PETCHABURI, Thailand — Swaths of butterflies flutter around Chalong Thongsong and his team of rangers and researchers as they walk along a muddy trail into the forest of Kaeng Krachan National Park. The biggest of Thailand’s national parks, Kaeng Krachan is home to more than 450 wild animal species. Arriving at a camera trap chained to a tree, the rangers work quickly: one unlocks the camera cage and removes the memory card, which another plugs into a laptop. A civet, a pack of dholes, and even a family of elephants appear on the screen. At the third camera-trap site, they find what they’re looking for. Gathered around the laptop, they watch, mesmerized, as a leopard strolls along the very footpath they’re now standing on. “We estimate that, within the 1,000-square-kilometer [nearly 400-sq

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