Plants, insects, and larger animals, like the forest’s white-faced capuchin monkeys, are well adapted to these changes. But in 2015, during an abnormally severe drought influenced by the El Niño–Southern Oscillation (ENSO), Perry, an evolutionary anthropologist at the University of California, Los Angeles, observed behaviors that once seemed impossible.

Under normal conditions "The [capuchin] mothers are quite devoted," she explained. "Now, I was seeing babies crying on the ground piteously. And the mothers just looking down like 'Too much trouble' and walking off, abandoning their infants."