensitive middle ears and large tympana, have likely facilitated the development of their diverse acoustic capabilities.

As we learn more about the rich world of turtle communication, we also learn more about the adaptive advantages that have helped these shelled reptiles survive and thrive. Understanding the surprising voices of turtles helps us appreciate the natural world more fully, realizing that even the most silent of creatures have complex abilities.