David T. Kirkpatrick, Ph.D
Mud turtles of the genus Kinosternon frequently are considered, by those people that even know they exist, to be small, drab and undistinguished turtles. In the wild, many people live near populations of mud turtles without ever noticing their presence. In addition to being overlooked in the wild, mud turtles are often ignored by herpetoculturists. Many of the species of mud turtle are only represented by a few animals in collections at only one or two institutions, while other turtle species are kept by many different zoos. Given their small size and uncomplicated requirements, this oversight is hard to understand. For a number of reasons, mud turtles are very good candidates for captive maintenance and breeding projects. This article will discuss the natural history and captive maintenance of one type of mud turtle: Kinosternon baurii, the Striped Mud Turtle.
The Natural History of Striped Mud Turtles
Of the mud turtles, one of the most easily recognized is K. baurii, the Striped Mud Turtle. This chelonian is small, even for a mud turtle, reaching a total length of not quite 13 cm. Most individuals have three light stripes running the length of the carapace and a facial stripe between the eye and nose. The skin is usually dark, but can be mottled. The carapace is often a dark brown in color, although lighter shades are possible. The plastron is usually yellow. The carapace is oval when viewed from above, and lacks keels. In fact, the central scutes are occasionally depressed slightly. As with all mud turtles, the plastron has two strong hinges. Male turtles are slightly smaller than females and have a much longer and thicker tail that sports a terminal nail.
Striped Mud Turtles range from the Florida Keys up the Atlantic coast into Virginia. At one point the southern Florida Striped Mud turtles were grouped into a separate subspecies, K. baurii palmarum. However, the distinguishing characteristic, a transparency in the carapacial scutes, was shown to occur throughout the turtle's range, and the subspecies designations were dropped. In the past the northern populations were often confused with Common Mud Turtles (Kinosternon subrubrum). Researchers determined a set of characteristics to distinguish the two species (Lamb and Lovich, 1990), proving the validity of the northern populations of K. baurii.
Further detailed scientific study of the taxonomy of Striped Mud Turtles may help to resolve an ongoing debate among turtle researchers concerning the relationship between the mud and musk turtles. Some taxonomists believe that the two groups should be combined into one genus, Kinosternon, while others favor maintaining Kinosternon and Sternotherus independently. In 1986 scientists published a study comparing proteins in 18 types of mud turtles (Seidel et al, 1986). While the data agree with other studies, the researchers argued that the Striped Mud Turtle and the Common Mud Turtle were actually more similar to musk turtles than they were to other mud turtles, especially the South and Central American species. Based on this relationship, they relegated Sternotherus to subgeneric status (i.e. Sternotherus odoratus becomes Kinosternon odoratum, etc.). A few years later, John Iverson published a study on differences in the shell, pelvis and skin of mud and musk turtles (Iverson, 1991). As he could find no character that clearly seperated mud and musk turtles, he followed the newer grouping. Some authors also adopted the revised Kinosternon genus; others have remained unconvinced. In Ernst and Barbour's 1989 Turtles of the World, they included Sternotherus in Kinosternon. However, with the publication of the 1994 volume Turtles of the United States and Canada, Ernst, Lovich and Barbour question the split, wondering "why not relegate K. baurii and K. subrubrum to the genus Sternotherus rather than the four Sternotherus species to Kinosternon?" (pg 138). Obviously, the jury is still out on the status of Sternotherus and Kinosternon!
Striped Mud Turtle habitat varies within the turtle's range, but in general they prefer slow-moving or still bodies of water. Preferred locations often have soft-bodied beds, either consisting of sand or mud, and support a large amount of aquatic vegetation. As Striped Mud Turtles are omnivorous, this vegetation can serve as food or hide the insects that are also part of the turtle's diet. Like many mud turtles, K. baurii will nose around in the soft muck, probing for food.
While mud turtles frequently are often considered to be largely aquatic in habits, rarely found out of the water, under certain circumstances they will spend time on land. The Striped Mud Turtle will estivate during the hottest part of the summer underground, especially if the local ponds dry up. When on land, they will often favor small shallow burrows dug into the soil. Female mud turtles will also be found on land when they are searching for a suitable area for nesting.
The Captive Care of Striped Mud Turtles
Mud turtles can be maintained readily in captivity if care is taken to address their environmental needs. Depending on the local conditions, outdoor maintenance may be possible, especially within their native range. Animals kept outside will require a water area and a land area. These areas should be enclosed to prevent turtles from escaping or predators from entering. As mud turtles occasionally are preyed upon by large birds or climbing animals such as raccoons, the whole enclosure should be covered to prevent loss of turtles. Outdoor maintenance has the advantage of giving the turtle a more natural environment, which may lead to greater success in maintenance and breeding these turtles. However, the keeper cannot observe the turtle as closely as turtles kept indoors, and may miss early signs of illness.
Most turtle owners opt to keep their animals indoors. Given the small size of K. baurii commonly available aquariums can be used to create suitable environments. A pair of turtles will do well in a 20 or 30 gallon aquarium, while larger groups require more spacious accomodations. An area of sandy dirt of sufficient depth to permit the turtle to lay its eggs is a necessity if breeding is planned or might occur. Land areas can be constructed in aquariums by walling off a section of the tank using appropriately sized pieces of glass or plastic attached with silicone aquarium sealant. A good use of space is to make a suspended 'island' in the tank with three pieces of plastic: two positioned vertically and one running horizontally, parallel to the tank bottom but suspended a few inches above it. Conveniently placed rocks, wooden cork floats, or ramps constructed of plastic can be positioned to allow access to the area. Using suspended islands allows underwater hiding areas to be created. Many mud turtles take advantage of naturally occurring underwater shelters created by rocks or tree roots, and will use artificially created caves or tunnels readily.
Depending on the desires of the turtle-keeper, tank decorations can range from minimal to elaborate, as long as the needs of the turtle are considered. A setup that duplicates the native habitat as closely as possible can be very attractive, and allow the keeper to observe normal behaviours of the turtles. At the other extreme, a minimalistic setup is very easy to maintain. Sand, gravel, a layer of silt, or bare glass can be used for bottom substrates for mud turtles. Piles of rocks, wooden logs or cork-bark floats can be provided; broken clay pots often make suitable underwater caves. Keep in mind that tank decorations increase the maintenance required to keep the water clean, as they provide inaccessible areas where dirt will accumulate. Decorations must be arranged carefully; if a turtle becomes trapped underwater it can drown. Finally, mud turtles are active foragers and will dig up aquarium decorations while searching for food. If plants are provided they may need to be replaced if the turtles eat them or rip them up.
Filters and heaters are essential equipment for Striped Mud turtle enclosures. Filtration of the water is a necessity if you don't want to do daily water changes. In general, the larger the filtering unit, the better in terms of ease of maintenance and water cleanliness. Canister filters, either submerged or placed outside the tank, are probably the best choice. Undergravel filters may be overloaded by waste material, especially in smaller aquariums. Submersible heaters that can be set to maintain a desired temperature work well in mud turtle enclosures. Care should taken to ensure that turtles can't break the heater, but water should still be able to flow around the heater to prevent localized hot spots that may be dangerous.
A basking area where the turtles can climb out of the water and dry out completely should be provided, although it may not be used frequently. The basking area should be lighted with an incandescent light, heating it more than the surrounding area. Animals kept indoors will require normal day and night lengths. Striped Mud Turtles are often active in the early morning or late evening. Lights should be provided on a timer that is keyed to either the outside day length (especially if the turtle is kept in a room with windows) or to the day length in their native environment.
Striped Mud Turtles are opportunistic omnivores or carnivores. They will eat many different types of food, depending on what is available to them. In captivity Striped Mud Turtles will eat many of the items that they eat in their natural habitats. Various insects, earthworms, and fish are all readily eaten, for example. Commercial turtle foods and trout chows can be provided, although it may take some animals a while to adapt to these foods. Items should be varied to provide a complete diet and to prevent the turtle from becoming addicted to one type of food. Captive turtles in the author's collection are fond of calcium blocks made of plaster of paris with added vitamin and calcium powder. In addition to the benefits from the calcium and vitamins, the blocks also help keep a turtle's beak worn down.
Striped Mud Turtles can live quite a long time. Ages of almost two decades have been recorded, although one turtle approximately ten years old when captured lived for almost 50 years in captivity. The record-holder for the whole group appears to be a musk turtle that lived for over 54 years at the Philadelphia Zoo (Slavens, 1995).
Captive Breeding of Striped Mud Turtles
Using the care regimen and habitats described above, we have successfully bred Striped Mud turtles in captivity. Our colony of K. baurii began by accident - we rescued some unidentified eggs from a pet store aquarium containing a number of different species of mud turtles. The eggs hatched and within a year or so the distinctive markings of K. baurii became apparent. Initially we did not plan on working with this species, but after we were given an adult female in addition to our juveniles we decided to attempt to breed them. Pairs were maintained together, in 20 gallon "long" or larger aquariums. No attempts were made to hibernate the turtles. Lights for the enclosures were on a timer set to simulate the natural day length, while temperature as a whole was varied similarly.
Soon after pairs were set up, mating was observed. In general, mud turtles do not have an elaborate courtship procedure. Usually there is a phase where the male follows the female, sniffing at her vent and the bridge between the carapace and plastron. These actions can be accompanied by a head-to-head confrontation or nudging by the male. The female will, on occasion, bite at the male and he may bite back. If the female retreats, the male will follow, repeating the sniffing and nudging until she stands still. He then mounts her from the side or rear, using all four feet to grasp the shell. At this point male mud turtles will often lean forward and bite at the female's head. When actual copulation takes place, the male may move backward or up at an angle to the female's carapace. This position can be maintained for quite a while. The female is capable of dragging the male to the surface to breathe during the course of the mating procedure. Female Striped Mud Turtles can also store sperm for over a year. Female K. baurii will deposit up to seven eggs. Chelonians in our collection have laid clutches with one to three eggs. Mating in our groups was fairly constant throughout the year, as was egg deposition, which occurred approximately every six to eight weeks.
The sex of hatchling mud turtles is dependent on the temperature at which the eggs were incubated (known as temperature-dependent sex determination and commonly abbreviated as TSD). For mud turtles, eggs incubated at an intermediate temperature range give predominantly male turtles, while females are produced at temperatures above or below this temperature interval (Ewert et al., 1991). Sphagnum moss or a dirt/vermiculite mixture hold water well and are often used to incubate mud turtle eggs. Incubation can take from two and a half to five months. Mud turtle eggs can undergo a diapause period, especially those laid in the fall. A period of chill temperatures followed by a warming may be required to end the diapause and allow development to begin again (Ewert and Wilson, 1996), which can make artificial incubation more difficult. We have not seen evidence of diapause in our population, however. A while before hatching, a longitudinal crack often develops around the egg. The baby will use its eggtooth and forefeet to punch a small hole at one end. Hatchlings in our collection have taken up to 96 hours to emerge after opening this hole, however. Hatchling K. baurii can be as small as 16.5 mm. The carapace of hatchlings is very dark and cylindrical in shape immediately after hatching. The carapace flattens out during the first few days following hatching; the sharp sloping sides of the carapace of adult turtles take a few years to develop. The plastron of the hatchling is more colorful than the carapace - it is yellow with black markings. The facial markings of Kinosternon baurii become apparent early in the turtle's life.
Hatchlings in our colony initially are kept individually or in small groups of similarly-sized animals in plastic tubs. The only decoration is a rock for exiting the water and basking if desired. Turtles are fed in their tubs daily for the first three months, until they have reached a size where handling is not quite so unnerving a proposition. Feeding times are reduced to every other day, and they are fed individually in separate containers to monitor each turtle's food intake. After about six months, juveniles are transferred to aquariums. No filtration system is added until they are over an inch in length. If one turtle begins to outstrip his cagemates in size, or becomes aggressive, separate quarters are provided.
In the wild, growth rates of hatchlings and juveniles depend on local conditions, including the abundance of food, the length of time available for feeding, and other variables. Breeding size may not be reached for many years for some individuals, especially those found in marginal habitats. In captivity, temperature and amount of food seem to be the determining factors in growth rates. While breeding size can be reached in two to two and a half years in captivity, mud turtles in their natural environment often take five or six years to become mature. Hatchlings and juveniles in our colony are fed amounts intended to mimic this growth rate, as we feel that overly rapid growth may have long-term health consequences. Our initial group of hatchlings reached maturity in four years.
Mud turtles with their small size, drab colorations, and cryptic habits are often overlooked, both in the wild and in captivity. However, Kinosternon turtles are intriguing chelonians with which to work, both in their natural habitat and in captivity. Their small size, moderate needs and interesting habits make them better suited for indoor maintenance than many of the larger sliders, cooters and painted turtles, and deserve more attention than they receive. Although this article has focussed primarily on the Striped Mud Turtle, K. baurii, the techniques used here are applicable to many of the species of Kinosternon.
References and Further Reading
Ernst, CH; Barbour, RW: Turtles of the United States. University Press of Kentucky, Lexington, KY, 1972, 347pp.
Ernst, CH; Barbour, RW: Turtles of the World. Smithsonian Institution Press, Washington D.C., 1989, 313pp.
Ernst, CH; et al.: Turtles of the United States and Canada. Smithsonian Institution Press, Washington, D.C., 1994, 578pp.
Ewert, MA; Nelson, CE: Sex Determination in Turtles: Diverse Patterns and Some Possible Adaptive Values. Copeia, 1991; 1991(1): 50-69.
Ewert, MA; Wilson, DS: Seasonal Variation of Embryonic Diapause in the Striped Mud Turtle (Kinosternon baurii) and General Considerations for Conservation Planning. Chelonian Conservation and Biology, 1996; 2(1): 43-54.
Iverson, JB: Phylogenetic Hypotheses for the Evolution of Modern Kinosternine Turtles. Herpetological Monographs, 1991; 5: 1-27.
Lamb, T; Lovich, J: Morphometric Validation of the Striped Mud Turtle (Kinosternon baurii) in the Carolinas and Virgina. Copeia, 1990; 1990(3): 613-618.
Pritchard, PCH: Encyclopedia of Turtles. TFH Publications, Inc., Neptune, N.J., 1979, 895pp.
Seidel, ME; et al.: Phylogenetic Relationships among Musk Turtles (Genus Sternotherus) and Genic Variation in Sternotherus odoratus. Herpetologica, 1981; 37(3): 161-165.
Slavens, FL; Slavens, K: Reptiles and Amphibians in Captivity: Breeding, Longevity and Inventory (Current January 1, 1995). Slaveware, Seattle, 1995
This article copyright © 1999 by David T. Kirkpatrick. Originally published in Reptiles, April, 1999, pg 70-78.
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