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They’ve been on the endangered species list since the 1990s, and now the desert tortoise is facing new challenges.

The 10-inch, 12-pound reptile is the Mojave’s most iconic animal, but the desert tortoise is on the brink of extinction, and it turns out humans are one of their biggest threats.

Michael Vamstad has worked at Joshua Tree National Park for 18 years.

The wildlife ecologist regularly travels along the desert scenery to look for tortoises being tracked in the park. On this day, within 30 minutes of carefully trekking through the desert, he finds Elizabeth, a female tortoise who is around 40 years old.

A small radio transmitter affixed to her shell sends a signal to his receiver.

“Every time we find a tortoise we take GPS points using our tablet,” Vamstad said.

There are currently 12 tortoises being monitored by the National Parks Service. They’re all checked on about every two weeks during the active season.

California first listed the desert tortoise as ‘threatened’ under the state’s Endangered Species Act in the late 1980s. They joined the federal list in the 1990s and since then, their population has declined by nearly 90%.

“We’ve done surveys for desert tortoise in the late ’80s, early ’90s, within the park, and found that there is close to 20 to 30 tortoises per square kilometer.,” Vamstad said. These days, there are less than four turtles per square kilometer, and last year, the number dipped to 3.2 tortoises per square kilometer.

“Why the three is very important is that anything under three tortoises per square kilometer actually puts the species at risk of extinction,” Vamstad said.

Why the massive decline? Vamstad says there are several reasons including drought, disease, and … traffic collisions.

“Likely the biggest threat to our desert tortoises in the park are people hitting them with their cars,” he said.

Last year, the park saw 3 million visitors for the first time, so park officials put up signs warning drivers to be on the lookout for the endangered reptiles. There’s even a video on their website showing how to move one off the road correctly.

In addition to unexpected human interactions, desert tortoises are also having a hard time dealing with California’s worsening drought.

The desert tortoise can store water for up to a year, and although their name suggests they belong in an arid environment without much water, they aren’t doing well living in severe drought.

“They can handle certain amount of drought but it seems like we are getting more and more droughts back to back and it’s knocking them down,” Vamstad said.

Disease also put a dent in the tortoise population in the late 1990s.

One prevalent disease is caused by a bacterium that gives them symptoms similar to a common head cold.

“If you’re a tortoise living in the desert like this and you get a head cold, you’re going to lose a lot of water and that tends to be why it kills them,” Vamstad said. “They’re already under water stress.”

The disease is still going around but not as much as 15 years ago, when wildlife experts would often see tortoises with runny noses.

Although most of us will never see their impact, Vamstad said their survival is crucial to the ecosystem.