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Sonoran Desert Tortoise

The Sonoran desert tortoise is native to the Sonoran deserts of Arizona and northwestern Mexico. In the U.S., it is distributed in western, northwestern, and southern Arizona. In Pima County, the desert tortoise is found in many areas below approximately 4,200 feet in elevation, where it prefers rocky hillslopes and washes. It generally avoids wide, flat valley bottoms unless there are deeply incised washes.
desert tortoise The desert tortoise can live up to 80 years; it grows slowly and generally has a low reproductive rate. It spends most of its time in burrows, rock shelters, and pallets to regulate body temperature and reduce water loss. It is most active after seasonal rains and is inactive during most of the year. This inactivity helps reduce water loss during hot periods, whereas winter hibernation facilitates survival during freezing temperatures and low food availability.

 The desert tortoise is key monitoring element of the Pima County MSCP; no other species will receive as much effort over the 30 years of the permit.  Pima County agreed to monitor at least 10 sites, but a key first question was: where do they occur? After the MSCP was signed in 2016, County staff began a thorough assessment of County open-space properties to determine the distribution and relative abundance of tortoise. In the process, we found a number of previously unknown populations, especially in the in San Pedro River Valley.

Desert tortoise chollaAfter considerable discussion of tradeoffs and consultation with species experts, County staff determined the most prudent approach would be to focus our efforts on the County properties that make up the Tucson Mountains, most especially Tucson Mountain Park, but also Sweetwater Preserve, and Painted Hills.  Monitoring in the Tucson Mountains began after the start of the monsoons in early July 2018 and concluded in late September.  We established 20 long-term monitoring sites, visiting each 3 times during the summer.  In all, we observed and marked 44 tortoises with each barring a white “license plate” number for future identification.  We plan to repeat this monitoring effort in 2020 or 2021.   As of October 2018, we are still analyzing data from the effort, in general we are thrilled with the results we obtained, most importantly that the Tucson Mountains hosts a robust population of tortoises.  While our one-year effort is among the most significant monitoring efforts for this species in the mountain range, the County’s unprecedented commitment to monitoring this species will provide one of the most significant monitoring efforts for the species anywhere in its range.

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Conservation Science

201 N. Stone Ave., 6th FL
Tucson, AZ 85701

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