Kinosternon sonoriense

Geographic Range

Sonora mud turtles ( Kinosternon sonoriense ) are found in or near rivers throughout the southwestern United States and northwestern Mexico. Their geographic range includes the southeastern tip of Nevada, near the Colorado River, south to the southwestern edge of Chihuahua, Mexico, around the Yaqui River. They live from Nevada through parts of central and southeastern Arizona and to Catron County, New Mexico. They are absent from Utah, Colorado, and Texas.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Sonora mud turtles live in various bodies of water such as streams, shallow pools and even large puddles with depths of 20 to 300 cm. These bodies of water are usually permanent, but they have also been found in waters that dry completely during the summer months. Turtles have been observed in bodies of water in arid mountain and desert areas, between elevations of 305 to 1,525m (average 500m). In the past, Sonora mud turtles were believed to be entirely aquatic, but recent studies have identified terrestrial movement. Turtles will occasionally move through desert or mountainous terrain to get from one body of water to others up to 300m away. However, it is currently unclear why or how long Sonora mud turtles remain on land.

During periods of drought, Sonora mud turtles burrow into sand or dirt and estivate until water returns. Studies have shown that they can survive on land without food or water for at least 80 days. Sonora mud turtles are also known to hibernate on land during winter months.

• Habitat Regions
• terrestrial terrestrial
• freshwater freshwater

• Terrestrial Biomes
• desert or dune desert or dune
• mountains mountains

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• temporary pools

Physical Description

Sonora mud turtles are small, primarily aquatic turtles with light, olive-green to olive-brown shells, which are mottled with dark spots. They have yellow plastrons and greyish-black legs. The lateral edges of their front legs usually have a yellow line. They have green-grey heads, with dark stripes on the sides and dark spots on both their chins and the top of their heads. As adults, their carapaces measure 75 to 150 mm and they reach body masses of 161 to 351 g. One study from 1990 reports the shell shape of adult Sonora mud turtles as unique to their species, but the study does not describe the shell shape itself. However, juveniles have shells similar in shape to those of juvenile Mexican mud turtles ( Kinosternon integrum ). Juveniles are also usually darker in color than adults and have dark black lines along the edge of their carapaces. Hatchlings range in carapace length from 15 to 25 mm and juveniles range in carapace length from 25-to 93 mm.

Sonora mud turtles exhibit subtle sexual dimorphism in size, coloration, and tail length. Males are generally smaller than females and grow more slowly throughout their lives. Ventral melanism, or the increased development of pigment on their underbellies, is more common in males than females, as is dark mottling on the jaw. Males also have longer tails in proportion to their carapaces. Additionally males have concave plastrons and two rough patches on the medial areas of each hind leg, which is assumed to aid in mating. Females lack these rough patches and have flat plastrons.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes colored or patterned differently

Development

Sonora mud turtle females lay eggs from April to September. Eggs are usually 17.8 to 21.7 mm in width with an average of 19.4 mm. Sonora mud turtles hatch in mid-July and are between 20 and 33 mm in carapace length. Hatchlings undergo rapid growth as soon as they emerge. By mid-August, hatchlings reach approximately 40 mm carapace length and are considered juveniles. After reaching 40 mm carapace length the average growth rate of young turtles slows to 12.9 mm per year. Upon reaching sexual maturity, average growth rate drops to about 1.50 mm per year, which continues indeterminately until death.

Sonora mud turtles reach sexual maturity when they are around 70% of their maximum size. Male turtles typically reach sexual maturity around 7 years of age, whereas females reach maturity at age 9 or 10. At sexual maturity, male Sonora mud turtles have an average carapace length of 121 mm and females 142 mm. Males grow slower than females on average, and they reach a smaller final size. However, diet quality affects growth rates for overall populations of Sonora mud turtles. In populations where food for adults is limiting, turtle growth rates slow down 2 to 5 years sooner than in populations where food is not limiting.

A study from 2010 reported the average growth rate of hatchlings, as measured by carapace length, to be 51.09 mm per year. This study also found that within the first three months after hatching, Sonora mud turtles in central Arizona typically added two plastron annuli. After these three months, turtles added only two plastron annuli per year. Hensley proposed that this was due to the area having two seasons in which there was heavy rainfall each year. The turtles typically grow faster during rainy months. The change between growth rates seasonally is what causes the formation of plastron annuli. This finding is contrary to the assumption that each turtle adds one plastron annuli per year, and suggests that previous age estimations based upon number of plastron annulus may have been inaccurate.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

Sonora mud turtles breed from March to April each year. Usually, males seek out and mate with as many females as possible. Males locate females through their sense of smell, which they use to detect pheromones released by females. Females usually lay one to two clutches of eggs per year but they do not necessarily lay eggs every year. In a study from 1982, the ratio of mature males to females was almost 2:1 in central and southern Arizona. This report suggested that this skewed ratio is the result of faster maturation of males.

In winter, sperm production in male Sonora mud turtles slows to a halt, only becoming active again in spring. However, males store sperm in their vas deferens during the winter months to allow for earlier mating events in the spring. Females generally ovulate between April and September.

• Mating System
• polygynous polygynous

Sonora mud turtles breed from March to April. They are oviparous and lay eggs from April to September, though they lay most of their eggs in June and July. A 1982 study found that, in populations at higher elevations, around 1,200 m the egg laying season ended in July. Male turtles store sperm in their vas deferens during winter months so they can breed earlier in spring, before their reproductive systems are fully active again. The amount of clutches they lay per year varies by population, and females do not necessarily lay eggs every year. A report in 2012 from central Arizona found that females only laid one clutch per year, whereas a study from 1982 found that females in central and southern Arizona laid two clutches per year. It is neither understood how these populations differed from each other, nor what factors effect the number of clutches females lay per year. Typically, each clutch contains 1 to 11 eggs, with an average of 5. Generally, clutch size increases with increasing latitude and egg size decreases with latitude. Also, the amount of eggs a female lays per clutch is weakly positively correlated with the carapace length of that female. The gestation period of Sonora mud turtles has not yet been researched.

Eggs hatch in fall and hatchlings measure about 15 to 25 mm in carapace length, and are immediately independent from their parents. Males become sexually mature at around 7 years of age and females around 9 years of age. Both sexes mature when they reach about 70% of their maximum size.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Sonora mud turtles exhibit little parental investment, although females dig burrows for their eggs. Females exhibit no further parental investment after digging nests and laying eggs. Males exhibit no parental investment beyond the act of mating.

• Parental Investment
• no parental involvement

Lifespan/Longevity

There is limited information on the lifespan of Sonora mud turtles. A study in 1992 recorded the maximum lifespan of a captive Sonora mud turtle is 36.5 years. There are no known reports of lifespans for wild Sonora mud turtles.

Behavior

Sonora mud turtles are solitary and show little interaction with conspecifics outside of breeding season. However, they often share overlapping home ranges and may sometimes reside in areas with remarkably high population densities. A study from 2001 found the average population size of Sonora mud turtles to be 212 individuals. Population densities for turtles are usually expressed as the number of individual per hectare of water surface. Population densities have been measured as low as 188/ha to as high as 8,829/ha. Population density is likely strongly influenced by water availability. A 2020 study found a weak positive correlation between population density and elevation.

Sonora mud turtles are most active during summer monsoon seasons and are the least active during winter. They have been observed hibernating from October to February. Turtles often undergo terrestrial brumation, even when temperatures are mild and there is available water. This suggests that hibernation is linked to food abundance more than temperature or water availability.

Sonora mud turtles are mainly aquatic turtles but they also display some terrestrial activity. Often, turtles living in habitats with shallow water will flee onto land when there are disturbances in the water. One study in 2011 found that larger turtles are more likely to flee, possibly because it is more difficult for larger turtles to conceal themselves in water.

Sonora mud turtles often make long distance movements (greater than 100 m) over land between pools of standing water, either within streams, or stand-alone ponds. There are many factors affecting these movements including mate-seeking, drought, nesting activity, avoidance of predators, movement between foraging areas, and estivation or brumation. It is generally agreed upon that some amount of long distance movement is present in every population of Sonora mud turtles. No pattern has yet been detected concerning direction of movement upstream or downstream.

Overall, male Sonora mud turtles show more movement and have larger home ranges than females, and they are more likely to move between pools and to make long-distance movements (over 500 m). Males are most active from May through September and are more likely to wander from their home pool during mating season. Occasionally male movement is restricted to areas with high concentration of females during mating seasons. One 2007 study found that male turtles spend about 37% of their time in their home pools and will share home pools with other males around 3% of the time. It is more likely that Sonora mud turtles will share pools during times of drought.

Females are most active from August to October and much of their movement happens following summer rains when they move to nesting sites. Younger females show more movement than older females and there is a positive correlation between time spent in home pools and carapace length. A study in 2007 found that medium-sized females (100 to 188 mm carapace length) spent about 47% of their time in their home pools and large females (greater than 188 mm carapace length) spent 74% of their time in home pools. Large females will only leave their home pools to estivate or build nests, or if the water source dries up completely. However, they return to their home pools when possible. It is much more common for medium-sized females to share home ponds with other females because their home ranges overlap with other medium females about 40% of the time. Large female turtles rarely share home pools with medium-sized females and almost never with other large females. It is not yet understood if large females will actively protect their home pools or if they simply avoid ponds with other females. Sonora mud turtles are not currently considered territorial.

Adult turtles move more frequently than juveniles, which usually reside in one pool until they reach sexual maturity. A study from 2010 found that juvenile turtles (40 to 76 mm in carapace length) on average made movements of 99 m and hatchlings (less than 40 mm in carapace length) only 5.4 m. At the onset of sexual maturity, Sonora mud turtles begin to move more often.

Drought tolerance of Sonora mud turtles varies between populations and is largely influenced by the amount of permanent water available in the habitat. A study in 2002 subjected Sonora mud turtles from different populations to drought in a lab environment and found that individuals from areas with fewer permanent water sources reduced their activity levels more. This suggests that individuals from drier areas are better adapted to conserve energy during times of drought. A study in 2007 found that wild Sonora mud turtles estivate in vegetation, soil, or other organic matter 64% of the time, and in the crevices of boulder piles 36% of the time. They likely prefer to estivate in organic material, as it better preserves humidity and limits water loss during times of high heat or drought. A study from 2003 proposed that estivation is the most common response to drought in the species and showed that turtles can remain dormant on land for 11 to 34 days. However, a study in 2010 observed turtles estivating on land even when water was available, which suggests that there are more factors influencing estivation than we currently understand.

Sonora mud turtles show less movement during drought years than in non-drought years and turtles in habitats with ephemeral bodies of water make more long distance movements. Turtles residing in habitats with permanent bodies of water show very little terrestrial activity. This suggests that water availability is one of the factors influencing movement.

• Key Behaviors
• natatorial natatorial
• motile motile
• hibernation hibernation
• aestivation
• solitary solitary

Home Range

Home range sizes for Sonora mud turtles depends on the age, size, and sex of the individual turtle. A 2007 study found that adult male turtles had the largest home range with an average of 3.33 ha. Adult females had an average home range of 0.13 ha. Size and age have an effect on home range size for female Sonora mud turtles especially. Younger mature female turtles had an average home range of 0.50 ha, while older mature females had a smaller home range of 0.05 ha or only 530 m^2. Because Sonora mud turtles grow continuously throughout their lives, female home range size is negatively correlated with age and carapace length.

Communication and Perception

Sonora mud turtle are mostly solitary. They are known to share bodies of water with other turtles, but they do not frequently interact except with conspecifics during breeding season. Sonora mud turtles possess musk glands on their heads, which secrete sex-specific chemicals. Generally, males seek out reproductively available females by smelling these chemicals. Males often approach females from the rear and smell them to confirm their sex. In order to express their interest in an individual female, males begin nudging and biting at the female. Most communication between turtles is either through smell or touch. Sonora mud turtles rely most heavily on smell and sight for hunting.

• Communication Channels
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Sonora mud turtles are opportunistic omnivores, often foraging in shallow water. They eat snails, fish, frogs, snakes, crayfish, and a large variety of aquatic and semi-aquatic insects. Sonora mud turtles have been directly observed eating red spotted toads ( Bufo punctatus ), black-necked garter snakes ( Thamnophis cyrtopsis ), and ground snakes ( Sonora semiannulata ). Recent studies have shown that Sonora mud turtles also occasionally eat lizards - specifically Arizona alligator lizards ( Elgaria kingii nobilis ). Sonora mud turtles also eat aquatic vegetation, especially in areas with denser turtle populations, where competition for ideal prey species is higher. A 1974 study reported that the diet of Sonora mud turtles includes around 18.3% plant material by volume, including angiosperms and chlorophyta. The exact types of plants that Sonora mud turtles eat varies by location. They will also opportunistically consume carrion, although they more typically hunt live prey. In times of drought, Sonora mud turtles can survive at least 80 days without food or water.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
• omnivore omnivore

• Animal Foods
• amphibians
• reptiles
• fish
• carrion carrion
• insects
• mollusks
• aquatic crustaceans

• Plant Foods
• leaves
• algae

Predation

Adult Sonora mud turtles have very few natural predators and are most vulnerable as hatchlings or juveniles. A study from 2010 found that virile crayfish ( Orconectes virilis ), an invasive species, were the main predator of hatchlings in central Arizona. Statistical analysis found a significant increase in juvenile and hatchling survival rates when virile crayfish were completely eliminated from the study area. A study from 2001 proposed that mammals and birds may be predators of Sonora mud turtles, although they did not name any particular mammal or bird species.

Ecosystem Roles

Sonora mud turtles have been found to host two species of parasitic leeches, Erpobdella punctata and Placobdella rugosa . They are also mutualists with different algae, including Basicladia chelonum , Blasicladia crassa , and species in the genus Dermatophyton . Sonora mud turtles have shells that provide a safe growing area for the algae, and the algae serves as camouflage for the turtles. Younger Sonora mud turtles typically have less algae growing on their shells, likely because their shell surface is smoother than adults.

Sonora mud turtles are known to prey upon snails, fish, frogs, snakes, lizards, crayfish, and aquatic or semiaquatic insects. They may play a role in controlling populations of their prey items. Young Sonora mud turtles often fall prey to virile crayfish ( Orconectes virilis ), and thus serve as a food source for an invasive species.

Economic Importance for Humans: Positive

Sonora mud turtles have little to no economic impact on humans. According to the IUCN Red List, they are occasionally collected for the pet trade, but this rarely happens so they do not have a large role in the pet trade economy.

• Positive Impacts
• pet trade pet trade

Economic Importance for Humans: Negative

There are no known negative impacts of Sonora mud turtles on humans.

Conservation Status

In 1996, Sonora mud turtles were listed as a threatened species, but studies have since revealed that they exist in larger numbers than initially expected. Sonora mud turtles are currently considered "near threatened" on the IUCN Red List. They have no special status on any other national or international conservation list.

Threats to Sonora mud turtle populations include the introduction virile crayfish ( Orconectes virilis ), an invasive species which preys on hatchlings and juveniles. Their populations are also under threat from irrigation and water extraction projects, which further limit the amount of available water in an already arid environment. In an effort to protect Sonora mud turtles, Arizona and New Mexico have put limits on collection of turtles from the wild. New Mexico has an annual limit of individuals that may be collected, whereas Arizona has completely banned collection.

Populations of Sonora mud turtles exist in protected state parks of Arizona. These areas offer natural habitats that benefit Sonora mud turtles and are remote enough that human disturbance is infrequent. Many organizations in Arizona, including the Arizona Game and Fish Department and the Phoenix Zoo, work together to improve habitat quality and maintain captive breeding populations of Sonora mud turtles.

Additional Links

Encyclopedia of Life

Contributors

Lindsey Wagner (author), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Emily Clark (editor), Radford University, Cari Mcgregor (editor), Radford University, Jacob Vaught (editor), Radford University, Galen Burrell (editor), Special Projects.

References

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Hensely, F., T. Jones, M. Maxwell, L. Adams, N. Nedella. 2010. Demography, terrestrial behavior, and growth of Sonora mud turtles (Kinosternon sonoriense) in an extreme habitat. Herpetological Monographs , 24/1: 174-193.

Hulse, A. 1976. Carapacial and plastral flora and fauna of the Sonora mud turtle, Kinosternon sonoriense Le Conte (Reptilia, Testudine, Kinosterdae). Journal of Herpetology , 10/1: 45-48.

Hulse, A. 1974. Food habits and feeding behavior in Kinosternon sonoriense. Journal of Herpetology , 8/3: 195-199.

Hulse, A. 1976. Growth and morphometrics of Kinosternon sonoriense (Reptilia, Testudines, Kinosternidae). Journal of Herpetology , 10/4: 341-348.

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Iverson, J. 1978. Distributional problems of the genus Kinosternon in the American Southwest. Copeia , 1978/3: 476-479.

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