The thumb-sized ecosystem engineer just got a third home

The Pacific pocket mouse — as long as a human thumb, weighing six to seven grams — is one of North America's smallest and most endangered mammals. Twenty years after the San Diego Zoo Wildlife Alliance began its recovery program, a third reintroduced population is now established at Camp Pendleton. More than 500 mice have been released into new and existing populations, digging burrows that improve the soil and shelter other species.