An Introduction to the Ingestion of Stones, Bones, Fossils and Soil by Turtles by M. A. Cohen hile firsthand observations animals. In a subsequent section neutralize toxic properties of Wof this phenomenon are of this article, instances of this plants, and to maintain of a healthy rare, the ingestion of external min- behavior from the research of the intestinal pH (acidity/alkalinity eral sources such as stones, bones, scientific community will be briefly balance). Turtles possibly absorb fossils, and soil by various turtle described. essential minerals such as calcium species has been documented Ingestion of soil (geophagy) and phosphorus from the swal- through field research, scat analy- Geophagy is a behavior known in lowed stones. sis, and radiography. humans and other animals. As a tra- Gastroliths Some turtle keepers may be unfa- ditional cultural practice, humans Composed of the Greek root words miliar with the behavior described consume soils for various reasons. gastro- , meaning stomach, and in this article, and some may think Pregnant women in some develop- -lith, meaning stone, the term "gas- this article refers to bladder stones, ing countries believe nutrient-rich trolith" is generally defined as a with which many tortoise keepers soils are beneficial to their pregnan- stone retained within the gastroin- are familiar. To avoid ambiguity, it is cies, some religious observances testinal tract to aid in the digestion necessary to clarify the concepts. include the ingestion of soils, and, in of tough foods. Bladder stones, known to science areas of extreme poverty, residents Researchers document that some as uroliths, are formed internally may consume soils to supplement a birds, fish, and reptiles swallow and are composed of urates, i.e., meager diet. small stones to aid digestion. uric acid waste products. While the Researchers documenting the in- Researchers also document the exact cause of bladder stones is gestion of soils in turtle species ingestion of gastroliths by amphib- unknown, two factors—dehydration surmise that this behavior is pri- ians and crocodilians, theorizing and too much protein in the diet— marily for mineral supplementation. that, in these cases, the practice are suspected as contributing to Analysis of clay soils consumed by serves to control the animals' the formation of the uroliths. pregnant women in Africa reveals buoyancy. The focus of this article is exter- that these soils contain nutrients Gastroliths, also known as stomach nal mineral sources found in the critical to bone formation (Rosen- stones or gizzard stones, help to environment and ingested by the berg, 2018). Turtles may swallow grind tough food items like fibrous coarse soils such as sand for the vegetation and the hard shells same reasons they ingest small of seeds for herbivores that lack Terminology stones, i.e., for grinding tough foods, grinding teeth. Scientists have for controlling internal parasites, recorded the sizes of gastroliths geophagia (also known as and as a source of minerals. geophagy): ingestion of soil sub- ranging from sand particles to cob- strates, often those rich in clay Ingestion of stones blestones depending on the size of or limestone. Geophagy occurs in (lithophagy) the animal ingesting the gastrolith. humans and other animals, and Generally accepted is the fact Ingestion of bones and fos- reasons for this practice vary by that the herbivore diet comprises sils (osteophagy) species. vegetation and seeds that are dif- Calcium, a vitally important mineral lithophagia (a.k.a. lithophagy): ficult to digest because herbivores to turtle species, is essential for ingestion of small stones to aid typically lack grinding teeth. The normal skeletal and shell develop- digestion, among other probable ingestion of small stones that are ment. Turtles have exceptionally reasons. retained within the digestive tract high calcium requirements because assists in the breakdown of the of the amount of bone tissue in osteophagia (a.k.a. osteophagy): tough cell walls of certain foods, ingestion of bones and bone their bodies. Female turtles of rendering the nutrients within the reproductive age require additional fragments for purposes of miner- foods available to the animal. al supplementation. Osteophagy calcium during egg development provides additional calcium, According to Esque and Peters because both the egg yolk and the phosphorus, and other minerals (1994), other theories of stone egg shell are calcium-rich materials to an herbivore whose diet is ingestion include the following: (Yost et al., n.d.). typically low in these essential the presence of stones helps to Osteophagy is the most frequently minerals. control intestinal parasites, to observed of the three ingestion calcium, phosphorus, and other minerals. Desert tortoise Mineral ingestion behavior by the desert tortoise (Gopherus agas- sizii) is well-documented. Esque and Peters (1994) cite instances of mineral ingestion in wild des- ert tortoises, surmising that this behavior compensates for mineral deficiencies in desert soils and des- ert plants. While all desert tortoises require mineral macronutrients and micro- nutrients for optimal health, it is the young tortoises and the gravid females that have the greatest need for supplemental miner- als. Young tortoises need these nutrients for skeletal and shell development, and gravid females require added nutrients for egg development. Through their field studies in the Mojave Desert, Esque and Peters (1994) found that desert tortoises X-ray of a large, juvenile male desert tortoise, Gopherus agassizii, that swallowed ingested only white stones, not numerous small rocks. The tortoise was turned in to the CTTC Valley chapter by a private party, who had fed the tortoise a diet of kale, radicchio, and Mazuri pellets. gray, tan, or other colors. In the The private party kept the tortoise in an enclosure on a substrate of coconut fiber, Mojave, white stones are largely which the tortoise had apparently been eating. formed of caliche, also known as When the tortoise presented to the veterinarian, it was neither eating nor passing calcite, which is primarily composed feces. Dr. Kenneth Coscarelli of the Newbury Park Veterinary Clinic ordered a of calcium carbonate. diagnostic x-ray, and, following evaluation, recommended a treatment regimen. Desert tortoises have been known The treatment included the prescribed medications cisipride and metaclopramide, both of which are used to assist in emptying the stomach and assisting in intestinal to mine caliche soils for ingestion motility, plus soaks in warm water. purposes. Researchers R. W. Mar- The diet of the tortoise was also modified to include a chopped salad of organic low and K. Tollestrup observed dandelion greens, a very small amount of organic kale, with some organic iceberg female tortoises scraping away the for extra water. To increase the fiber, a small amount of soaked Mazuri pellets made topsoil to reach the caliche subsoil, into mush or soaked Bermuda grass hay pellet mush was mixed in with the greens. as documented in a paper published By the end of the first week of treatment, four small rocks were passed. It took in 1982. Subsequent research about two months total to get the rocks completely out. revealed that local desert tortoises As of mid-February 2019, this tortoise is in foster care awaiting adoption routinely visit caliche mines for pur- poses of mineral supplementation. behaviors in turtles, and is observed Instances of geophagy, Osteophagy in desert tortoises has in both wild and captive individuals. lithophagy, and osteophagy been observed in both wild animals Turtles ingest small bones, bone in turtles and captives. Tortoises ingest small fragments and fossilized bone to Box turtle whole bones from carrion and gnaw supplement their mineral needs. on weathered bones and even on Keepers of North American box Bones and fossils are rich sources the shells and bones of dead tor- turtles, Terrapene species, have of minerals, not only calcium and toises found in the wild (Esque and observed osteophagy in their pets phosphorus, but also trace minerals Peters, 1994). (Naish, 2014). Consuming bone including magnesium, manganese, fragments and gnawing on larger Galápagos tortoise potassium, selenium, boron, copper, bones supplement the omnivorous In her Ph.D. thesis, Dr. Linda Cayot zinc, and many others. diet of the box turtle with added (1987) refers to the scat analysis of Galápagos tortoise fecal material mammal hair, dried mammal and the finding that those analyses and reptile carcasses, as well as reveal the presence of soil particles mammal, reptile, and bird feces. and gravel in the scat of tortoises in His study also documented the an earlier study. ingestion of charcoal and sand Studies by Yost et al. (n.d.) indicate by the species. that the tortoises inhabiting the Mentioned in this study of radi- oldest, lowest-elevation Galápa- ated tortoise behavior is the gos islands are generally the fact that the leopard tortoise saddle-backed varieties that are (Geochelone [=Stigmochelys] usually smaller in overall size and pardalis) also engages in osteo- have thinner shells than their larger, phagy, according to a 1992 paper higher-domed counterparts from by S. J. Milton published in the islands with more humid highland Close-up of the stones that passed through the diges- South African Journal of Zoology. habitats. tive tract of the desert tortoise in the x-ray image on page 9. Photo by Karen Berry. Red-footed tortoise Depletion of calcium and other An omnivorous forest tortoise vital nutrients in the soils on the Hermann's tortoise endemic to northern South older Galápagos Islands account Documenting scavenging behavior Amer­ica, the red-footed tortoise for the fact that the saddle-backed by Hermann's Tortoise (Testudo (Chelonoidis carbonaria) consumes tortoises are smaller overall. Soils hermanni) in Serbia, Nikolić et al. more fruit than any other single in the humid highlands are more (2016) note that, while the spe- food item. Like many other tortoise nutritionally complete, therefore, cies is widely regarded as primarily species, however, the red-footed the tortoises in the humid highlands herbivorous, its diet also includes tortoise is an opportunistic feeder. grow larger because of their nutri- "mushrooms, soil, sand, pebbles, Wang et al. (2011) conducted stud- tionally superior foods (Yost et al., and animal matter," a fact con- ies of the species in the Pantanal, n.d.). firmed by several researchers. an enormous wetland region in Bra- Gopher tortoise Scientists confirm that Hermann's zil. Their research confirms that, in Native to the southeastern United tortoise also periodically ingests addition to fruit, flowers, and leaves, States, gopher tortoises, Gopherus soil—geophagy—for mineral the species also ingests a variety of polyphemus, are herbivores. Moore supplementation. other items, including invertebrates and Dornberg (2014) conducted T. hermanni also feeds on mammal such as ants, snails, and termites, studies of the species, concentrat- feces, apparently for the bone vertebrate carrion such as bones, ing on female gopher tortoises. The fragments and hair it contains, as egg shells, feathers, scales, and scientists used field observation, well as on carrion. Such "sporadical skin, fungi such as mushrooms and scat photography, analysis of scat carnivorous behavior" is consid- toadstools, and soils. samples, and radiography in their ered to be relic, and it requires Following scat analysis of samples research. additional investigation to better from both male and female red- Analysis of the gopher tortoise understand the ecological require- footed tortoises, Wang et.al. (2011) x-rays revealed that 85% of gravid ments of the species (Nikolić et al. identified vertebrate carrion in 25% females had stones, bones, bone 2016). of the females' scat though it was fragments, or seashells in their Radiated tortoise only 12.5% of their total intake. digestive tracts, while only 5% of While the radiated tortoise (Geo- One might conclude that females non-gravid females contained such chelone [= Astrochelys] radiata) is ingesting such mineral-rich items items. primarily herbivorous in its dietary as bones and egg shells could be choices, the species is an "opportu- related to reproduction, specifically These findings led Moore and Dorn- nistic" omnivore, ingesting various to the development of egg yolks berg to conclude that the gravid types of animal matter for mineral and egg shells. females engaged in lithophagy and supplementation (Leuteritz 2003). osteophagy to overcome mineral Researchers also observed red- deficiencies in their diet during the During his studies of the feeding footed tortoises ingesting sand formation of their eggs. As men- behavior of the radiated tortoise in during their foraging activities and tioned, egg yolks and egg shells are southwestern Madagascar, Thomas identified sand in scat analyses. largely composed of calcium, phos- Leuteritz (2003) recorded the Sand could aid in the digestion of phorus, and other minerals. ingestion of fish and mammal bones tough foods, and might be a source and bone fragments, snail shells, of minerals for the tortoises. [ References Cayot, L. (1987). Ecology of Giant Tortoises (Geochelone elephantopus) in the Galápagos Islands. Ph.D. dissertation, Syracuse Univer- sity, New York. p. 271. Esque, T. and Peters, E. (1994). Ingestion of bones, stones, and soil by desert tortoises. In: R. B. Bury and D. J. Germano, eds. Biology of North American Tortoises. Washington, DC: USDI National Biological Survey, Fish and Wildlife Research 13. pp. 105-111. Leuteritz, T. (2003). Observations on diet and drinking behaviour of radiated tortoises (Geochelone radiata) in Southwest Madagas- car. African Journal of Herpetology, [online] 52(2), pp.127-130. Available at: http://dx.doi. org/10.1080/21564574.2003.9635490 Moore, J. and Dornberg, A. (2014). Ingestion of Fossil Seashells, Stones and Small Mammal Bones by Gravid Gopher Tortoises (Gopherus polyphemus) in South Florida. Bulletin of the Peabody Museum of Natural History 55(1), pp.55-63. Naish, D. (2014). Turtles that eat bone, rocks and soil, and turtles that mine. [Blog] Tetrapod Zoology. Available at: https://blogs. scientificamerican.com/tetrapod-zoology/ turtles-that-eat-bone-rocks-and-soil-and- turtles-that-mine/ Nikolić, M., Savić, D., Ilić, M., Stojadinović, D., Crnobrnja-Isailović, J.: A note on scavenging behaviour of adult Hermann’s tortoise (Testudo hermanni). Biologica Nyssana, 7 (1), September 2016: 53-55. Rosenberg, M. (2018). Geophagy – Eating Dirt. [online] ThoughtCo. Available at: https://www.thoughtco.com/ geophagy-eating-dirt-1433451 Walde, A., Delaney, D., Harless, M. and Pater, L. (2009). Osteophagy by the desert tortoise (Gopherus agassizii). The Southwestern Naturalist, 52(1), pp.147-149. Wang, E., Donatti, C., Ferreira, V., Raizer, J. and Himmelstein, J. (2011). Food Habits and Notes on the Biology of Chelonoidis carbonaria (Spix 1824) (Testudinidae, Chelonia) in the Southern Pantanal, Brazil. South American Journal of Herpetology, 6(1), pp.11‑19. Yost, R., Martinez, R., Gibbs, J. and Blake, S. (n.d.). Potential role of soil calcium and phosphorus on Galápagos tortoise growth.

Special thanks to Karen Berry of the CTTC’s Valley chapter for her invaluable assistance during the preparation this article.

Originally published in the Tortuga Gazette 55(2), March/ April 2019.