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Sonoran Desert Tortoise (Gopherus morafkai)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”186″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Sonoran Desert Tortoise. ©2013 Dancing Snake Nature Photography[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2243″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2244″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2246″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Yuma Proving Grounds, Yuma Co., AZ. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2245″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Photo by Don Swann[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”477″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Sonoran Desert Tortoise, Tucson Mountains. Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

The Sonoran Desert Tortoise is a large (< 322 mm carapace length in Arizona, < 370 mm for the species) terrestrial turtle with a rough, keelless carapace that is gray to orange-brown, the plastron is not hinged, the hind limbs are elephantine, the front feet are shovel-like, and a prominent median projection extends forward from the front of the plastron (gular shield). The digits of the feet are not webbed.  The Ornate Box Turtle is the only other terrestrial turtle in the 100-Mile Circle.  It is smaller (<146 mm carapace length) and the plastron is hinged in the front.

In the 100-Mile Circle, the Sonoran Desert Tortoise is found primarily in Sonoran desertscrub, but also marginally into semi-desert grassland, such as in the Altar and Santa Cruz River valleys south and southwest of Tucson, and the lower San Pedro River Valley to the northeast of Tucson.  But most of the distribution of the species in the Circle and in Arizona lies north and west of Tucson.  Tortoises are occasionally encountered in southeastern Cochise County in an area of Chihuahuan desertscrub and semi-desert grassland, and also along Ruby Road and elsewhere in the Pajarito/Atascosa Mountain range complex in grasslands with scattered oaks and mesquite.  It also likely occurs in foothills thornscrub on the southern edge of the 100-Mile Circle, and occasionally strays upslope into the mountains, even into pine-oak woodland.  But the vast majority of Sonoran Desert Tortoise observations are below 1,280 m elevation in Sonoran desertscrub. The population in southeastern Cochise County may have originated from released Tortoises.  This is a species of mostly rugged terrain – mountains and bajadas, often with boulders or deep arroyos with caliche caves that provide shelters where Tortoises spend the night and escape climatic extremes and predators.  Sonoran Desert Tortoises dig their own burrows, use existing burrows or holes, or improve existing shelter sites.  Although primarily a species of desert mountains and bajadas, the Tortoise occurs in low densities in desert valleys, as well, and presence and movement across such valleys are probably critical for maintaining genetic connectivity and diversity in montane populations.

The Sonoran Desert Tortoise is perhaps the best-studied and most closely-monitored reptile in the 100-Mile Circle. It is diurnal and most active during the summer rainy season (July-early September) and less so in April-June and mid-September to November.  One clutch of 1-12 eggs is laid from early June to early August, although not all females reproduce each year.  Eggs are often buried in the soil of burrows and hatch in September or October; although some may overwinter and hatch in the spring.  Survivorship from egg to adulthood is very low, so larger juveniles and adults must exhibit high survival rates (estimated >94% annually for adults) if populations are to persist.  Large Sonoran Desert Tortoises found in the wild are probably 30 or more years of age, and some may live as long as 60-100 years.

The diet is vegetarian, including a wide variety of herbs, grasses, woody plants, and succulents.  Annual herbaceous plants and grasses are most nutritious when green, but Tortoises eat them when dried as well.  In the late summer and fall when prickly pear cacti are in fruit, it is not unusual to find Sonoran Desert Tortoises with reddish stains around their mouths.

For more than three decades, the Sonoran Desert Tortoise has been the subject of considerable conservation planning and action, much of which was adapted from conservation of the Mojave Desert Tortoise (Gopherus agassizii), a species listed as threatened under the federal Endangered Species Act.  Under Arizona Game and Fish Department regulations, collection of Sonoran Desert Tortoises is illegal without specific authorization.  Threats include habitat degradation, loss, and fragmentation, disease, elevated mortality due to roadkill, illegal collection, and other forms of human-induced elevated mortality or predation.  Release of unwanted pet Tortoises can cause disruption of Tortoise behavior in wild populations, inappropriate genetic mixing, and spread of disease.  The Arizona Interagency Desert Tortoise Team was formed in 1985 to coordinate conservation across agency jurisdictions.  The AIDTT has issued a management plan and standardized mitigation protocols for projects affecting Tortoises and their habitat.  Since 2002, the AIDTT has focused on developing a State Conservation Plan.  More information about the Team can be found at: http://www.azgfd.gov/w_c/desert_tortoise_aidtt.shtml

Sonoran Desert Tortoises are occasionally found in residential areas.  These are likely escaped pets.  Information about what to do if you find such a tortoise, as well as information about tortoise adoption programs, can be found at: http://www.azgfd.gov/w_c/tortoiseencounter.shtml

In 2010, the U.S. Fish and Wildlife Service determined that the Sonoran Desert Tortoise warranted listing as a threatened or endangered species.  Since that time it has been a candidate for listing under the Endangered Species Act.  The Sonoran Desert Tortoise was until recently considered a population or form of the broad–ranging Desert Tortoise (Gopherus agassizii), which as defined now, is restricted to areas north and west of the Colorado River.  Genetic analyses suggest Tortoises from northern Sinaloa and portions of southern Sonora, Mexico are probably a distinct species, as well.

Suggested Reading:

Averill-Murray, R.C., and A. Averill-Murray. 2005. Regional-scale estimation of density and habitat use of the Desert Tortoise (Gopherus agassizii) in Arizona. Journal of Herpetology 39(1):65-72.

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Ernst, C.H., and J.E. Lovich. 2009. Turtles of the United States and Canada (second edition). Johns Hopkins University Press, Baltimore.

Rosen, P.C. (ed.). 2014. Conservation status, ecology, and distribution of Desert Tortoises in Mexico. Report to United States Fish and Wildlife Service, Arizona Ecological Service Office for Science Support Program Grant GX11BD30EH81500.

U.S. Fish and Wildlife Service. 2010. Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Sonoran Population of the Desert Tortoise as Endangered or Threatened; Proposed Rule.  Federal Register 75(239):78094-78146.

Van Devender, T.R. (editor). 2002. The Sonoran Desert Tortoise Natural History, Biology, and Conservation.  University of Arizona Press and the Arizona-Sonora Desert Museum Press, Tucson.

Zylstra, E.R., and R.J. Steidl. 2009.  Habitat use by Sonoran Desert Tortoises. Journal of Wildlife Management 73(5)747-754.

Author: Jim Rorabaugh

For additional information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 1988-91 Collected Papers:87-88, 175-178; 1993 Mar:27-28; 1993 Apr:40-42; 1996 Apr:31-35; 1996 Nov:116-118; 1999 Jul: 70-72; 2000 Sep:98-102; 2001 Dec:131-137; 2002 Jul:78-79; 2003 Jan:6-7; 2004 May:50-53; 2005 Mar:30-31; 2007 Jul:73; 2007 Aug:86; 2007 Sep:97; 2008 Jun:62-65; 2008 Aug:86-89; 2008 Nov:124; 2008 Dec:136; 2009 Sep:98-100; 2010 Aug:115; 2010 Nov:155; 2011 Jan:4-5; 2011 Jul:71-72; 2011 Oct:106-107; 2012 Jan:4-6; 2013 Dec:85-89; 2014 Dec: 91-95, 2015 Mar:10-11; 2016 Dec:60-63.

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