When biologist Luis Zambrano began his career in the late 1990s, he pictured himself working miles from civilization, maybe discovering new species in some hidden corner of Mexico’s Yucatán Peninsula. Instead, in 2003, he found himself counting amphibians in the polluted, murky canals of Mexico City’s Xochimilco district. The job had its advantages: he was working minutes from his home and studying the axolotl (Ambystoma mexicanum), a national icon in Mexico and arguably the world’s most recognizable salamander. But in that first year, Zambrano couldn’t wait for it to be over.
“Let me tell you, I hated the project at the beginning,” he says. For one thing, “I couldn’t catch anything”.Over time, however, he did catch some axolotls. What he found surprised him—and changed the course of his career. In 1998, the first robust study to count axolotls estimated that there were about 6,000 of them per square kilometre in Xochimilco. Zambrano—who now is a professor at the National Autonomous University of Mexico (UNAM) in Mexico City—discovered in 2000 that the number had dropped to about 1,000 animals per square kilometre. By 2008, it was down to 100; today, thanks to pollution and invasive predators, there are fewer than 35 animals per square kilometre.