Last spring, 30,000 American White Pelicans migrated north to their traditional breeding grounds at Chase Lake National Wildlife Refuge in North Dakota, as they have done for decades. There, they went about the usual spring business of creating the largest pelican rookery in North America, a vast sociable colony for the purpose of nesting. Then, for some inexplicable reason, they all left. The abandoned eggs remained in the nests, exposed and vulnerable to prey. No one knows why. Biologists studied the Chase Lake environment for signs of virus, bacteria, or other natural phenomena that could have driven the adults away, but came up empty-handed.

This spring, the pelicans came back, all 30,000 of them. They began nesting and laying eggs again, and to everyone’s relief, things seemed to have returned to normal.

But then the eggs began to hatch -- and the chicks began to die. Over 8,000 baby pelicans died. Some time in late May, the parents abandoned the rookery. Unhatched eggs were simply left behind.

Is it coyotes? West Nile Virus? In either of these cases, adult carcasses would have been found alongside the young; but they were not. The adults were not sick or harmed. They just left. Global warming or other climate change? Not enough food? No one knows.

The adult pelicans have been seen in nearby states, loafing on lakes and feeding. GPS chips had been attached to four of the adults before they left Chase Lake; after it was discovered they were gone, scientists tracked them and found that they all went off in different directions, showing no pattern to their geographic choices, but suggesting that some stressor came along suddenly and the birds all just lifted off and went their separate ways.