In 2017, during the bird kill, most of the colony on East Sand Island fled, in an event the Audubon Society called a "catastrophic collapse" of the largest population of double-crested cormorants in the world. The corps says there's no direct evidence to link the two events. But the mass exodus came during the corps' third year of shooting thousands of birds out of the air, destroying their nests and setting off explosives on the island.