Radiated tortoise

The radiated tortoise is threatened by the illegal pet trade, but you can help by being a responsible pet owner and not supporting this trade and discouraging friends and family from doing so.

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Physical features

Radiated tortoise weight range for males is 10-23 lbs, average 15 lbs. For females, range is 7-22 lbs., average is 12 lbs. The largest known radiated tortoise was a female that weighed 55 lbs.
Radiated tortoise carapace length for males is 11-15½ inches, average 13 inches. For females, range is 9½-14 inches, average 12 inches.
Slight sexual dimorphism is usually visible by the time a male reaches a carapace length of 12-14 inches (26 cm). Differences include a generally longer tail and a more noticeable notch in the plastron below the tail for males. Males also have very concave plastrons to allow for mounting of the females.
Radiated tortoises possess the typical tortoise body plan including a high-domed carapace and elephant-like feet.
They have yellow markings on their legs, feet, and head and yellow lines that radiate from the center of each scute, giving the tortoise its name. Their pattern helps to camouflage them among the leaf litter and thorn scrub shade.
The shell is supplied with blood vessels and nerves so, like other tortoises, it can feel when it is being touched. The tortoise’s ribs and spines form the shell, as with all other turtles and tortoises. The scutes covering the shell are made of keratin.

Range and Habitat

Range – extreme southern and southwestern part of the island of Madagascar and has been introduced to the islands of Réunion and Mauritius
- - They are estimated to have a total population range of 6,200 sq. miles (10,000 km) and are extinct from at least 40% of their historic range.
Habitat – dry spiny forests and areas with low irregular rainfall. They are also found on high inland plateaus and sand dunes along the coastline.

Diet: Herbivore

Wild – Grazing constitutes 80-90% of their diet, while they also eat fruits and succulent plants.
- - A favorite meal item in the wild includes the Opuntia cactus, an introduced species, and they will eat cacti pads including the spines.
  - Radiated tortoises typically graze in the same area, preferring the high-protein, low-fiber content of new growth to the less tasty mature growth. This keeps plants closely trimmed.
  - They will occasionally eat droppings from other animals and pieces of bone and mollusk shells, which is thought to add calcium and minerals to their diet.
Zoo – mostly leafy greens with some other vegetables mixed in (squashes, carrots, etc.), hay, tree leaf and grass browse
Radiated tortoises can “drink” water through their nostrils. This is an adaptation that allows them to obtain water from shallow pools of water in an arid climate. They are unable to close their nostrils, however, in the same way that an Aldabra tortoise can.

Lifespan

Wild – have been known to live up to 100 years
Zoo – possibly around 100 years
- - Radiated tortoises have only been kept in zoos since the late 1960s, and we need more data about lifespan for both wild radiated tortoises and tortoises in human care.
  - One individual at Zoo Atlanta arrived in 1969 and was estimated to have hatched in 1954. Another individual may have hatched as far back as 1946. In 2023, that put these individuals at minimum 69 and potentially 77 years old, respectively.
These tortoises commonly live over 100 years. The record was a female that lived to be 188 years old.

Reproduction

Male radiated tortoises are sexually mature at around 12 inches (31 cm); females typically take longer to reach sexual maturity and are often at larger sizes at first age of reproduction than males might be. Age at maturity is usually between 16-21 years.
The mating ritual consists of the male bobbing his head up and down and smelling the female’s legs and cloacal region. Vocalization by the male is also common.
Females can produce 1-3 clutches per breeding season with 1-5 eggs per clutch.
Females use their back legs to dig a nest 6 to 8 inches in the ground, lays her eggs, and after burying them, she leaves the nest site.
Incubation usually lasts between five and eight months, often including a period of “diapause” when the eggs stop developing for a time during incubation.
Hatchlings are around 1¼ inches to 1½ inches long and do not have the radiated or star pattern of the adults. They are usually pale yellowish with black markings.
When they first emerge, hatchlings have flatter shells but they become more dome-shaped as they grow.

Conservation: Critically Endangered

What’s the Issue?

In Madagascar, slash-and-burn agriculture and mining have diminished habitat for this critically endangered tortoise
An estimated 200,000 radiated tortoises are poached from the wild annually for the illegal pet trade and meat.
It is estimated the radiated tortoise could be extinct in just 10-20 years due to current threats.

How does This Affect Humans?

The tortoise is considered sacred by some of the local tribes (Mahafaly and Antandroy), so they hold an inherent importance to many local people. The ‘fady’ or taboo associated with the tortoises, however, is losing some of its strength in some younger generations as some traditional beliefs are less tightly-held.
The radiated tortoise is considered a flagship species for the spiny forests of southern and southwestern Madagascar. Its conservation is linked to the conservation of many other endangered species, including plants.
Excerpt from the SAFE program 2018 plan: The Radiated Tortoise is one of Madagascar’s most iconic and culturally significant species. It’s also the flagship species of the critically endangered spiny forest ecoregion along the southern most region of the island Consequently, conservation efforts for the Radiated Tortoise will also benefit other key species including endangered lemurs, reptiles, invertebrates and vegetation.

What is Zoo Atlanta Doing to Help?

Zoo Atlanta supports radiated tortoise conservation efforts through Turtle Survival Alliance’s Radiated Tortoise Reintroduction Program through our Quarters for Conservation 2019-2020 project cycle. In 2018, unprecedented confiscations of over 18,000 radiated tortoises were rescued and are cared for by the Turtle Survival Alliance. The Radiated Tortoise Reintroduction Project’s goal is to reintroduce these poached tortoises back into the wild into safe and suitable habitats with the support and involvement of local people.
Zoo Atlanta’s radiated tortoises are part of a Species Survival Plan, which maintains genetic diversity of a particular species within a zoological population.

What Can You Do to Help?

You can help save radiated tortoises by not participating in the illegal pet trade and discouraging friends and family from doing so.
The radiated tortoise is nationally protected under Malagasy law and internationally protected under CITES Appendix I.

Interpretive Information

When caught, this tortoise emits high-pitched cries, sometimes for as long as an hour after capture. This loud noise would startle a predator and it would potentially give up
In southern Madagascar, radiated tortoises are known as “Sokakes”.
When radiated tortoises feed on prickly pears, an invasive plant that grows rampant in Madagascar, the dark red fruit leaves a stain on their mouth that looks like lipstick.
The radiated tortoise Species Survival Plan was created in 1985 at the Bronx Zoo and was one of the first SSPs to be created for a reptile.
Radiated tortoises avoid activity during the hottest part of the day and are most active in the morning and late afternoon.

References

Bonin, F., Devaux, B., & Dupre, A. (2006). Turtles of the World (2006 ed.) (P. C. Pritchard, Trans.). Baltimore, MD: The John Hopkins University Press.
Kirkpatrick, D. T. (1992, March/April). The Radiated Tortoise. Reptile & Amphibian Magazine, 18-24.
Leach, K. (2018, December 4). Quarters for Conservation Proposal: Radiated Tortoise [PDF]
Leuteritz, T. & Rioux Paquette, S. (Madagascar Tortoise and Freshwater Turtle Red List Workshop). 2008. Astrochelys radiata. The IUCN Red List of Threatened Species 2008: e.T9014A12950491. https://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T9014A12950491.en. Accessed on 16 November 2023.
Pritchard, P.C.H. 2013. Madagascar: Island continent of tortoises great and small. In: Castellano, C.M., Rhodin, A.G.J., Ogle, M., Mittermeier, R.A., Randriamahazo, H., Hudson, R. and Lewis, R.E. (Eds.). Turtles on the Brink in Madagascar: Proceedings of Two Workshops on the Status, Conservation, and Biology of Malagasy Tortoises and Freshwater Turtles. Chelonian Research Monographs 6: 17-24.
Radiated Tortoise AZA Regional Studbook (2019) accessed 16 November 2023
Radiated Tortoise. (n.d.). Retrieved May 28, 2019, from https://www.hoglezoo.org/meet_our_animals/animal_finder/radiated_tortoise/
Radiated Tortoise. (n.d.). Retrieved May 28, 2019, from https://nationalzoo.si.edu/animals/radiated-tortoise
Radiated Tortoise SAFE Program Plan 2018. (n.d.). Retrieved May 28, 2019, from https://www.speakcdn.com/assets/2332/radiated_tortoise_safe_species_program_plan_16_september_2018.pdf
Turtles on the Brink in Madagascar: Proceedings of Two Workshops on the Status, Conservation, and Biology of Malagasy Tortoises and Freshwater Turtles. Christina M. Castellano, Anders G.J. Rhodin, Michael Ogle, Russell A. Mittermeier, Herilala Randriamahazo, Rick Hudson, and Richard E. Lewis, Eds. Chelonian Research Monographs (ISSN 1088-7105) No. 6, doi: 10.3854/crm.6.a12p59 • © 2013 by Chelonian Research Foundation, Lunenburg, MA, USA. Published 30 October 2013
Zoo Atlanta Animal Care Team

Updated September 2024

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