Sonoran mud turtle  (Kinosternon sonoriense)

Classified as Near Threatened (NT) on the IUCN Red List (1).

Although often appearing greenish in colour due to a covering of algae, the smooth, high-domed upper shell (carapace) of the Sonoran mud turtle is actually a uniform light or yellowish-brown (3), as is the shell beneath the body. The skin of the turtle is typically dark grey, with cream-coloured marks forming stripes from the eye along the neck (2). The neck also bears numerous small, nipple-like projections (4), and the turtle’s webbed feet indicate its mainly aquatic lifestyle (5). The male Sonoran mud turtle can be easily distinguished from the female by its longer and thicker tail, which possesses a horny nail at the tip (2) (3). Like other Kinosternon species, the Sonoran mud turtle is known to omit a strong musky odour when handled, a behaviour that has given these turtles the alternative name of ‘stinkpots’ (2).

Named after its occurrence in the Sonoran Desert, situated on the border of the USA and northern Mexico (6), the current range of the Sonoran mud turtle covers New Mexico and Arizona in the USA and the states of Sonora and Chihuahua in Mexico (2). It may be found at any altitude from sea level up to 2,042 metres (3).

The Sonoran mud turtle is a mainly aquatic species, principally found in the vicinity of streams, ponds, creeks or springs, sometimes situated in desert or grassland regions, but more often located within woodland (3). It has a preference for streams rich in aquatic invertebrates and with abundant underwater vegetation (5). 

Creeping slowly along the stream bottom, the Sonoran mud turtle forages primarily for invertebrates, such as worms, crustaceans and insects (2), but it has also been known to eat frogs and fish (3). It spends the majority of its life submerged beneath underwater objects (6), but periodically surfaces to breathe (2) and may sometimes leave the cold water to bask on land (7).

During cold periods, the Sonoran mud turtle may be active during the day, whereas during warmer summer months it is more frequently active during the night (2). Should the water in its habitat dry up during these hot periods, the Sonoran mud turtle may migrate up to eight kilometres to find a new water source (7), or aestivate (lay dormant) underground (6). The Sonoran mud turtle may also lay dormant to escape cold winter conditions in some parts of its range, hibernating in a crevice in the stream bank or in the muddy bottoms of a stream or pond (2).

The Sonoran mud turtle mates in March or April (5), and nests from May onwards (7) at sites away from the water (8). Females may lay up to four clutches of eggs each year, with each clutch containing up to 11 eggs (3). The first young turtles emerge from their eggs around August, with hatching continuing at least until late September, and maybe even until December in some areas (2). Female Sonoran mud turtles reach sexual maturity at six years of age, while males may reach maturity sooner, at between two and six years of age. The oldest individual recorded so far lived to at 13 years old (5).

The primary threat to this vulnerable species appears to be changes to its habitat. As it requires permanent or near-permanent water sources (5), reduced water levels, caused by droughts or groundwater pumping, decrease the amount of suitable habitat available. Human activities that change the natural fluctuations in water level, or decrease the vegetation on the stream banks, also affect the Sonoran mud turtle (5). It is also thought that juvenile turtles may be predated by invasive species such as bullfrogs and crayfish (5).

There are not known to be any active conservation measures currently in place for the Sonoran mud turtle, although a number of recommendations have been made. Surveys are necessary to identify mud turtle populations, before securing suitable habitat and attempting to protect the turtles from invasive predators (5). It has also been suggested that more research is conducted on this species’ reproductive biology and life history (5) (9), which will help inform future conservation measures for this secretive reptile.

View information on this species at the UNEP World Conservation Monitoring Centre.

To find out more about the conservation of mud turtles see:

• Arizona Game and Fish Department:
  http://www.azgfd.gov/w_c/mudturtlemanagement.shtml