To track the tortoises and study their habits, biologists attach small VHF transmitters and GPS data loggers to the shell of each tortoise they find. They also paint a unique number on the tortoise’s shell, and file a small notch through one of the keratin scutes at the thin rear edge of the shell, which has a consistency similar to a human fingernail. All this is done after an examination of the tortoise’s health and weight.

Coaxing one of the creatures out of their shelters can be a challenge: if they feel threatened, they oftentimes wedge themselves against the rear wall and ceiling of their miniature caves, which can be yards deep.

“They’re shockingly strong,” said Hillary Hoffman, a herpetologist with the Arizona Game and Fish Department who has been coming to YPG since 2009. “If they don’t want to come out, they’re not coming out.”