Are tortoises starving to death in Joshua Tree?

The corpses of apparently starved and dehydrated tortoises are littering part of Joshua Tree National Park, and the culprit may be climate change.

In 1978, researcher John Barrow began surveying Agassiz’s desert tortoises in a one-square-mile patch of the park in the Sonoran Desert, California. During that year, Barrow marked any tortoises he found by notching their shells with a metal file. Other researchers continued the work in the 1990s and early 2000s, marking the animals with epoxy tags or yellow or green paint.

The authors of the current study returned to the site in 2012 and conducted 14 surveys of the plot. They searched for tortoises and investigated burrows with flashlights and sticks. The team also collected coyote scat to find out if these predators had eaten tortoises.

The researchers found 14 living and 64 dead tortoises, they report in Biological Conservation. About 30 percent of the deaths probably occurred since 2008. “The postures and positions of a majority of dead tortoises found in 2012 were consistent with death by dehydration and starvation,” the team writes.

The estimated number of tortoises also dropped from about 200 to less than 50 between 1996 and 2012. Many of the carcasses had been picked over by other animals; some tortoises were missing their heads or limbs, and four coyote scat samples contained tortoise remains.

The authors speculate that longer, more frequent droughts may have hastened the tortoises’ deaths. The dry weather might also have caused small mammals, such as rabbits, to reproduce less. Faced with a food shortage, predators that normally eat rabbits might have then attacked tortoises instead. Roberta Kwok | 17 December 2013

Source: Lovich, J.E. et al. 2013. Climatic variation and tortoise survival: Has a desert species met its match? Biological Conservation doi: 10.1016/j.biocon.2013.09.027.

Image © Ryan M. Bolton | Shutterstock