Chicken turtle

There are three distinct subspecies of chicken turtle, as described by Albert Schwartz in 1956 from a study of 325 specimens:[12][16]

• The eastern chicken turtle (D. r. reticularia) is the turtle originally described by Latreille in 1801. It is the largest of the chicken turtles, with males measuring up to 16.5 cm (6.5 in) and females up to 26.0 cm (10.2 in).[17] It is distinguished from the other subspecies by the coloring of its carapace, which is olive to brown with a yellow rim.[3] The plastron (lower shell) sometimes features a spot or indistinct splotch of color.[18] Its outstretched neck is especially long, sometimes as long as the carapace itself.[19]
• The Florida chicken turtle (D. r. chrysea) has the most distinctively patterned carapace of all the chicken turtles, featuring bold, broad yellow-orange reticulation.[3] The shell is cuneiform (wedge-shaped), especially so in males and juvenile turtles,[20] and measures up to 16.5 cm (6.5 in) for males and 25.0 cm (9.8 in) for females.[21] The subspecies name chrysea is taken from the Latin for "golden one" due to the bright yellow or orange color of its plastron.[22][20]
• The western chicken turtle (D. r. miaria) is the smallest of the three subspecies; males have a maximum carapace length of 16.1 cm (6.3 in) and females 21.0 cm (8.3 in).[21] Its chin and throat lack the light stripes seen on other chicken turtles and its plastron features a dark pattern along the seams.[23] The subspecies epithet miaria derives from the Greek for "stained", referring to these markings.[24] Its carapace is oval in shape and flatter than that of the other subspecies.[25]

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.[26] 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.[26] Intergrades of the eastern and Florida chicken turtles are known, however, with several specimens having been collected in north-central Florida.[18]

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.[27] D. reticularia is considered to have "one of the most complete evolutionary records of any Recent turtle".[28] 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,[29][30] in addition to fossils in Pleistocene deposits in South Carolina.[29] 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.[31] This species was somewhat larger than its modern relative and its shell roughly twice as thick.[32] 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.[29]

Like other members of the family Emydidae,[33] the chicken turtle's karyotype consists of 50 chromosomes; 26 macrochromosomes and 24 microchromosomes.[29] 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.[34] Studies of the chicken turtle's mitochondrial DNA support the theory of earlier divergence of the western subspecies from the two eastern ones.[35] A 1996 study of various turtles' RNA supported the partition of Emydidae into two subfamilies, Emydinae and Deirochelyinae, with Deirochelys placed within the latter.[36]

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.[46] West of the river, its territory reaches as far north as Missouri and as far west as central Texas and Oklahoma.[47] 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.[2]

Cypress swamp in First Landing State Park, Virginia—it is unclear whether chicken turtles are still present here

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.[17] 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.[19]

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.[17] 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.[39] 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.[20]

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.[48] 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.[20]

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.[20]

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.[20] 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.[49] 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.[50] 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.[51]

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.[2][49][52] 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.[42] Furthermore, it strongly favors fresh water, avoiding brackish water wherever possible.[35]

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,[43] and potential predators such as alligators.[53] 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.[54]

Dragonfly nymphs are a favourite food of the chicken turtle

The chicken turtle is described in older guidebooks as omnivorous.[45][56] More recent works present it as predominantly carnivorous,[39][57] with seemingly incidental ingestion of plant matter.[58] In the wild they have been observed to prey on crayfish, invertebrates, tadpoles, vegetation and carrion,[59] including dead fish and other animals.[39] Carr described having seen a chicken turtle eating Nuphar (bonnet-lily) buds,[56] while captive adults have been observed feeding on gopher frog tadpoles,[60] lettuce, and canned fish.[45] 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.[61] 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.[62] 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.[61]

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.[63] The length of the neck allows it to capture fast-moving prey such as fish and spiders, which would otherwise be able to escape.[39] Like Blanding's turtle (Emydoidea blandingii), the chicken turtle uses a sucking motion when feeding;[62] any water taken in during the process is expelled before the food is swallowed whole.[63] The Florida chicken turtle is known to feed passively, swimming along with an open mouth and foraging in clumps of vegetation.[62]

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.[45][62] Fire ants are also known to attack hatchlings of D. reticularia and other turtles.[64] Hibbitts and Hibbitts suggest humans and alligators to be the main predators of the western subspecies.[65] Snapping turtles are also listed as a possible predator.[48][62]

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;[37][56] it is thought that the vernacular name is a reference to the flavor of its meat.[49] It is still sometimes eaten today in rural areas, although this is uncommon.[45] Consumption by humans is no longer considered to be a significant threat to the chicken turtle.[64]