|Chicken turtle lithograph of 1842|
|Chicken turtle basking|
D. r. chrysea Schwartz, 1956
The chicken turtle (Deirochelys reticularia) is an uncommon freshwater turtle found in the southeastern United States. It is in the monotypic genus Deirochelys.
The word "chicken" in chicken turtle is apparently a reference to the taste of their meat, which used to be both common and popular in southern markets.
The chicken turtle (D. reticularia) is the only extant species in the genus Deirochelys. Its parent family is Emydidae, the freshwater and marsh turtles, which are found on every continent except Australia. The name of the genus is derived from the Ancient Greek words for "neck" (deirḗ) and "tortoise" (khélūs), a reference to the species' particularly long neck. The species name comes from the Latin for "net-like" or "reticulated" (reticulatus), probably alluding to the turtle's patterned carapace (top shell).
The species was first described in 1801 independently by two French zoologists: as Testudo reticularia by Pierre André Latreille, and as Testudo reticulata by François Marie Daudin. Both descriptions were based on drawings and a specimen collected by Louis Augustin Guillaume Bosc in the vicinity of Charleston, South Carolina some years previously. Subsequent studies placed the chicken turtle into various related genera (Emys, Clemmys and Terrapene) before Louis Agassiz assigned it to the current monotypic genus in 1857. He distinguished D. reticularia from other North American members of the family Emydidae by the length of its neck and the articulation of the neck vertebrae. In a comparison of Latreille and Daudin's original descriptions, Francis Harper determined that Latreille's had been published first, hence the currently accepted specific name.
There are three distinct subspecies of chicken turtle, as described by Albert Schwartz in 1956 from a study of 325 specimens:
Schwartz considered that D. r. reticularia is probably most reminiscent of the ancestors of Deirochelys, and that the other two subspecies most likely developed from it. The western chicken turtle is the most divergent of the three subspecies, suggesting a longer period of separation, possibly after populations were cut off from one another during a period of glaciation. Similarly, D. r. chrysea developed from a later population separation, a common phenomenon on the geographically diverse Florida peninsula. It is thought that the Mississippi River prevents intergradation (the presence of populations sharing characteristics of two subspecies) between D. r. miaria and D. r. reticularia since the chicken turtle does not generally inhabit rivers or moving water. Intergrades of the eastern and Florida chicken turtles are known, however, with several specimens having been collected in north-central Florida.
It is posited that ancestors of the chicken turtle and related turtles of the genus Chrysemys may have been present in North America for up to 40 million years. D. reticularia is considered to have "one of the most complete evolutionary records of any Recent turtle". Fossils have been found throughout its current range; examples dating from the Pliocene (roughly 5.33 to 2.58 million years ago) to the sub-Recent have been discovered in Florida, in addition to fossils in Pleistocene deposits in South Carolina. A fossil found in Alachua County, Florida dating from the middle Pliocene was originally thought to belong to D. reticularia, but was later identified by Jackson as an extinct ancestor, D. carri. This species was somewhat larger than its modern relative and its shell roughly twice as thick. Other fossils from the Hemingfordian (20.6 to 16.3 million years ago) are considered to belong to even earlier, more primitive members of the genus.
Like other members of the family Emydidae, the chicken turtle's karyotype consists of 50 chromosomes; 26 macrochromosomes and 24 microchromosomes. This has been used as evidence supporting the lack of close relation between the emydids and the wood turtles of the genus Rhinoclemmys, the only New World genus in the family Geoemydidae, which have 52 chromosomes. Studies of the chicken turtle's mitochondrial DNA support the theory of earlier divergence of the western subspecies from the two eastern ones. A 1996 study of various turtles' RNA supported the partition of Emydidae into two subfamilies, Emydinae and Deirochelyinae, with Deirochelys placed within the latter.
The chicken turtle resembles the painted turtle (Chrysemys picta) and some species of cooter (genus Pseudemys) in appearance, but has an unusually long neck that is close to the length of its shell. It often also has black blotches on the underside of the bridge (the part of the shell connecting the carapace and plastron), which are not present in these other species. The carapace of the chicken turtle is elongated and pear-shaped, with the rear half noticeably wider than the front. It ranges from dark green to brown in color, and features a distinctive yellowish net-like pattern across its entire upper surface. The scutes of the upper shell have a ridged or wrinkled texture and are rough to the touch. Beneath its shell, the chicken turtle has particularly slender ribs, supposedly developed to accommodate its long, muscular neck.
Descriptions of the chicken turtle disagree on the base color of its skin but it is generally reported to be darker than the carapace, varying from olive to brown to black. One of the distinguishing features of D. reticularia is a broad yellow stripe on the forelegs. The skin of the neck and head also has light stripes, although narrower, while the tail and rear legs show vertical yellow markings. The head itself is elongated with a somewhat pointed snout but no other notable features.
Compared to other turtles, the chicken turtle is small to medium in size. Adults vary in length from around 10–25 cm (4–10 in), with an average length of around 13 cm (5 in). The width of the carapace is roughly 65 percent of its length. Mature chicken turtles exhibit some degree of sexual dimorphism; the females are larger and heavier than males, although the male has a longer and thicker tail. Unlike the painted turtle, there is no difference between the sexes in terms of the length of the foreclaws.
Chicken turtle hatchlings measure approximately 28–32 mm (1.1–1.3 in) and weigh around 8–9 g (0.28–0.32 oz). The shell is much rounder than the adults', and the shell and skin are considerably brighter in color, with a greater number of light stripes. The young of the western chicken turtle hatches with the distinctive dark markings on its plastron already present.
The chicken turtle is found throughout the southeastern United States; its range extends from the Atlantic coastal plain and states such as North Carolina, South Carolina, Georgia and Florida westward through the Gulf plain towards the Mississippi River. It tends to remain in coastal areas and is largely absent from the Piedmont plateau and more mountainous regions in the north of these states. West of the river, its territory reaches as far north as Missouri and as far west as central Texas and Oklahoma. Across its range, the chicken turtle is thought to inhabit many hundreds or possibly thousands of wetland sites, although populations in any particular location are generally small.
The eastern chicken turtle is the most widespread of the three subspecies, with specimens known from eight states. The main bulk of its territory begins on the eastern banks of the Mississippi River in southeast Louisiana and extends eastward along the coastal plain of the Gulf of Mexico. Apart from the coastal region in the south of the state, it is not present in most of Mississippi, save for a small population which inhabits the drainage basin of the Tombigbee River. In Alabama, it is again commonly found throughout the coastal plain in the southern half of the state. It is also present further north in the Ridge and Valley region of the Appalachian mountain range, although less common.
Through Georgia, South Carolina and North Carolina the eastern chicken turtle is again widely found throughout the coastal regions, although specimens have been recorded further inland in North Carolina. Isolated groups are also known in the Outer Banks chain of barrier islands off North Carolina, although the turtle does not generally inhabit island habitats. It is abundant in northern Florida, especially in the Panhandle region, where it is the only subspecies present. Its range begins to overlap with the Florida chicken turtle towards the north-central part of the state, with intergrades having been identified in Taylor, Levy, Gilchrist and Clay counties.
The eastern chicken turtle is also present in Virginia, although it is very rare there. A small colony was known to inhabit First Landing State Park in Virginia, but several studies have only managed to locate one adult female and it is thought this population may be extirpated. Around 40 mi (64 km) to the west, a small group of around 30 adults is present in Isle of Wight County. Neither of these locations is contiguous with the rest of the turtle's range; it is unclear whether these populations are relics of a native and formerly more widespread group, or whether they were introduced to the area.
As its name suggests, the Florida chicken turtle is native to Florida and is only found within the state. It is relatively widespread throughout the central and southern portions of the state, although it is absent from the Florida Keys.
The western chicken turtle's range is generally restricted to locations west of the Mississippi River, although specimens have been found on the river's eastern banks in northwest Mississippi state. Its range extends from the coastal plain of the Gulf of Mexico in Texas and Louisiana, northward into the south and east of Oklahoma and through Arkansas towards Missouri. It may once have been common in the swampland of Missouri's Bootheel region, but is now only found in a few small groups in the extreme southeast of the state. In Arkansas too its territory is decreasing in size; diffuse groups are now found only in the northern reaches of the Gulf coastal plain in the south of the state as well as some regions of the Arkansas River Valley. The western chicken turtle is still reasonably uncommon in Texas but its population there is secure. It inhabits the drainage basins of several rivers in the eastern half of the state, such as the Sabine and the Neches.
Chicken turtles are semiaquatic, equally comfortable in wetland habitats and on land. All three subspecies have similar preferences; they like quiet, still or slow-moving bodies of water such as shallow ponds, oxbow lakes, drainage ditches, borrow pits, marshes, swales, cypress swamps, and Carolina bays. Generally, the chicken turtle prefers water with a maximum depth of around 70 cm (2.3 ft), but it is known to inhabit ponds up to 2 m (6.6 ft) deep. It rarely inhabits moving water such as streams or rivers, but may sometimes colonize quieter rivulets or pools in the riparian zone. Furthermore, it strongly favors fresh water, avoiding brackish water wherever possible.
The chicken turtle thrives in bodies of water with dense aquatic vegetation and a soft, muddy substrate. Often these are ephemeral or temporary wetlands which readily dry out during the summer or in periods of drought. Such habitats tend to be free both of fish, which would provide competition for food, and potential predators such as alligators. When drying occurs, chicken turtles will migrate to the land and burrow into the soil or hide under foliage to avoid dry weather. Although they are well adapted to living terrestrially, they rarely abandon their original habitat even during extended dry spells, and will relocate to the water once it returns.
Chicken turtles are regularly encountered on land, migrating between aquatic habitats or seeking areas to burrow into the soil and escape dry conditions. Males generally travel around farther than females. They are social, spending much of their time basking on logs and rocks and swim in small groups. Chicken turtles hibernate in the soft mud, but only in the northern part of their range, and vegetation of bodies of water. They are known to be timid but if caught they generally will bite very easily.
The mating season of the chicken turtle can be estimated by the times of year in which male testicular volume is greatest, indicating maximum sperm production. This time period varies depending on location; in Florida, the male testes reach their largest size during the hottest months of summer. Meanwhile, in South Carolina and the slightly cooler climate of Missouri, this occurs in the late spring and early summer months (roughly May through July). In Texas, courtship may take place in the early spring (February to April) or fall (September to November). The chicken turtle's mating ritual is initiated by the male, who will swim at an angle towards the female turtle until he is facing her head-on. He will then attract the female's attention by making short, rapid swimming motions, gazing at her and vibrating his outstretched foreclaws against her face and neck. Only if the female is receptive does copulation occur. There is no evidence of forced insemination as sometimes seen in other related turtles. After copulation, the female turtle can retain eggs for several months until the nesting season begins or a suitable nesting site is found. Chicken turtle mating takes place in shallow waters, and reproduction can be disrupted by prolonged periods of dry weather.
Nesting season depends on latitude. For example, in Florida nesting takes place between mid-September and early March. Females lay between five and twelve eggs. A period of up to six months may pass between the mating event and the female laying her eggs. Females excavate cylindrical nest on land in a variety of soil types, from sandy to heavy soils. Chicken turtle embryos go through a period of diapause in the late gastrula stage. They must experience a period of cool temperatures before development proceeds. Eggs hatch in 152 days at 29 Celsius, some eggs may overwinter in the nest before hatching. Incubation temperature influences the sex of the embryos, with a 25 degrees Celsius incubation temperature resulting in all males. Warmer temperatures result in an increase in female embryos, with only 11 percent becoming males at incubation temperatures of 30 degrees Celsius.
Wild chicken turtles have been recaptured up to 15 years after their first capture. Some reached the known maximum ages of 20 to 24 years.
The chicken turtle is described in older guidebooks as omnivorous. More recent works present it as predominantly carnivorous, with seemingly incidental ingestion of plant matter. In the wild they have been observed to prey on crayfish, invertebrates, tadpoles, vegetation and carrion, including dead fish and other animals. Carr described having seen a chicken turtle eating Nuphar (bonnet-lily) buds, while captive adults have been observed feeding on gopher frog tadpoles, lettuce, and canned fish. A study undertaken during the summer months in South Carolina examined the chicken turtle's diet through its fecal material; dragonfly nymphs were the most commonly observed food, along with snails, spiders and insects such as backswimmers and water bugs. Only six out of forty-three specimens had ingested plant material. Like many species in the family Emydidae, chicken turtles are almost completely carnivorous during the first year of their lives. However, they are unusual in preferring a carnivorous diet into adulthood. It has been suggested that this explains the smaller local populations of D. reticularia compared to other related turtles due to competition with fish for food, especially insects.
The chicken turtle is an aquatic hunter; it waits in the water and strikes its long neck out quickly with its mouth open to catch live food. The length of the neck allows it to capture fast-moving prey such as fish and spiders, which would otherwise be able to escape. Like Blanding's turtle (Emydoidea blandingii), the chicken turtle uses a sucking motion when feeding; any water taken in during the process is expelled before the food is swallowed whole. The Florida chicken turtle is known to feed passively, swimming along with its long neck extended and foraging in clumps of vegetation.
Information regarding predation of the chicken turtle is scarce, but it is presumed that common predators such as raccoons, skunks and snakes feed on eggs and juvenile turtles. Fire ants are also known to attack hatchlings of D. reticularia and other turtles. Hibbitts and Hibbitts suggest humans and alligators to be the main predators of the western subspecies. Snapping turtles are also listed as a possible predator.
The meat of the chicken turtle is considered palatable and was once widely sold at markets throughout the southern United States for use in turtle soup; it is thought that the vernacular name is a reference to the flavor of its meat. It is still sometimes eaten today in rural areas, although this is uncommon. Consumption by humans is no longer considered to be a significant threat to the chicken turtle.
The chicken turtle population as a whole is currently considered secure and is thought to consist of at least 100,000 adults. Local populations are often small but stable, however it is designated by NatureServe as S1 (critically imperiled) in Virginia and Missouri and S2 (imperiled) in Arkansas, Louisiana, North Carolina and Oklahoma. The chicken turtle does not appear on the IUCN's Red List of Threatened Species, although the Tortoise and Freshwater Turtle Specialist Group's own provisional list considers it Near Threatened. At the state level, the chicken turtle is protected by various local laws. In Virginia, where only around 30 adults are thought to remain, it has been listed as "vulnerable" since 1987. It is also considered at risk by the Alabama Natural Heritage Program; local regulations state that only two turtles may be kept and these must be for personal use (e.g. as pets). Along with other native reptiles, removal of chicken turtles from their natural habitat is regulated in several states throughout its range including Texas, Georgia and North Carolina. The chicken turtle is subject to a ban on commercial taking in Arkansas, where it is "extremely rare". In Missouri, where until 1995 no sightings had been recorded for at least 33 years,[nb 1] it is listed as an endangered species, making hunting illegal.
Habitat loss appears to be the most significant threat to the stability of chicken turtle populations. Human activity is one cause of this; the turtle's preferred wetland habitats are often converted for agriculture, such as rice farming, or building developments. In Missouri and Arkansas in particular, the destruction of swampland and bottomland hardwood forests is a direct threat to the chicken turtle. Man-made obstacles, such as fences and road barriers can also lead to populations becoming isolated. Since it prefers to live in small, shallow bodies of water which can easily dry out during the hotter months, the chicken turtle is also susceptible to the loss of upland habitats surrounding wetlands to which it migrates during periods of drought. This migration leads to turtles, especially females in search of suitable nesting sites, coming into contact with roads, where they are killed by traffic. Fire is a further threat; wildfires are becoming increasingly common and while controlled burns can help to protect wetland habitats by decreasing the risk of wildfire, chicken turtles which are overwintering on land or which have been forced onto the land during drier months can be caught up in them.
Several locations inhabited by chicken turtles are already under protection, having been designated as wildlife reserves or conservation areas. However, further preservation of wetlands, especially temporary ones, would be beneficial in ensuring the continued stability of the population. In particular, the protections currently in place rarely include the surrounding areas of land which the chicken turtle inhabits for much of the year.
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