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The Red-Footed Tortoise (Geochelone carbonaria), a South American Treasure

by Petra Spiess



This article appeared in the March/April 1997 issue of Reptile and Amphibian Magazine

The red-footed tortoise (Geochelone carbonaria) has been an enduring favorite in the herpetocultural trade for years. This medium-sized South American tortoise is hardy, beautiful, and displays a variety of interesting behaviors. Although there are quite a number of red-foot breeders in the United States (most notably in Florida), red-foots are still imported for the pet trade. Consequently, the price of red-footed tortoises does not reflect their actual value as a unique and important species in South American ecology. Red-foots are protected under Appendix II of The Convention on International Trade in Endangered Species (CITES), meaning that this species may not be exported from its home country without a permit. Appendix II animals are not classified as threatened with extinction, but are considered sensitive to this danger if international trade is left unregulated (Levell, 1995). Although protection under CITES has some positive effects on the survival of this species, CITES regulations cannot protect the red-footed tortoise where it is most in danger, within the boundaries of its home countries.



Threats to Survival



The red-footed tortoise is found throughout extreme southern Central America, and central and northern South America including the countries of Panama, Colombia, Venezuela, Guyana, Surinam, French Guyana, Brazil, Bolivia, Paraguay, and Argentina. Red-foots are also found on several Caribbean islands, but it is thought that this species was introduced in the seventeenth century as a convenient food source (Prichard and Trebbau, 1984). In every country in its range, the biggest threat to the survival of red-footed tortoises is overhunting by man (Walker, 1989). Red-footed tortoises are hunted extensively in their countries of origin for food. Interestingly enough, tortoises are considered "fish" by the Catholic church and during holy week, red-foots are consumed in huge numbers. Red-foots are collected in large numbers and shipped to many different South American cities to be sold as a delicacy. The fact that red-foots can tolerate long periods of time without food and water, an otherwise evolutionary advantage, makes this species both easy and profitable to transport. Another treat facing red-foot populations is the omnipresent habitat loss and disturbance.



Although it has been observed that red-footed tortoises can live on land that has been converted to agriculture (Legler, 1963), their densities are much lower than they are in natural, unaltered habitat. Tortoises living on agricultural lands are much easier to locate, so higher hunting rates may account for this difference. Exportation for the pet trade also has a negative effect on red-footed tortoises, although it is much less of a threat to their survival than either hunting or habitat loss. The natural history of the red-footed tortoise provides insight into two areas, the susceptibility of this species to overhunting and habitat loss, and captive husbandry and reproduction.



Natural History



Red-footed tortoises are a medium sized species. Red-foot males are larger than females in carapace length and weight, but are not wider or taller (Moskovits, 1988). As with other tortoise species, male red-foots have a concave plastron. As red-foots mature, both sexes develop a unique mid-body constriction (some have referred to it as a "waist") that, from a top view, gives the tortoises a decidedly hourglass appearance. This "hourglass" figure is much more developed in males than in females. Mature males also have longer and wider tails than females.



Red-footed tortoises undergo an ontogenetic color change. Juveniles have a carapace with a pale yellow or horn ground color, with increasing dark brown or black patches as the animal matures. Adults have a carapace with a dark brown or blackish brown ground color with pale yellow aureole in the center of each lateral and center scute. Enlarged scales on the legs and tail vary from yellow to dark cherry red, the brightest colors are generally seen on adult males. Enlarged scales on the head range from pale yellow to bright red (Legler, 1963). There is considerable variation in color over the range of the red-foot tortoise, so no one description will accurately describe every specimen.



Although red-foots are commonly found in relatively dry grassland and forest areas, this species is also found in humid forest habitat. There is some disagreement as to which habitat is the preferred type. Walker (1989) states that red-foots prefer grasslands and dry forest areas, and that rain-forest habitat is most likely marginal. Other authors however, state or suggest that humid forest is the preferred habitat (Legler, 1963) (Moskovits, 1988). In the wild, red-foots are reported as being primarily herbivorous, but also consuming a small amount of animal matter such as carrion (Moskovits, 1985). Red-foots are most active after the rainy season when mating occurs. Male red-foot tortoises engage in combat, with rival males will attempting to overturn one another. It is interesting to note than in almost every tortoise species where male combat occurs, the males are always larger than the females. This is in comparison to aquatic species, where the males are usually smaller than the females and do not engage in male to male combat. It is thought that species with male combat evolved larger males because larger males have a better chance of winning a bout and mating with a female, thus passing on their larger size to their offspring. Species with smaller males evolved because smaller males are more mobile and can mate with a large number of females, thus passing on their genes (Berry and Shine, 1980). In natural habitat, mating takes place after the rainy season, from July to September, and clutches vary from 5-15 eggs (Medem, 1962). Red-footed tortoises, and many other tortoise species, are slow to mature and do not reach sexual maturity for several years. This, coupled with a relatively low clutch size, makes the red-footed tortoise susceptible to overhunting. With overhunting, more sexually mature animals are removed from the population than can be replaced by maturing juveniles, consequently, the overall population begins to decline. Although the red-footed tortoise is not currently classified as endangered, if the hunting rate and habitat loss continue at their current levels, it will most likely be so in the future. Conservation efforts include the establishment and protection of wildlife reserves and national parks, where red-footed tortoises and other animals are protected from hunting (Walker, 1989).



Captive Care



Housing



Even though red-footed tortoise are medium-sized, they still need a large area or enclosure to roam in. Three square yards (2.7 square meters) per tortoise is recommended (Rundquist, 1994). Red-foots seem to do best when housed outside in areas where the relative humidity is moderate to high, and nighttime temperatures do not drop below 50 degrees F (10 degrees C). If housed outside, the tortoises must be provided with shaded shelter areas. Red-foots prefer to spend the majority of their time underneath bushes or tall grass (make sure the vegetation is non-toxic). The tortoises must be provided with a shallow pool of clean water they can soak in and drink from, as redfooted tortoises are not aquatic, they do not require a deep pool of water for captive purposes.



If a breeding group of five animals is housed indoors, their enclosure must be at least 15 square yards (13.5 square meters). Indoor enclosures can be constructed from a variety of materials, but the bottom material should always be water resistant. Concrete floors are not recommended because they tend to be very cold and have been reported to cause prolaspe of the penis in male red-foots (Rendquist, 1994). The sides of the enclosure should be at least three feet (.9 meters) tall or taller to prevent the tortoises from crawling out. For substrate, a mixture of peat moss and playground sand works well. The tortoises should be provided with hiding and humidity areas. An easy way to accomplish this is to bury a tall plastic trash container horizontally in the substrate so that a tortoise could fit inside. Moisten the substrate inside the hiding area to increase the humidity. The cool end of the enclosure should be 70-75 degrees F (21 to 24 degrees C) and the heated end should be 85-88 degrees F (29 to 31 degrees C). Make sure to provide several heated areas so the tortoises do not have to compete for basking sites. The nighttime temperature can drop to 55-60 degrees F (13 to 16 degrees C), but have some supplemental heating available at 80 degrees F ( 27 degrees C). Full Spectrum lighting that emits UVB should be suspended over the enclosure to promote the synthesis of vitamin D3 ,which is necessary for calcium absorbtion. It is best however, to allow the tortoises access to unfiltered, natural sunlight, weather permitting. Many breeders house their tortoises outside during the spring and summer, and bring the animals indoors during inclement weather and the fall and winter months. Red-footed tortoises do not hibernate and cannot tolerate extended periods of cold temperatures. A large, shallow water pan should be available at all times. The red-footed tortoise () has been an enduring favorite in the herpetocultural trade for years. This medium-sized South American tortoise is hardy, beautiful, and displays a variety of interesting behaviors. Although there are quite a number of red-foot breeders in the United States (most notably in Florida), red-foots are still imported for the pet trade. Consequently, the price of red-footed tortoises does not reflect their actual value as a unique and important species in South American ecology. Red-foots are protected under Appendix II of The Convention on International Trade in Endangered Species (CITES), meaning that this species may not be exported from its home country without a permit. Appendix II animals are not classified as threatened with extinction, but are considered sensitive to this danger if international trade is left unregulated (Levell, 1995). Although protection under CITES has some positive effects on the survival of this species, CITES regulations cannot protect the red-footed tortoise where it is most in danger, within the boundaries of its home countries.The red-footed tortoise is found throughout extreme southern Central America, and central and northern South America including the countries of Panama, Colombia, Venezuela, Guyana, Surinam, French Guyana, Brazil, Bolivia, Paraguay, and Argentina. Red-foots are also found on several Caribbean islands, but it is thought that this species was introduced in the seventeenth century as a convenient food source (Prichard and Trebbau, 1984). In every country in its range, the biggest threat to the survival of red-footed tortoises is overhunting by man (Walker, 1989). Red-footed tortoises are hunted extensively in their countries of origin for food. Interestingly enough, tortoises are considered "fish" by the Catholic church and during holy week, red-foots are consumed in huge numbers. Red-foots are collected in large numbers and shipped to many different South American cities to be sold as a delicacy. The fact that red-foots can tolerate long periods of time without food and water, an otherwise evolutionary advantage, makes this species both easy and profitable to transport. Another treat facing red-foot populations is the omnipresent habitat loss and disturbance.Although it has been observed that red-footed tortoises can live on land that has been converted to agriculture (Legler, 1963), their densities are much lower than they are in natural, unaltered habitat. Tortoises living on agricultural lands are much easier to locate, so higher hunting rates may account for this difference. Exportation for the pet trade also has a negative effect on red-footed tortoises, although it is much less of a threat to their survival than either hunting or habitat loss. The natural history of the red-footed tortoise provides insight into two areas, the susceptibility of this species to overhunting and habitat loss, and captive husbandry and reproduction.Red-footed tortoises are a medium sized species. Red-foot males are larger than females in carapace length and weight, but are not wider or taller (Moskovits, 1988). As with other tortoise species, male red-foots have a concave plastron. As red-foots mature, both sexes develop a unique mid-body constriction (some have referred to it as a "waist") that, from a top view, gives the tortoises a decidedly hourglass appearance. This "hourglass" figure is much more developed in males than in females. Mature males also have longer and wider tails than females.Red-footed tortoises undergo an ontogenetic color change. Juveniles have a carapace with a pale yellow or horn ground color, with increasing dark brown or black patches as the animal matures. Adults have a carapace with a dark brown or blackish brown ground color with pale yellow aureole in the center of each lateral and center scute. Enlarged scales on the legs and tail vary from yellow to dark cherry red, the brightest colors are generally seen on adult males. Enlarged scales on the head range from pale yellow to bright red (Legler, 1963). There is considerable variation in color over the range of the red-foot tortoise, so no one description will accurately describe every specimen.Although red-foots are commonly found in relatively dry grassland and forest areas, this species is also found in humid forest habitat. There is some disagreement as to which habitat is the preferred type. Walker (1989) states that red-foots prefer grasslands and dry forest areas, and that rain-forest habitat is most likely marginal. Other authors however, state or suggest that humid forest is the preferred habitat (Legler, 1963) (Moskovits, 1988). In the wild, red-foots are reported as being primarily herbivorous, but also consuming a small amount of animal matter such as carrion (Moskovits, 1985). Red-foots are most active after the rainy season when mating occurs. Male red-foot tortoises engage in combat, with rival males will attempting to overturn one another. It is interesting to note than in almost every tortoise species where male combat occurs, the males are always larger than the females. This is in comparison to aquatic species, where the males are usually smaller than the females and do not engage in male to male combat. It is thought that species with male combat evolved larger males because larger males have a better chance of winning a bout and mating with a female, thus passing on their larger size to their offspring. Species with smaller males evolved because smaller males are more mobile and can mate with a large number of females, thus passing on their genes (Berry and Shine, 1980). In natural habitat, mating takes place after the rainy season, from July to September, and clutches vary from 5-15 eggs (Medem, 1962). Red-footed tortoises, and many other tortoise species, are slow to mature and do not reach sexual maturity for several years. This, coupled with a relatively low clutch size, makes the red-footed tortoise susceptible to overhunting. With overhunting, more sexually mature animals are removed from the population than can be replaced by maturing juveniles, consequently, the overall population begins to decline. Although the red-footed tortoise is not currently classified as endangered, if the hunting rate and habitat loss continue at their current levels, it will most likely be so in the future. Conservation efforts include the establishment and protection of wildlife reserves and national parks, where red-footed tortoises and other animals are protected from hunting (Walker, 1989).Even though red-footed tortoise are medium-sized, they still need a large area or enclosure to roam in. Three square yards (2.7 square meters) per tortoise is recommended (Rundquist, 1994). Red-foots seem to do best when housed outside in areas where the relative humidity is moderate to high, and nighttime temperatures do not drop below 50 degrees F (10 degrees C). If housed outside, the tortoises must be provided with shaded shelter areas. Red-foots prefer to spend the majority of their time underneath bushes or tall grass (make sure the vegetation is non-toxic). The tortoises must be provided with a shallow pool of clean water they can soak in and drink from, as redfooted tortoises are not aquatic, they do not require a deep pool of water for captive purposes.If a breeding group of five animals is housed indoors, their enclosure must be at least 15 square yards (13.5 square meters). Indoor enclosures can be constructed from a variety of materials, but the bottom material should always be water resistant. Concrete floors are not recommended because they tend to be very cold and have been reported to cause prolaspe of the penis in male red-foots (Rendquist, 1994). The sides of the enclosure should be at least three feet (.9 meters) tall or taller to prevent the tortoises from crawling out. For substrate, a mixture of peat moss and playground sand works well. The tortoises should be provided with hiding and humidity areas. An easy way to accomplish this is to bury a tall plastic trash container horizontally in the substrate so that a tortoise could fit inside. Moisten the substrate inside the hiding area to increase the humidity. The cool end of the enclosure should be 70-75 degrees F (21 to 24 degrees C) and the heated end should be 85-88 degrees F (29 to 31 degrees C). Make sure to provide several heated areas so the tortoises do not have to compete for basking sites. The nighttime temperature can drop to 55-60 degrees F (13 to 16 degrees C), but have some supplemental heating available at 80 degrees F ( 27 degrees C). Full Spectrum lighting that emits UVB should be suspended over the enclosure to promote the synthesis of vitamin D3 ,which is necessary for calcium absorbtion. It is best however, to allow the tortoises access to unfiltered, natural sunlight, weather permitting. Many breeders house their tortoises outside during the spring and summer, and bring the animals indoors during inclement weather and the fall and winter months. Red-footed tortoises do not hibernate and cannot tolerate extended periods of cold temperatures. A large, shallow water pan should be available at all times. Diet Red-Footed tortoises are primarily herbivorous, consuming a wide variety of grasses, fruits, flowers, and small plants. Red-foots in the wild have been reported to consume small amounts of animal material such as carrion. In captivity, red-foots should be fed a mixture of high calcium greens, fruits, vegetables, and flowers and a small amount of animal protein. Appropriate high calcium greens include: collard, mustard, and dandelion. Other greens such as endive, watercress, romaine, kale, and escarole should also be mixed in for variety. Spinach should be fed sparingly, as it contains oxalates that bind dietary calcium, making it unavailable. Good fruits and vegetables to offer include: pumpkin, winter squash, grated carrots, crook-neck squash, zucchini, papaya, mango, kiwi, melon, cantaloupe, frozen mixed vegetables (thawed), and prickly pear fruits. Feed cruciferous vegetables such as broccoli, cauliflower, and brussel sprouts in small amounts, these vegetables contain iodine binders that can cause a dietary deficiency if fed as a large part of the diet. Edible flowers include: hibiscus, nasturtium, prickly-pear flowers, and dandelions. A small amount of animal protein should be offered every other feeding, high quality canned dog food and pinky mice are acceptable. Hatchling tortoises should be fed everyday, and a pinch of high quality reptile calcium supplement should be sprinkled on their food every other day. After the first year, red-foots can be fed every other day and given calcium twice a week. Two-year old tortoises and adults should be fed twice weekly and given a pinch of calcium at each feeding. Red-Footed tortoises are primarily herbivorous, consuming a wide variety of grasses, fruits, flowers, and small plants. Red-foots in the wild have been reported to consume small amounts of animal material such as carrion. In captivity, red-foots should be fed a mixture of high calcium greens, fruits, vegetables, and flowers and a small amount of animal protein. Appropriate high calcium greens include: collard, mustard, and dandelion. Other greens such as endive, watercress, romaine, kale, and escarole should also be mixed in for variety. Spinach should be fed sparingly, as it contains oxalates that bind dietary calcium, making it unavailable. Good fruits and vegetables to offer include: pumpkin, winter squash, grated carrots, crook-neck squash, zucchini, papaya, mango, kiwi, melon, cantaloupe, frozen mixed vegetables (thawed), and prickly pear fruits. Feed cruciferous vegetables such as broccoli, cauliflower, and brussel sprouts in small amounts, these vegetables contain iodine binders that can cause a dietary deficiency if fed as a large part of the diet. Edible flowers include: hibiscus, nasturtium, prickly-pear flowers, and dandelions. A small amount of animal protein should be offered every other feeding, high quality canned dog food and pinky mice are acceptable. Hatchling tortoises should be fed everyday, and a pinch of high quality reptile calcium supplement should be sprinkled on their food every other day. After the first year, red-foots can be fed every other day and given calcium twice a week. Two-year old tortoises and adults should be fed twice weekly and given a pinch of calcium at each feeding. Breeding Red-footed tortoises are capable of producing eggs at any time during the year, although seasonal activity may be noted. One collection of tortoises kept outside in Kansas during warm weather and indoors during the colder months, laid eggs only from October to April for 7 consecutive years (Renquist, 1994). Because red-foots are capable of producing eggs at any time, it is advisable to have a nesting chamber full of damp peat moss and sand available to the females at all times. A nesting chamber can be constructed by creating a large, open topped box with a ramp so the tortoises can enter and exit at will. The chamber should have the dimensions of 4 x 4 x 2 (l x w x h in feet) (1.2 x 1.2 x .6 m) and be filled with moist nesting material to a depth of at least 20 inches (50 cm). It is important that more than one male be included in a breeding group, male to male combat is important in inducing breeding in red-foots. Red-footed tortoises are capable of producing eggs at any time during the year, although seasonal activity may be noted. One collection of tortoises kept outside in Kansas during warm weather and indoors during the colder months, laid eggs only from October to April for 7 consecutive years (Renquist, 1994). Because red-foots are capable of producing eggs at any time, it is advisable to have a nesting chamber full of damp peat moss and sand available to the females at all times. A nesting chamber can be constructed by creating a large, open topped box with a ramp so the tortoises can enter and exit at will. The chamber should have the dimensions of 4 x 4 x 2 (l x w x h in feet) (1.2 x 1.2 x .6 m) and be filled with moist nesting material to a depth of at least 20 inches (50 cm). It is important that more than one male be included in a breeding group, male to male combat is important in inducing breeding in red-foots. Male to male combat begins with a round of head bobbing from each male involved, and then proceeds to a wresting match where the males attempt to turn one another over. The succeeding male (usually the largest male) then attempts to mate with the females. The ritualistic head movements displayed by male red-foots are thought to be a method of species recognition. Other tortoise species, most notably the closely related and sometimes sympatric yellow-footed tortoise (Geochelone denticulata), have different challenging head movements. Red-footed tortoises have challenging head movements that are a series of lateral jerks, by contrast, yellow-footed tortoises utilize a long sideways sweep in their displays (Auffenberg, 1965). Male red-foots peruse walking (seeming uninterested) females until they can maneuver them into a position for mating. The unique body shape of the male red-footed tortoise facilitates the mating process by allowing him to maintain his balance during copulation while the female walks around, seemingly attempting to dislodge the male by walking under low-hanging vegetation (Moskovits, 1988). Incubation and Hatchling Care Gravid females will become restless before oviposition, and will wander around the enclosure looking for a suitable nesting site. A few days before oviposition occurs, the females will begin digging in their chosen nesting site. After the eggs are laid, the female will cover the eggs with substrate. Make sure to note where the female has been digging so that the eggs can be retrieved for artificial incubation. Clutch sizes vary from one to eight eggs, although some large clutches may reach 15 eggs. Red-foots are capable of clutching several times during the year. After the eggs have been removed, bury them halfway in a container of slightly moistened vermiculite (1:1 ratio vermiculite to water by weight) and place them in the incubator. There is some controversy among tortoise breeders as to whether or not tortoise eggs should be moved from their original orientation in the nest before artificial incubation. Some breeders are careful to mark the top of the eggs so that their orientation is not changed when they are moved to the incubator. Others see this procedure at unnecessary and do not believe disorienting the eggs in the incubator has an effect on hatch rate. According to Marchellini and Davis (1982), red-footed tortoise eggs that were rotated from their original positions had a lower hatch rate, poorer survival rates, and higher incidence of hatchling deformities. Different breeders have different results, but taking care not to rotate the eggs from their original orientation does not take much effort and may improve hatching rate and hatchling success. Do not incubate the eggs in a sealed container, sealed containers encourage CO2 buildup which can be detrimental to the developing eggs. The humidity in the incubator should be 80-100% and the incubator should be opened at least once a week, if not more, to allow fresh oxygen to reach the eggs. Red-foot eggs are temperature sex dependent, incubation temperatures above 88 degrees F (31 degrees C) will produce females, and temperatures below 82 degrees F (28 degrees C) will produce males (Renquist, 1994). High temperatures however, can cause lower hatch rates and higher rates of deformed hatchlings. The ideal incubation temperature, if mixed-sex offspring are desired, is 84 degrees F (29 degrees C). Incubation periods range from 105 to 202 days, with an average of 150 days (Paull, 1995). After pipping, the baby tortoises will often spend a few days in their shell absorbing the yolk. Often hatchling tortoises will emerge with some yolk sac still present, cleanse the yolk sac with a mild disinfectant such as betadine and keep the hatchling on moist substrate until the yolk is absorbed (Renquist, 1994). Hatchling tortoises can be housed inside in aquariums on a substrate of peat moss and sand, and have the same temperature and lighting requirements as the adults. Make sure to provide areas of high humidity and a shallow water dish at all times, hatchling red-foots are very susceptible to dehydration. Gravid females will become restless before oviposition, and will wander around the enclosure looking for a suitable nesting site. A few days before oviposition occurs, the females will begin digging in their chosen nesting site. After the eggs are laid, the female will cover the eggs with substrate. Make sure to note where the female has been digging so that the eggs can be retrieved for artificial incubation. Clutch sizes vary from one to eight eggs, although some large clutches may reach 15 eggs. Red-foots are capable of clutching several times during the year. After the eggs have been removed, bury them halfway in a container of slightly moistened vermiculite (1:1 ratio vermiculite to water by weight) and place them in the incubator. There is some controversy among tortoise breeders as to whether or not tortoise eggs should be moved from their original orientation in the nest before artificial incubation. Some breeders are careful to mark the top of the eggs so that their orientation is not changed when they are moved to the incubator. Others see this procedure at unnecessary and do not believe disorienting the eggs in the incubator has an effect on hatch rate. According to Marchellini and Davis (1982), red-footed tortoise eggs that were rotated from their original positions had a lower hatch rate, poorer survival rates, and higher incidence of hatchling deformities. Different breeders have different results, but taking care not to rotate the eggs from their original orientation does not take much effort and may improve hatching rate and hatchling success. Do not incubate the eggs in a sealed container, sealed containers encourage CO2 buildup which can be detrimental to the developing eggs. The humidity in the incubator should be 80-100% and the incubator should be opened at least once a week, if not more, to allow fresh oxygen to reach the eggs. Red-foot eggs are temperature sex dependent, incubation temperatures above 88 degrees F (31 degrees C) will produce females, and temperatures below 82 degrees F (28 degrees C) will produce males (Renquist, 1994). High temperatures however, can cause lower hatch rates and higher rates of deformed hatchlings. The ideal incubation temperature, if mixed-sex offspring are desired, is 84 degrees F (29 degrees C). Incubation periods range from 105 to 202 days, with an average of 150 days (Paull, 1995). After pipping, the baby tortoises will often spend a few days in their shell absorbing the yolk. Often hatchling tortoises will emerge with some yolk sac still present, cleanse the yolk sac with a mild disinfectant such as betadine and keep the hatchling on moist substrate until the yolk is absorbed (Renquist, 1994). Hatchling tortoises can be housed inside in aquariums on a substrate of peat moss and sand, and have the same temperature and lighting requirements as the adults. Make sure to provide areas of high humidity and a shallow water dish at all times, hatchling red-foots are very susceptible to dehydration. Red-footed tortoises are an interesting and beautiful South American native to keep and breed. Unfortunately, overhunting and habitat loss threaten to make this species endangered in the future. Establishing viable captive breeding programs for red-footed tortoises can help to reduce the exportation of this species from the wild, and can subsequently help to relieve some pressure off of wild populations. Even though this species is not endangered at present, reviewing the fate of other tortoise species in this genus should provide an impetus for the conservation of this South American treasure before it is threatened with extinction. References Auffenberg, W. 1965. "Sex and species discrimination in two sympatic South American tortoises". Copeia 1965:335-342. Berry, J. F. and R. Shine. 1980. Sexual size dimorphism and sexual selection in turtles (order Testudines). Oecologia 44:185-191 Legler, J. M. 1963. Tortoises (Geochelone carbonaria) in Panama: Distribution and variation. Am. Midl. Nat. 11:279-303 Levell, J. P. 1995. Serpents Tale Books. Excelsior, MN. Marchellini, D. L. and S. W. Davis. 1982. "Effects of Handling on Reptile Egg Hatching". Herp Review. 13(2):43-44. Medem F. 1962. La distribucion geografica y ecologia de los Crocodylia y Testudinata en el Departamento del Choco. Rev. Acad. Colomb. Ci. Exact., Fis., Nat. 11:279-303. Moskovits, D. K. 1985. The Behavior and Ecology of the Two Amazonian Tortoises, Geochelone carbonaria and G. denticulata, in Northwestern Brazial. Ph.D. Dissertation, University of Chicago, Illinois. _____________ 1988. "Sexual dimorphism and population estimates of the two Amazonian tortoises (Geochelone carbonaria and G. denticulata) in northwestern Brazil." Herpetologica. 44(2):209-217. Paull, R. C. 1995. The Eight Great Tortoises. Green Nature Books. Homestead, Fl. Prichard, P. C. and P. Trebbau. 1984. "Turtles of Venezuela". SSAR, Contrib. Herpetol. 2:1-403. Rundquist, E. M. 1994. "Breeding the red-footed tortoise in captivity". Captive Breeding. 2(3):17-22. Walker, P. 1989. "Geochelone carbonaria Red-footed Tortoise" In Conservation Biology of Tortoises ed. Swingland, I. R. and W. Michael. Kelvyn Press, Inc. Broadview Il. pp. 17-19.