Endangered Species Spotlight: Dahl’s Toad-headed Turtle

IUCN Red List Status (2021): Critically Endangered

Our Endangered Species Series educates the masses about some of the rarest and most threatened species living in tropical forests. Today, we meet Dahl’s Toad-headed Turtle, a small freshwater reptile known for its big head and even bigger smile. Discover this elusive little creature alongside biologists and environmentalists as they race to generate knowledge and protect the future of this critically endangered species.

Introducing Dahl’s Toad-headed Turtle

Considered to be small-to-medium sized, one of Dahl’s Toad-headed turtles’ key features is their large head shape and size, which is, on average, one-fourth the size of their shell! The shell itself is roughly 300mm (11.5in) long. Their neck is long and thin, with gray or black stripes passing along the neck, through the eyes, and up into the nostrils. Males have additional red markings along their neck, throat, and front scales. Females tend to be larger than their male counterparts but possess a shorter, weaker tail.

They are omnivores, surviving on a diverse diet of ants, aquatic insects, crabs, crustaceans, frogs, plant material, small fish, snails, tadpoles, and occasionally, carcasses. This diet means they must stick relatively close to water sources within the forest. Given Colombia’s proximity to the Equator, a wet and dry season rules their environment. It is suspected that these turtles move on land during the dry season. Nesting, reproduction, and a period of estivation are speculated to occur during the dry season (estivation is the same thing as hibernation, just in the summer).

Dahl’s Toad-headed Turtle is a relatively recent scientific find. Professor and marine biologist George Dahl first documented this reptile in 1958. Both the common name and the scientific name, Mesoclemmys dahli, honor this turtle’s discoverer.

These creatures can be difficult to find in the wild. There have been less than 10 recorded sightings from their initial documentation until the turn of the 21st century. Even more surprising, all early sightings occurred within a single region of Colombia called Sucre. Biologists combed identical habitats along Colombia’s Atlantic coast but went decades without success. More recently, there have been sightings in neighboring regions of Sucre, which means there are other individuals out there who are just extraordinarily difficult to find. This difficulty in finding wild specimens means we have little historical or current information about these reptiles.

In 2015, the Wildlife Conservation Society (WCS) and the Turtle Survival Alliance (TSA) came together to find and document as much information as possible about this little reptile. Their foundational study provided much insight and also identified significant knowledge gaps. Teaming up with the Rainforest Trust in 2019, these three organizations created the first protected area, Reserva Natural La Carranchina, for these reptiles and other endangered animals in northern Colombia. Under these monitored conditions, we’re learning more about them and uncovering an extremely threatened existence.

Deforestation and Diminished Gene Pools

Since the TSA and WCS set out to learn more about the Dahl’s Toad-headed turtle, they’ve only been able to locate 131 individuals throughout Colombia’s Atlantic Coast. To avoid double counting and learn more about the turtles’ genetic makeup, the WCS took blood samples from each individual. These blood tests revealed a dangerously high level of inbreeding among the four known population clusters. This small gene pool can cause health and fertility problems for future generations. In response, the TSA and its partners are developing a genetic rescue strategy to help the species rebound. The Reserva Natural La Carranchina will act as a recovery ground, in which scientists can bring together unrelated individuals to create more genetic diversity (=healthier turtles!).

This internal genetic threat is the result of external human behaviors. The TSA and WCS-Colombia found that these reptiles’ habitat range is very small, estimated to be around 31 hectares. If you’re more of a visual person, below is an illustration of this habitat range relative to the South American continent.

Only 8% of the dry tropical forests of this habitat range remain intact, making the Dahl’s habitat one of the most degraded ecosystems in the country. This diminished range is largely attributed to habitat fragmentation and land use conversion. This phenomenon likely also caused the reduction of genetic diversity — as the forest became more fragmented, population clusters were cut off from one another.

Fun fact: Locally, they’ve earned the name tortuga montañera (mountain turtle), referring to its habit of walking in higher areas that do not flood.

Race To Save Disappearing Habitat

Further study of the Dahl’s Toad-headed Turtle is needed as little is known about the species outside of their physical appearance and diet. Scientists are still unsure when or how often reproduction occurs, whether they are most active at night or during the day, and what makes their habitat suitable. Nevertheless, the heavily fragmented habitat and a known population of under 200 individuals make Dahl’s Toad-headed Turtle critically endangered. For those unfamiliar with the IUCN Red List Categories, the next step up from this designation is extinct in the wild — a status we do not want to reach.