Young bolson tortoise at the El Paso Zoo, Photo by Rick LoBello

Bolson Tortoises are endemic to the Chihuahuan Desert

Here in the Chihuahuan Desert we have many endemic species. For those not familiar with that term, biologists use the word "endemic" for plant and animal species growing or existing only in a certain place or region.  Biologists estimate that there are 156 reptile species in the Chihuahuan Desert with 24 species of endemics. One of those endemics is the bolson tortoise, also known by the names Mexican giant tortoise and yellow-bordered tortoise. In Mexico it is called tortuga grande, tortuga llanero or tortuga topo.

Bolson tortoises once lived in the El Paso area thousands of years ago. They are the largest tortoises in North America reaching 18" in length and weighing up to 30 pounds.  The species was discovered by accident very recently in 1959.   

Over 12,800 years ago they disappeared over a large portion of their range at the close of the Pleistocene. Today they survive mainly in one small area of northern Mexico near Torreón, Coahuila.  I first came to know this species during the spring of 1990 when I was working as Executive Director of the Big Bend Natural History Association. Park Superintendent Jim Carrico, Chief Ranger Phil Koepp and I joined officials from Texas Parks and Wildlife Department on a trip to visit critical bolson tortoise habitat in Mexico.  We were joined by scientists from California who were studying the bolson tortoise at the Bolsón de Mapimí Man and the Biosphere Reserve and Research Station in Durango.  Soon after we returned the Los Angeles Times published a story about a proposed reintroduction effort that would return bolson tortoises to their former Pleistocene range in Big Bend National Park. Twenty-four years later there is no serious effort to return this species to the park, but the effort remains on the radar screen of Big Bend park officials with the help of the Turner Species Endangered Species Fund.

At the El Paso Zoo there are two enclosures for bolson tortoises in the America Lands area and adjacent to the main entrance to the El Paso Water Utilities Discovery Education Center. During the winter months from about October to February bolson tortoises hibernate in underground burrows. As a result don't expect to see them at the Zoo until sometime in March or April.

The El Paso Zoo is working with the Turner Endangered Species Fund and the Living Desert Zoo and Gardens State Park in New Mexico to help with a reintroduction effort. Zoo staff are assisting research scientists in determining the gender of baby tortoises, as part of a larger effort to breed bolson tortoises for eventual release into portions of their former range.

According to the IUCN Red List "this species is listed as Vulnerable because it has experienced a population decline of up to 50% over the past 3 generations. It faced catastrophic levels of exploitation during the middle of the 20th century, with subsequent lower levels of exploitation. At present the species is protected from direct exploitation and part of its extent of occurrence is protected, but some subsistence collection and habitat degradation impacts likely still occur. With the worst impacts over, it is rated Vulnerable (under A1) rather than Endangered (under A2). About six separate subpopulations exist, comprising some 7,000 to 10,000 adults, collectively occurring over about 7,000 sq. km."