The Sonoran Desert spans 310,000 km² across Arizona, California, and Mexico's Sonora and Baja California. It is North America's hottest and most biologically diverse desert — home to saguaro forests, extraordinary reptile diversity, and species found nowhere else. Climate change is intensifying heat that challenges wildlife thermal tolerance.
Wildlife biologists have documented mule deer injured attempting to cross wall structures and pronghorn behavior disruption near wall sections. The Defenders of Wildlife and Center for Biological Diversity have litigated for wildlife passage accommodations in wall design.
After being eliminated from the US by the 1960s, jaguars are gradually recolonizing Arizona from Mexico. As of 2025, 6-8 individual males have been documented in the Sky Islands of southern Arizona. Each individual is precious for population recovery. Welfare concerns include: vehicle strikes on highways, conflict with ranchers who fear livestock depredation, and the border wall reducing connectivity with the larger Mexican jaguar population these animals are attempting to connect with.
Fewer than 160 Sonoran pronghorn survive on the Arizona-Sonora border — the rarest large land mammal in North America. Their welfare is critically dependent on: water availability (they can die of thirst in days during extreme heat); food quality; and the ability to move between US and Mexican habitat. A captive breeding program at Cabeza Prieta National Wildlife Refuge maintains insurance animals. Drought years see pronghorn mortality from dehydration — monitoring programs provide emergency water.
The Sonoran Desert's reptile diversity is extraordinary. Welfare challenges include: illegal collection for the pet trade (regal horned lizard, Gila monster); vehicle strikes on desert roads at night (when reptiles thermoregulate on warm asphalt); and increasing temperatures reducing thermal safety margins. Gila monsters face collection pressure; some populations near urban areas are significantly depleted.
The Sonoran Desert is warming faster than the global average. For ectothermic reptiles, rising temperatures reduce "operative temperature range" — the number of hours per day when temperatures are safe for activity. Models project that some Sonoran Desert lizard species will face activity restriction exceeding 50% by 2080 under high-emissions scenarios, with energy budget and reproductive welfare impacts.
Desert water provisioning for wildlife — maintained by government agencies and volunteer groups throughout the Sonoran Desert — represents a direct welfare intervention saving thousands of animals during extreme heat events. The Tucson Audubon Society, Sky Island Alliance, and Arizona Game and Fish Department coordinate water "charco" (pond) maintenance.