The chicken turtle (Deirochelys reticularia) is a turtle native to the southeastern United States. It is the only extant member of the genus Deirochelys and is a member of the freshwater marsh turtle family Emydidae. The chicken turtle's scientific name refers to its extremely long neck and distinctive net-like pattern on its upper shell. There are three regionally distinct subspecies (eastern, western and Florida), which are thought to have evolved when populations became separated during periods of glaciation. These subspecies can be distinguished by their appearance; the western chicken turtle displays dark markings along the seams of its plastron (lower shell), while the plastron of the Florida subspecies is a bright yellow or orange color. Fossil records show that the chicken turtle has been present in the region for up to five million years.
Chicken turtles inhabit shallow, still or slow-moving bodies of water with plenty of vegetation and a muddy substrate. They are not found in rivers or deeper lakes that may be home to predators such as alligators and large fish. The chicken turtle is predominantly carnivorous and feeds mostly on invertebrates such as crayfish, dragonflies and spiders, but is also known to eat tadpoles, carrion and occasionally plant material. It is an active hunter and its long neck allows it to catch fast-moving prey. Although feeding and mating take place in aquatic environments, the chicken turtle is very well adapted to living on land and may spend more than half the year out of the water. Like many reptiles, it spends much of the day basking in the sun to regulate its body temperature, but unlike most other aquatic turtles, it hibernates over the winter months except in the warmer, southernmost reaches of its range.
The chicken turtle is relatively small compared to other related turtles, with males measuring up to around and females around . It is also one of the world's shortest-lived turtles, reaching a maximum age of 20–24 years. There are thought to be around 100,000 adult chicken turtles in the wild. Although the population as a whole is considered secure, its status in some areas is less certain and several states have listed it as threatened or introduced regulations to manage hunting or taking. The word "chicken" in the turtle's vernacular name is apparently a reference to the taste of its meat, which was once popular in turtle soup and commonly sold in southern markets.
Taxonomy and evolution
thumb|Drawing accompanying Latreille's 1801 description of Testudo reticularia
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 single 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)
The chicken turtle is the only extant species in the genus Deirochelys. Its parent family is Emydidae, the freshwater marsh turtles, which are found on every continent except Australia and Antarctica. 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 reticularia comes from the Latin for "net-like" or "reticulated" (reticulatus), probably alluding to the turtle's patterned carapace (top shell).
Subspecies
There are three distinct subspecies of chicken turtle, as described by Albert Schwartz in 1956 from a study of 325 specimens:
- 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 and females up to . It is distinguished from the other subspecies by the coloring of its carapace, which is olive to brown with a yellow rim. The plastron (lower shell) sometimes features a spot or indistinct splotch of color. Its outstretched neck is especially long, sometimes as long as the carapace itself.
- The Florida chicken turtle (D.r.chrysea) has the most distinctively patterned carapace of all the chicken turtles, featuring bold, broad yellow-orange reticulation. The shell is cuneiform (wedge-shaped), especially so in males and juvenile turtles, and measures up to for males and for females. The subspecies name chrysea is taken from the Latin for "golden one" due to the bright yellow or orange color of its plastron.
- The western chicken turtle (D.r.miaria) is the smallest of the three subspecies; males have a maximum carapace length of and females . The stripes on its head and neck are lighter in color (cream or pale yellow) compared to other chicken turtles, and its plastron features a dark pattern along the seams. The subspecies epithet miaria derives from the Greek for "stained", referring to this patterning. Its carapace is oval in shape and flatter than that of the other subspecies.
thumb|The [[plastron of the eastern chicken turtle (D.r.reticularia) sometimes features an indistinct splotch of color]]
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. Studies of the chicken turtle's mitochondrial DNA support this theory of earlier divergence of the western subspecies from the two eastern ones. 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.
Fossil record
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. Writing in 1978, Dale Jackson considered D.reticularia 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 (prior to the start of the Holocene, or Recent, epoch around 11,700 years ago) 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 relative, D.carri. This species was somewhat larger than its modern relative and its shell roughly twice as thick. Other fossil fragments from the Hemingfordian (20.6 to 16.3 million years ago) are considered to belong to even earlier, more primitive members of the genus.
Description
thumb|Large adult chicken turtle with the reticulated pattern on the carapace clearly visible
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. Although the chicken turtle shares morphological features with Blanding's turtle (Emydoidea blandingii), such as these elongated ribs and the shape of the skull, DNA analysis has shown they are not closely related.
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. West of the river, its territory reaches as far north as Missouri and as far west as Oklahoma and central Texas. Across its range, the chicken turtle may inhabit many hundreds or possibly thousands of wetland sites, although populations in any particular location are generally small. 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.
Florida chicken turtle
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.
Western chicken turtle
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. Its territory is also decreasing in Arkansas; 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 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.
Habitat
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 , but it is known to inhabit ponds up to 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 that 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.
Although the chicken turtle does not generally inhabit islands, isolated groups are also known in the Outer Banks chain of barrier islands off North Carolina. These maritime forest habitats are prone to drying out easily in the summer and can be affected by storms and sea spray, but research into one of these groups found no meaningful differences in longevity, growth rate or sex ratio between members of this population and their mainland counterparts.
Behavior
thumb|Chicken turtle basking
The chicken turtle is diurnal; its main periods of activity, such as feeding and mating, take place in the morning and late afternoon, either side of the warmest hours of the day. Turtles unable to find a suitable aquatic habitat during particularly dry years may migrate to higher ground and burrow into the earth to undergo aestivation, Chicken turtle mating takes place in shallow waters,
The female nests on land, often in loose soil, The mass appears to be positively correlated with female body size and eggs laid in fall are significantly heavier than those laid in spring. Several minutes after laying, the female will fill in her nest, sweeping the dirt over the eggs with her hind legs until they are covered. Chicken turtles commonly lay two clutches of eggs per year, although in the uninterrupted nesting season of Florida, females have been known to produce as many as four.
Growth and lifespan
The incubation period of chicken turtle eggs is again dependent on location and temperature. In the warmer climate of Florida, incubation takes 78–89 days in the wild, while in South Carolina it may last up to 152 days. Under laboratory conditions, which aimed to recreate the very cool soil temperatures (as low as ) experienced further north, incubation was extended up to 194 days. The egg's yolk contains a very high proportion of fats, on average 32.5% of dry matter, which help to nourish the hatchling during this long period in the nest. Wild chicken turtles have been recaptured up to 15 years after their first capture, with some reaching an estimated maximum age of 20–24 years. A study by herpetologist Whit Gibbons suggested that less than 1% of chicken turtles live past the age of 15. In captivity, they may only live for as little as 13 years. This short lifespan means that the average female chicken turtle is active for fewer than ten breeding seasons. Determining the age of a turtle becomes increasingly difficult as the animal ages; in the first few years of its life the turtle's shell may show visible growth rings (annuli) that can be used to approximate its age. Annuli in the turtle's claws can sometimes be seen up to the age of around 14.
Ecology
Diet
thumb|Dragonfly nymphs are a favorite food of the chicken turtle
Like many emydids, 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. lettuce, and canned fish.
In a 1997 study of chicken turtle fecal matter collected during the summer months in South Carolina, 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. Investigations into the digestive tract contents of chicken turtles in north-central Florida, where the eastern and Florida subspecies coexist, found similar results. Decapods (including crayfish and shrimp), dragonflies and beetles were the most frequently encountered foods; six out of twenty-five turtles had consumed trace amounts of plants or algae. Research in Oklahoma found evidence that adults of the western subspecies follow a more omnivorous diet than their relatives. While crayfish and bugs were still present in the majority of fecal samples, 92.6 percent of samples also contained material or seeds of various plants, including the common rush and broadleaf cattail.
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, relying on sight to detect its prey. 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, 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.
Predators
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 nests and kill hatchlings of D.reticularia and other turtles. Hibbitts and Hibbitts suggest humans and alligators to be the main predators of the western subspecies, while a study in Florida found evidence of red-shouldered hawks preying on various turtles including the Florida chicken turtle. Otters, herons and snapping turtles are also listed as possible predators. The trematode Neopolystoma orbiculare has been reported from the bladder of D.reticularia, while Telorchis corti is known to parasitize chicken turtles and various other emydids. A 2016 study of two chicken turtle specimens captured in Alabama identified a previously unknown species of blood fluke, Spirorchis collinsi.
Conservation
thumb|Chicken turtle in Virginia, where only around 30 adults are thought to remain
The chicken turtle population as a whole is currently considered secure and is thought to consist of at least 100,000 adults. where it is "extremely rare". In Missouri, where until 1995 no sightings had been recorded for at least 33 years, it is listed as an endangered species, making hunting illegal.