Why do turtles bask in the sun?

A bale of painted turtles bask in the sun. A group of turtles is called a bale, nest, turn or dole.

By Stacey Venzel

Tourists roll out beach towels to soak up the sun’s rays in an effort to catch a tan. Turtles, however, have a physiological reasoning for sunbathing.

Because they are cold-blooded, the body temperature of a turtle depends on its environment. Especially prevalent in aquatic turtles, land basking and water basking helps turtles absorb heat from the sun through their body, but basking has other added benefits too.

LAND BASKING

Whether finding a raft to perch on or laying out on the shore, turtles have their ways of optimizing sunlight exposure. Commonly, aquatic species, like the savannah side-necked turtle, swarm together on logs or edges of the pond to gather some heat. Green sea turtles in Hawaii are known to come ashore to bask, an unusual venture because the species is only otherwise known to come on land to lay eggs.

WATER BASKING

Solar absorption can also occur in the water. At shallow depths, the sun’s rays can reach a turtle underwater. Other turtles, like loggerheads, might engage in surface basking, floating for more direct sun exposure. Some species, like the mud turtle and leatherback, rarely bask.

A heat lamp is important equipment for any people who have turtles as pets.

PET TURTLE BASKING

For pet turtle owners, it is important to provide means for internal temperature regulation in these cold-blooded animals. Heat and UV lamps are vital attachments to turtle enclosures, shining on land or water or perhaps on a floating perch, depending on the species.

OTHER REASONS FOR BASKING

Turtles that bask on land are also gaining heat from the substrate they are in contact with, such as a log or the sand, through a process known as conduction. This is especially true of aquatic animals who come out of the water to absorb heat, as absorption is more difficult in water, a compound that instead of sharing heat, likes to keep it for itself.

A closeup of an ectoparasitic growth on the shell of a turtle, in this case, a barnacle. Basking in the sun allows turtles to dry their shell in the sun, which prevents parasites from attaching.

Additionally, hanging out in the sun helps these turtles produce vitamin D, an essential nutrient for healthy living. Certain artificial lighting can help the body synthesize vitamin D, which is why UV lamps are important in indoor pet turtle homes not exposed to natural sunlight.

Basking can also help relieve an animal of ectoparasites, the scientific term for harmful organism’s on the outside of an animal. Leeches are a blood-sucking ectoparasite that can cause anemia in reptiles. Drying out in the sun causes the leeches to shrivel up and die. Algae on basking aquatic turtles can also dry out and fall off, allowing the shells to retain their aerodynamic nature.

Sources:

Stephen Divers, Doug Mader, Current Therapy in Reptile Medicine & Surgery, (St. Louis, Elsevier Saunders, 2014), 2, 72.

Karen Eckert, David Gulko, Sea Turtles: An Ecological Guide (Honolulu, Mutual Publishing, 2004), 56-57.

Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 27-28.

Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009), 49.