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Pseudemys texanaTexas River Cooter

By Kendra Earls

Geographic Range

Texas river cooters (Pseudemys texana) are native to the Nearctic region, strictly in central and south-central Texas. Their range is limited to the Brazos, Colorado, Concho, Llano, San Saba, Guadalupe, Neuces, and San Antonio watersheds. (Ernst and Lovich, 2009; Etchberger and Iverson, 1990; van Dijk, 2011)

Habitat

Texas river cooters are aquatic animals. They are normally found in the shallow water of freshwater rivers, but they can enter riverine pools as deep as 4m. River cooters have also been observed in lakes with sewage sludge. They can also inhibit riverine impoundments, nearby cattle tanks, canals, and irrigation ditches. River cooters are most commonly found in clear water with soft, dense vegetation beds or in wetlands near their permanent water source.

Before laying eggs, female cooters move onto land and dig a nest. Most cooters nest in mixed short-grass areas. Nests on bare soil and mulch have also been observed. Most nests had no cover while the remaining nests were located near trees, landscaping, and manmade structures. Washington (2008) observed the distance from the water to nesting sites and the average temperatures of soil and air during nesting. She reported that these turtles dug nests 14.63 to 153.63m from water. Recorded air and water temperatures were 23.9°C to 35.2°C and 21.9°C to 28.3°C, respectively.

On moderately hot days, Texas river cooters use fallen trees and broken branches on the shoreline for basking in the sun. Hill (2008) reported that temperature range for basking was between 25.3 to 46.8 °C. In cooler weather, Texas river cooters use the shoreline to hibernate. (Coleman, 2008; Ernst and Lovich, 2009; Hill, 2008; Lindeman, 2007; van Dijk, 2011; Washington, 2008)

  • Aquatic Biomes
  • rivers and streams
  • Range depth
    4 (high) m
    13.12 (high) ft

Physical Description

Texas river cooters possess narrow yellow head striping with spots and dashes. Their skin is black with yellow and white striping. A singular stripe curves around their jaw with a yellow spot behind the eye. Their brown carapace is flat in the middle and scored around the edge with fine yellow webbing and swirls for coloring. Their plastron has little, if any, pattern in older river cooters, but the rim may have a red tint. River cooters can become melanistic as they age. Male river cooters have a thicker tail and their vent is behind the carapacial rim. The carapacial rim is part of the carapace that covers the plastron. Female river cooters have shorter tails and their vent is anterior to the carapacial margin. Male river cooters have longer and more noticeable foreclaws than female cooters.

Adult male river cooters are shorter and flatter than female cooters. Lindeman (2007) reported the body size of adult male and female river cooters across their range. Male cooters had an average carapace length (CL) of 142.4mm (range of 89-191mm CL). Despite this large range, males’ carapace lengths rarely exceeded 170mm. Mature males' average plastron length (PL) was 122.9mm (range 78 to 161mm PL). Linden (2007) reported that female river cooters' average carapace length was 245.9mm (range 223-274mm CL), while their average plastron length was 223.1mm (range 213-241mm PL).

The carapace on juveniles is the same brown color as adults. The pattern is lighter than adults with five or six obvious lighter yellow rings and swirls. The pattern will diffuse and texturize with age. The plastron is yellow with thin black lines on the edges. Lindeman (2007) measured unsexed hatchlings and reported an average carapace length of 48.0mm (range of 41-53mm CL). At one year old, these same turtles recorded an average carapace length of 69.0mm (range 60-78mm CL). At two years old, these turtles had an average carapace length of 74.0mm (range 60-84mm CL). The plastron of unsexed hatchlings averaged 45.0mm (range 41-53mm PL). After a year, the same turtles had an average plastron length of 61.2mm (range 54-66mm PL). At two years of age, they had an average plastron length of 66.0mm (range 55-75mm PL). (Buhlmann, et al., 2008; Ernst and Lovich, 2009; Etchberger and Iverson, 1990; Lindeman, 2007)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    89 to 274 mm
    3.50 to 10.79 in

Development

Texas river cooters rely on temperatures in the nest for sex determination. Males are produced in colder nest temperatures while females are produced in warmer nests. Nests with a temperature between 21.5°C and 27°C predominately produce males. Temperatures between 27.5°C and 29.5°C produce mixed sex ratios. Only females are produced in nest temperatures at or above 29.6°C. Texas river cooters’ incubation time is between 80 and 150 days. This time varies based on the temperature, covering, and the amount of water. Large amounts of water in the nest are found the increase the incubation time. Nests with a smaller temperature tend to have more covering and an increased incubation time.

They grow indeterminately, meaning they continue to grow throughout their lives. Male hatchlings have an estimated plastron length of 34mm while female hatchlings have an estimated plastron length of 24mm. Male river cooters are mature at 3 years old or when their plastron length is larger than 78mm. Females are considered mature after 6 or more years and when their plastron length is larger than 233mm. Female river cooters have a growth rate of 0.129mm per year while males' growth rate is 0.191mm per year. (Ernst and Lovich, 2009; Lindeman, 2007; Valenzuela and Lance, 2004; Washington, 2008)

Reproduction

Female Texas river cooters use pheromones to attract potential mates. Mating begins in early spring in March and April. The males will sniff the females’ cloaca when looking for a mate. Males will shake their foreclaws and extend their forearms to attract female cooters. Texas river cooters are polygynandrous, meaning males and females have multiple partners in their lifetime. (Gans and Crews, 1992)

Texas river cooters begin mating in early spring, in March and April. They nest from May until June. Gestation period for river cooters is estimated from 60 to 70 days. Female cooters lay between 0-3 (typically 1) clutches of 4-19 eggs during this period. Larger females lay larger clutches. Females have only been observed nesting diurnally. The process of leaving the water, ovipositing, and returning to the water takes the females 2.5-3 hours. August and September are when hatchlings will emerge. The eggs incubation period ranges from 80-150 days; this range can be affected by the amount of water and nest temperature. Birth mass is not reported but lengths at hatching are estimated: average plastron lengths of 34mm for males, and 24mm for females. These turtles are immediately independent at hatching. Male cooters are sexually mature at 3 years old, while females can take 6 or more years to mature. (Ernst and Lovich, 2009; Rose, 2011; Rose, et al., 1996; Washington, 2008)

  • Breeding interval
    River cooters breed once yearly.
  • Breeding season
    Egg laying occurs in late May and June. Incubation period is 80-150 days.
  • Range number of offspring
    4 to 19
  • Range gestation period
    60 to 70 days
  • Range time to independence
    0 (low) minutes
  • Range age at sexual or reproductive maturity (female)
    6 (low) years
  • Range age at sexual or reproductive maturity (male)
    3 (low) years

Female river cooters have very little parental investment after nesting. They make the choice to place the nest near the water’s edge or farther away. Male rivers cooters are only present for mating. (Washington, 2008)

  • Parental Investment
  • no parental involvement
  • pre-hatching/birth
    • provisioning
      • female

Lifespan/Longevity

The maximum lifespan of Texas river cooters is unknown. Texas river cooters probably have similar longevity to river cooters (Pseudemys cocinna), which is 44 years. Texas river cooters can also be kept in captivity, but lifespans have not been reported.

Mortality rate for eggs is high in wild populations. Washington (2008) found 59.2% predation on nests was by raccoons (Procyon lotor). Only 45.65% of protected nests produced hatchlings. (Ernst and Lovich, 2009; Washington, 2008)

  • Typical lifespan
    Status: wild
    44 (high) years

Behavior

Texas river cooters are diurnal. These turtles usually bask alone, but site size and orientation can contribute to basking in groups. Hill (2008) observed the effects of urbanization on basking. Many turtles chose areas with high shoreline modification. These modified shorelines had less woody vegetation. They also chose to avoid areas with high daily human disturbance.

During the mating season, the males will shake their claws and extend their forearms to attract mates. The female river cooters emit pheromones the male can smell from her cloaca. If the male senses these pheromones, he will mount the female. Before laying eggs, female cooters move onto land and dig a nest.

Between seasons female river cooters migrate longer distances than males. Franklin (2006) reported that females migrated about 289.42m from their fixed locations while males migrated 163.14m. Texas river cooters are a diurnal species. They do not hibernate, but their metabolic rate is relatively slow during colder weather. (Franklin, 2006; Hill, 2008; Kramer, 1995; Washington, 2008)

Home Range

Texas river cooters' home range is about 650m including land on which they bask. Females' ranges are larger (3.77ha) than males (2.06ha), but their ranges overlap. Between seasons female river cooters migrated greater distances than males; females migrated about 289.42m from their fixed locations while males migrated 163.14m. Texas river cooters are not territorial. (Franklin, 2006; Kramer, 1995)

Communication and Perception

All reptiles have pheromones. Aquatic turtles have two primary spots where these will emit: the chin glands and the cloaca. When looking for mates, males will chase and sniff the females’ cloaca. River cooters receptor cells likely function similar to the pond slider (Trachemys scripta). Their receptor cells contained high levels of galactosamine sugar residues. These residues functions as the pheromone signal.

The courtship in turtles involves titillation. Titillation is when the males extend their forearms and vibrate their foreclaws in front of the female. The female will choose if he is suitable to mate. They also use tactile efforts to forage, dig nests, and bask. Turtles perceive the world in color. They have a pigmented oil that allows for color vision. (Gans and Crews, 1992; Seidel and Ernst, 1996; "Turtles Are Key To Tracing Birds' 'Redness Gene' Back To The Dinosaurs", 2016)

Food Habits

Adult Texas river cooters of both sexes are primarily herbivorous when mature. The main plants in their diet are hydrilla (Hydrilla verticillata), Carolina fanwort (Cabomba caroliniana), parrot feather (Myriophyllum), common coontail (Ceratophyllum demersum), delta arrowhead (Sagitaria platphylla), cone-spur bladderwort (Utricularia gibba) and filamentous green algae (Chlorophyta). Fields et al. (2003) reported stomach contents of river cooters. They found parrot feather (Myriophyllum) was present in 90.9% of stomach samples, Hydrilla verticillata in 87.9%, Cabomba caroliniana in 78.8%, and Ceratophyllum demersum in 57.6%. In the stomach contents, 2.1% of their diet was unknown vegetation (2003). Leaves from the plants are the most often consumed.

Juveniles have a more carnivorous diet than adult river cooters. Common prey eaten by juvenile river cooters includes freshwater sponges (family Spongillidae), aquatic insect larvae like mayflies, crayfish (order Decopoda), snails (order Gastropoda) and small freshwater clams (Sphaerium). (Etchberger and Iverson, 1990; Fields, et al., 2003; Lindeman, 2007)

  • Animal Foods
  • insects
  • mollusks
  • aquatic crustaceans
  • other marine invertebrates
  • Plant Foods
  • leaves
  • algae

Predation

Raccoons (Procyon lotor), skunks (family Mephitidae), and red imported fire ants (Solenopis invicta) are nest predators. Additional predators at any age include red foxes (Vulpes vulpes), striped skunks (Mephitis mephitis), laughing gulls (Larus atricilla), American crows (Corvus brachyrhynchos) and raccoons.

Raccoons are recorded as the most prolific nest predator for Texas river cooters. Fire ants also prey on female river cooters on land and actively digging nests. Irritation from the fire ants may cause the female river cooters to stop nesting and return to the water, keeping them from completing the nesting process. River cooters’ first line of defense is to flee and try to escape from the predators; if they are unsuccessful, they may bite or retreat into their shells. Humans (Homo sapiens) are also predators of Texas river cooters. It is not uncommon for turtles to be hit by cars. Male cooters are less like to die from road mortality as they do not travel on land as often as females. (Ernst and Lovich, 2009; Washington, 2008; Whiting, 1994)

Ecosystem Roles

Texas river cooters are a mainly herbivorous species. Their predators include red foxes (Vulpes vulpes), striped skunks (Mephitis mephitis), laughing gulls (Larus atricilla), American crows (Corvus brachyrhynchos) and raccoons (Procyon lotor).

Nordemeyer et al. (2020) examined Texas river cooters for parasitic protozoan in red blood cells. They identified 80 apicomplexan (Haemogregarina) parasitic infections, primarily in wild cooters. During breeding, these parasites can be transferred to other populations, including captive turtles. River cooters have been observed basking with turtles of other species, which can transfer diseases and parasites. Texas river cooters can also be parasitized by ticks (Ixodidia) and leeches, which can transmit diseases. (Ernst and Lovich, 2009; Hill, 2008; Nordemyer, et al., 2020; Washington, 2008)

Commensal/Parasitic Species
  • apicomplexan (Haemogregarina)

Economic Importance for Humans: Positive

Texas river cooters can be kept as pets. They usually cost between $30 and $100 dollars. However, commercial collection of river cooters from Texas waters stopped in 2007. River cooters are also hunted and eaten in the southern United States. There are no restrictions on hunting. (Gaertner, et al., 2008; Knodler and Elfenbein, 2020; van Dijk, 2011)

Economic Importance for Humans: Negative

Texas river cooters can carry Salmonella enterica, which can cause illness in humans. Salmonella can be found in both captive and wild turtles. Salmonella can cause abdominal pain, vomiting, diarrhea, and fever in humans. (Gaertner, et al., 2008; Knodler and Elfenbein, 2020)

Conservation Status

Texas river cooters are considered a species of “Least Concern” on the IUCN Red List. They have no special status on the US Federal List, CITES, or the State of Michigan list.

These freshwater turtles face habitat loss, degradation, and invasive species. Red imported fire ants (Solenopis invicta) are a direct threat to nesting cooters and their eggs. Fire ants can kill the hatchling or enter the egg through any impurities and kill them. Humans are also a threat to Texas river cooters. They are hunted for food and can also be hit by cars. There is no restriction on hunting.

Although their populations appear stable, the commercial collection of river cooters was stopped in 2007. van Dijk (2011) recommended monitoring at representative locations to allow for more research of their natural history and their conservation needs. Because Texas river cooters tolerate human disturbance, Vermersch (1992) speculated the creation of impoundments and other vegetated waterbodies actually increased their abundance. He also found river cooters were more abundant in 1992 than the 1960’s in the San Antonio River, despite pollution. (Hill, 2008; van Dijk, 2011; Vermersch, 1992)

Contributors

Kendra Earls (author), Radford University, Karen Powers (editor), Radford University, Victoria Raulerson (editor), Radford University, Christopher Wozniak (editor), Radford University, Genevieve Barnett (editor), Colorado State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

visual

uses sight to communicate

References

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