Gopherus Agassizii (Desert Tortoise). Mortality

We report the death of a tortoise apparently caused by red brome grass (Bromus rubens). During 1989-1995, we monitored 276 tortoises in the northern Mojave Desert using radiotelemetry at Yucca Mountain, Nevada (36.85°N, 116.43°W). Among these tortoises, we observed about 30 individuals (but none of 72 hatchlings < 3 months old) with compact masses of B. rubens seeds (i.e., florets) and stems in their femoral pits (the pits formed anterior to the femur when tortoises retract their hind legs). The masses generally were not readily visible during routine monitoring, and smaller masses could have been overlooked when tortoises withdrew into their shells. However, several of the masses were large enough to prevent the animals from fully retracting their hind limbs into the shell.

We found one dead tortoise (carapace length [CL], = 57 mm) in 1993 with compact masses of B. rubens in its femoral pits. We necropsied the animal and found that the vegetation had abraded and penetrated the skin and muscle of the femoral pits, entered the coelomic space, and apparently caused substantial necrosis of the mesentery and muscle. We observed no other indications of cause of death. In late 1995, we recorded another case in which a mass of seeds had abraded the skin in the femoral pits, and about 20 seeds had become embedded in scab-like material. We generally removed the B. rubens during routine handling.

We also recorded three cases in which a tortoise had a B. rubens seed in its eye (presumably under the eyelid). For two of these tortoises (CLs = 141, 247), the seed was removed and there was no apparent effect (e.g., loss of the eye or apparent blindness) during 2 yr of additional monitoring. In the third case (CL = 248), removal of the seed was not noted, but there was no apparent effect during 3 yr of additional monitoring. In another case, a tortoise (CL = 248) was found with one B. rubens seed in each nostril; these were removed, and there was no apparent effect during 2.5 yr of additional monitoring. In a different study conducted during 1998, a tortoise (CL = 213) was found near Barstow, California, with a Bromus seed in one eye (T. Gardner, Utah State University, pers. comm.). Both eyes were inflamed and tightly shut. After the seed was removed and the eyes were washed, the animal’s vision appeared unaffected.

Because vegetation in the shell openings was difficult to see unless the femoral pits were specifically examined (which was not done during every observation in our study), and because desert tortoises have no apparent mechanism for removing these masses of vegetation, this situation may be more common than we note. We encourage other researchers to carefully inspect tortoises so that the frequency at which masses of vegetation occur in femoral pits can be estimated.

Originally authored by: James L. Boone¹,², Danny L. Rakestraw¹, Elizabeth A. LaRue², and Kurt R. Rautenstrauch¹, Science Applications International Corporation (SAIC)¹, 1211 Town Center Dr., Las Vegas, Nevada 89134, U.S.A., and Nevada State Museum², 700 Twin Lakes Drive, Las Vegas, NV 89107 U.S.A.

Tortoises were handled under permits PRT-683011 and PRT-781234 from the U.S. Fish and Wildlife Service, and S-0446, S-1595, S-3108, S-5041, S-6941, and S-9060 from the Nevada Division of Wildlife. This research was supported and managed by the U.S. Department of Energy, Yucca Mountain Site Characterization Office, as part of the Civilian Radioactive Waste Management Program under contracts DE-AC08-88NV1067, DE-AC08-93NV11267, DE-ACO1-91RW00134, and DE-ACO8-91RW00134.

Acknowledgments. Data used in this manuscript were collected during monitoring supported and managed by the U.S. Department of Energy, Yucca Mountain Site Characterization Office, as part of the Civilian Radioactive Waste Management Program under contracts DE-AC08-88NV10617, DE-AC08-93NV11265, DE-ACO1-91-RW-00134, and DE-ACO8-91-RW-00134. We appreciate the efforts of the reviewers who helped improve earlier drafts. Tortoises were handled under permits PRT-683011 and PRT-781234 from the U.S. Fish and Wildlife Service, and S-0446, S-1595, S-3108, S-5041, S-6941, and S-9060 from the Nevada Division of Wildlife.