Gopherus morafkai

This is a typical land-dwelling tortoise with all the diagnostic external features: head is roofed with small unevenly sized scales; front feet are club shaped, scaled, and terminate in unwebbed toes with broad, thick claws; the hindlegs are columnar and elephantine, again with unwebbed broad claws; the carapace is highly domed, steep sided and flattened dorsally, brown (dull yellow to light brown in young), and has prominent growth lines; unhinged plastron is yellowish and generally has prominent growth lines; limbs are stocky; tail is short; adult carapace length 20-36 cm.

Compared to females, adult males average larger in size, have longer gular shields, a larger lump (chin gland) on each side of the lower jaw (especially in the spring), and a concave rather than flat plastron, especially in the posterior/femoral area (Stebbins 1985). Males have broader and thicker tails and thick toenails. Sexing individuals less than 15 years old and/or less than 200mm straight carapace length may be difficult by external morphology alone. See Rostal et al. (1994) for information on the use of plasma testosterone and laparoscopy to identify the sex of neonates (hatchlings) and immatures.

The age of juvenile tortoises up to approximately 20-25 years old may be determined by counting concentric annual rings radiating outward from the areolar center of each shell scute. The second right costal scute is recommended for age accounts. After 25 years shell wear and shedding of juvenile rings may obscure rings previously accrued (Germano 1988). However, such "growth rings" are annular only in localities in which plant forage growth is confined to a single season (Miller 1932). Areas with multiple peaks in primary production (driven by rainfall) in the Sonoran Desert, and captive raised tortoises, may exhibit multiple rings for a given year.

The eggs are pale, elliptical to spherical, brittle shelled, and relatively large (averaging 30-40 mm in diameter, and 20-40 g). Fertile egg shells usually become an opaque chalky white within the week following deposition, but become increasingly pink or gray and translucent if they are infertile or dead.

This species differs from box turtles (genus Terrapene) in lacking a hinged plastron and in having columnar hindlegs with flattened, rather than pointed and tapered, nails. Differs from the Texas tortoise (G. berlandieri) in having a single axillary scute on each side (rather than paired axillary scutes) and the 5th vertebral scute the broadest (rather than the 3rd). Differs from both the gopher tortoise (G. polyphemus) and the Mexican bolson tortoise (G. flavomarginatus) in having relatively larger hind feet (in the desert tortoise, the distance from the base of the first claw to the base of the fourth claw on the forefoot is approximately equal to the same measurement on the hind foot; in the bolson tortoise the measurement is smaller on the hind foot) (Ernst and Barbour 1989).

Box turtles and Texas tortoises have commonly been brought into the Southwest as pets. The southwestern box turtle (Terrapene ornata luteola) is the one terrestrial chelonian which now overlaps geographically and ecologically with the desert tortoise in the vicinity of Tucson, continuing east through Cochise County, Arizona. In recent years the Russian desert tortoise, Agrionemys (Testudo) horsfieldi has been imported by the pet trade in large numbers. While these tortoises resemble the North American species, their maximum size is a smaller 8" straight midcarapace length, their carapaces tend toward olive-gray rather than brown, and the forelimb toes number four rather than five. Other Eurasian tortoises are occasionally imported, but most have vivid carapace blotches of yellow, brown, or black, and/or a high domed rather than flattened top of the carapace.

Gopherus morafkai differs from G. flavomarginatus and G. polyphemus in having relatively smaller front feet. The distance from the bases of the first to fourth claws is the same on all feet in G. morafkai, whereas in the latter two species the distance from the bases of the first and third claws on the forelimb is about the same as the distance between the bases of the first and fourth claws on the hindlimb (Auffenberg and Franz 1978). Gopherus morafkai can be separated from G. berlandieri in having a rounded snout when viewed from above as opposed to a wedge-shaped snout in G. berlandieri (Auffenberg and Franz 1978). Also, the gular projections in G. morafkai normally do not diverge, and morafkai has a single axillary scale preceding each bridge, whereas in G. berlandieri the gular projections often diverge and the axillary scales are often paired (Murphy et al. 2011). Gopherus morafkai can be separated from G. agassizii in having a relatively narrower shell, shorter gular scutes, shorter projections of the anal scutes and in having a flatter, pear-shaped carapace (Murphy et al. 2011). Note that reliable identification of captive tortoises can be impossible due to hybridization or abnormalities resulting from poor nutrition.

This tortoise occurs in upland habitats of the Sonoran desert scrub (Brown et al. 1979) in areas with rocky outcrops and palo verde-saguaro cactus communities and ecoltonal desert grasslands (Van Devender 2002). Within these habitats, it generally occurs along rocky slopes, or bajadas, of desert mountain ranges (Murphy et al. 2011). Low density population occur along alluvial fans and in intermountain valleys where desert washes and associated caliche caves provide suitable habitat and shelters (Riedle et al. 2008, Grandmaison et al. 2010). These lowland population provide important linakes among disjunct mountain ranges (Edwards 2003, Edwards et al. 2004, Averill-Murray and Averill-Murray 2005).

Sonoran tortoises often retreat into rock crevices or small pallets wedged under boulders, rather than digging deep burrows. On the Florence Military Reservation in south-central Arizona, tortoises concentrated around incised washes with dense caliche caves or near a volcanic hill; tortoises selected incised washes over the other habitat types but apparently avoided washes with few caliche caves (Riedle et al. 2008). Thus availability of shelter sites may strongly influence tortoise distribution and abundance (Averill-Murray et al. 2002, Riedle et al. 2008).

Tortoises are often subterranean when inactive. Sonoran Desert winter dens are typically shorter than Sonoran summer dens (Vaughan 1984). In southeastern Arizona, hibernation dens were primarily on steep south-facing slopes and were often associated with live vegetation, dead or downed vegetation, and/or packrat nests; dens varied in length depending on the sex of the occupant (Bailey et al. 1995). Barrett (1990) also found that tortoises in the Sonoran Desert of Arizona hibernated in steep rocky slopes.

Pallets are shallow excavations which often barely cover the tortoise. They provide common summer shelters throughout most of the range and are used as winter shelters only in the southern lowlands (Aufffenberg 1969). Pallets generally are placed under the cover of shrubs. Summer burrows and pallets are particularly fragile and vulnerable to the erosive effects of livestock hoofs, rodent excavation, wind, and rain (Coombs 1977).

Multiple burrow use is common in tortoises, with several burrows utilized by one individual in a single week. In Arizona, individuals used an average of 7.6 dens (Barrett 1990). Winter dens commonly are shared, and even summer burrows temporarily may be cohabited. Therefore, a count of active burrows may not accurately represent local population numbers or densities.

Eggs are laid in shallow depressions, often 3-4 inches deep. In one site in the Sonoran Desert, Arizona, all eggs and hatchlings were observed in washes (Barrett 1990). Nests usually are placed in well-drained, friable soils.

The Sonoran Desert populations are patchy (Dodd 1982), occurring on montane foothill islands, but a few southern Arizona sites (5% of total) sustained tortoise densities in excess of 300/sq mi (Burge 1980).

Primary sources of mortality in Arizona include falls in steep rocky habitat, being overturned during combat or mating, and predation by mountain lions (Puma concolor) (Reidle et al. 2010).

A number of organisms are intimately associated with desert tortoise burrows (summarized by Grover and DeFalco 1995): ground squirrels, Peromyscus and pocket mice, kangaroo rats, woodrats, jackrabbits, desert cottontail, domestic cat, spotted skunk, kit fox, burrowing owl, Gambel's quail, poorwill, roadrunner, desert gecko, desert iguana, desert spiny lizard, western whiptail, gopher snake, coachwhip, night snake, Mohave rattlesnake, sidewinder, western rattlesnake, antlion larvae, ground beetles, roaches, silverfish, black widow spider, tarantula, and ticks.

As a result of their unfavorable surface to volume ratio and the high metabolic rate, smaller tortoises are more vulnerable to dehydration (and starvation) than are older/larger individuals. The younger age classes are particularly vulnerable to short-term habitat degradation (occasional overgrazing by livestock) and drought. Immatures lack the lipid reserves and the proportionately larger urinary bladder that allow adults to endure several years of drought with very little effect on physiological homeostasis and reproduction.

Tortoises are effective in retaining water under desert conditions. They have some capacity to switch from water-demanding urea to more conserving uric acid for nitrogen waste elimination when such conservation is needed. In addition, they are more vulnerable to water loss during surface activity when their eyes are open, pulmonary gas exchange is rapid, and the head is extended than when resting or hibernating in a burrow (see Cloudsley-Thompson 1971, Minnich 1977, Schmidt-Nielsen and Bentley 1969, and Nagy and Medica 1986).

Ravens, along with coyotes, feral dogs, and cats are "subsidized" predators that have semi-urban populations enlarged by feeding on the refuse and rodents associated with human garbage dumps and backyards. They may be significant predators on young (< 7 years old or 120 mm plastron length) tortoises. However, in the south-central Mojave Desert, Bjurlin and Bissonette (2004) found that neonatal desert tortoises (G. agassizii) are less susceptible to predation than was previously thought, perhaps because of their cryptic coloration and secretive habits. The common raven was not found to be a source of neonate mortality.

Courtship and breeding occur in July-September (Averill-Murray et al. 2002). Adult females produce a single clutch in late spring every 1-2 years (Averill-Murray 2002). Clutch size is 1-12 (mean around 6) (Averill-Murray 2002).

Estimate of mean age of sexual maturity was 15.7 years in the Sonoran Desert (Germano 1994). Tortoises with straight plastron midline lengths larger than 200 mm are generally sexually mature, including males in which plastron concavity is not conspicuous.