Chaco tortoise  (Geochelone chilensis)

This tortoise's common name is taken from the Chaco regions of Argentina and Paraguay in which it lives, but the Latin name chilensis is misleading, since the species is not native to Chile (4). The oval upper shell (carapace) may be either totally yellowish brown or have dark-brown to black growth rings (annuli) surrounding a tan centre on each scute. The rim of the shell is slightly serrated and has a dark wedge of pigment at the back edge of each scute. The lower shell (plastron) may be uniformly yellowish-brown or have a dark triangular wedge along the seams of each scute. The head, limbs and tail are greyish to yellowish-brown, with the front of each forelimb covered with large, angular scales and each thigh featuring several enlarged tubercles (2).

Native to Argentina and Paraguay, from the Bolivian border into western Paraguay and north-western Argentina (1) (2).

Occurs in dry, sub-montane plains, deserts and semi-deserts with scrub and trees, from below sea-level to over 1,000 m (2).

Most activity occurs in spring, particularly during the mornings, when the Chaco tortoise feeds primarily on plants of the Plantago genus. In summer, the diet comprises grasses, succulents and fruits of perennial shrubs. In northern Patagonia, at the beginning of each spring the Chaco tortoise digs short burrows (50 – 60 cm) in sandy soils, in which it seeks refuge at night and during the mid-day heat. Dens are also constructed, but these are much deeper (usually over 2 m), dug in hard soil and used over several seasons. In the southernmost part of its range, this species has been reported to hibernate for as long as five months in burrows or dens (2).

Mating occurs during November and December, and nesting from January to March. During the breeding season, males aggressively defend their territories from rivals, biting their enemy on the forelimbs, sometimes inflicting bleeding wounds (2) (5). Up to three clutches of one to seven eggs may be laid each season, which hatch after 12 to 16 months. Sexual maturity is thought to be reached at 12 years (2).

The Chaco tortoise is collected from the wild and exploited for the pet trade and sometimes for food (2) (6). Juveniles have been captured and sold domestically as pets since the 1950s, but it was not until the 1980s that international demand began to grow, as trade in other tortoise species became progressively banned (6). Despite protection by national and provincial laws, 20,000 to 50,000 of these tortoises are estimated to be collected annually in Argentina for the domestic pet trade, mainly from the provinces of Córdoba and Santiago del Estero (2) (6). Additional threats include free-ranging livestock, which compete for food and trample both vegetation and tortoise burrows. Local burning practices may also impact populations by directly injuring or killing the tortoises, particularly juveniles, as well as reducing the overall diversity of plant foods available to the species (2). Like many other tortoises, the Chaco tortoise has a late onset of maturity and low reproductive rate, making diminished populations slow to recover (5).

The Chaco tortoise is listed on Appendix II of CITES, limiting and regulating its international trade (3).

For more information on this and other tortoises see:

• Turtles of the World (CD-ROM), by Ernst, C.H., Altenburg, R.G.M. and Barbour, R.W.
  http://nlbif.eti.uva.nl/bis/turtles.php?menuentry=inleiding

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