}

The San Bernardino National Wildlife Refuge is one of the largest natural wetlands in the Southwest and a crucial protected area along the U.S. border.

According to the U.S. Fish and Wildlife Service, the refuge is “an important link for wildlife to migrate between Mexico’s Sierra Madre Occidental and the Rocky Mountains to the north.”

That path soon will have a 30-foot-tall barrier blocking it, with steel bars spaced four inches apart. Smaller species will be able to fit through the gaps, but larger mammals will no longer be able to reach habitats on both sides.

Construction crews have left gaps in the barrier where dry washes and creek beds cross into Mexico because those areas will need specialized fencing with liftable storm gates to allow water and debris through.

For now, they are the last few places where large animals can still cross the border.

Working with the Phoenix Zoo, Myles Traphagen, whose group, Wildlands Network, works to protect migration corridors for North American species, set up motion-sensor cameras in January along two of these creek channels, Hay Hollow Wash and Black Draw. The group opposes the border wall project.

Here are some of the species he captured crisscrossing the U.S.-Mexico border:

Advocates for these animals also are concerned because the Mexican highway that runs south of the border is being expanded from two lanes to four, making it potentially more lethal to wildlife. If an animal migrating north manages to safely cross the roadway, it will hit the new border barrier and have to turn back, needing to cross four lanes of traffic again.

“This border wall is going to be a killing machine,” Traphagen said.

Read More