Free-ranging dogs attack and kill threatened desert tortoises – Image for illustrative purposes only (Image credits: Unsplash)
In the arid stretches of eastern California near Daggett, a routine tracking effort turned into a stark discovery. A young male Agassiz’s desert tortoise, previously healthy, was found severely injured after an encounter with free-ranging dogs. The animal later died from its wounds, adding to a pattern that researchers have documented over many years.
A Persistent and Expanding Risk
Wildlife biologist Kristin Berry of the U.S. Geological Survey has tracked threats to these tortoises for decades. Her work revealed that dogs allowed to roam freely, whether owned pets or feral animals, have contributed to hundreds of attacks across the Colorado and Mojave deserts. The findings come from a study published in Wildlife Monographs that examined three decades of data.
These reptiles already face habitat loss from urbanization, off-road vehicles, and grazing. Predation by coyotes and ravens adds further pressure. Dog attacks represent an additional, often overlooked danger that has grown as human settlements push deeper into tortoise habitat.
Evidence Gathered Through Careful Analysis
Direct observation of attacks proved difficult, so researchers relied on detailed examination of thousands of tortoises. They reviewed photographs of 6,727 individuals collected between 1977 and 2006 at 50 sites. Signs of severe trauma to shells, limbs, and gular horns appeared in more than 15 percent of the animals.
Nearly 4.5 percent showed damage to the gular horns, which dogs often chew while the tortoise retreats into its shell. Some tortoises survived one attack only to suffer a second. Females and older individuals proved especially vulnerable. Most affected tortoises were found within 12 kilometers of human settlements, with risk and injury severity increasing closer to towns.
Why Settlements Fuel the Problem
Many dogs involved belong to owners who allow them to wander. Others form packs far from any house. Contractors working on tortoise surveys have reported being chased by groups of dogs, sometimes forcing them to seek safety in vehicles. Hikers who let pets off leash have also documented attacks on tortoises.
As neighborhoods expand into desert areas, the overlap between dogs and tortoises increases. The proportion of tortoises showing attack injuries has risen over time. Berry noted that many California populations are no longer viable, with adult females declining faster than males. In 2025 the California Fish and Game Commission listed the species as endangered in the state.
Practical Steps That Could Make a Difference
Simple barriers offer one promising approach. Higher fences around new developments can limit how far dogs range into critical habitat. The Red Cliffs Desert Reserve in Utah already requires such measures for new homes along with leash rules, though enforcement remains challenging.
Berry emphasized that modest fencing can produce noticeable results in some locations. Coordinated efforts between land managers, local governments, and residents will be essential as development continues. Without action, the pressure on remaining tortoise populations is likely to grow.
What matters now: Free-ranging dogs represent a manageable but growing threat that requires attention from both conservation agencies and desert visitors.
The pattern documented by Berry and her colleagues shows that everyday choices about pet management can directly affect the survival of a threatened species. Continued monitoring and targeted protections remain necessary to give these slow-moving desert residents a better chance.
