QUOTE : On October 7 the cormorants abruptly came back, hundreds of thousands of them, only to disappear after a week. On the 20th the birds returned, then vanished on the 24th. By November 7 they were back—only to bolt a few days later. In 1940 the warm waters came again. And in 1941. And they showed up earlier, at the beginning of nesting, so the birds then fled their nesting grounds and didn’t reproduce. Entire generations were not being born. Vogt was looking at a demographic collapse. But why were the Guanays fleeing? The temperature was not enough to hurt them directly; if they got hot, they could always take a swim. Nor did the birds’ returns correlate with colder weather. They suffered from no obvious disease. What was going on? The key to the puzzle, Vogt thought, was the condition of the few adults that didn’t leave the Chinchas: hungry. The remaining Guanays left every morning to hunt for fish. But they returned ever later in the day, and their crops were often empty, which meant they couldn’t feed their offspring. The lack of food, he concluded, was due to El Niño. Warmer water on the surface acted as a cap that blocked cold water from rising from the depths of the Humboldt Current, which set off a cascade of horribles: no upwelling meant no nutrients for plankton, which meant no plankton for anchovetas, which meant no anchovetas for Guanays.