Wildlife officials at a North Dakota refuge have a mystery on their hands: Why did 27,000 pelicans suddenly abandon their nests and more than 100,000 eggs? And where have the birds gone?
“What is perplexing is that they have nested out there for so many years and nothing like this has occurred. And that is another twist in the mystery, why all of a sudden did they leave this year?” said Mick Erickson, manager of the Chase Lake National Wildlife Refuge, the largest nesting ground of the American white pelican.
An entire colony on a peninsula of the lakeshore and a colony on an island in the lake vanished over the course of a few days in May and the first week of June. The third and last colony, numbering 2,500 pelicans on another island, is all that remains.
The refuge was established in 1908 and fewer than 50 pelicans nested there in the early 1900s. By 2000, a record-high 35,000 birds made the refuge their summer nesting grounds on more than a dozen acres.
There are several theories as to why the colonies suddenly dispersed. Human activity on the mainland may have frightened the birds away, but that does not explain why the secluded island colony also took flight.
Predators could have become too dangerous and could have been swimming out to the island. The threat of disease also may have driven the birds away.
“Whether too many humans were going out there and taking photos or there could be a number of predators, coyotes that maybe frequented the colony every night and harassed them, that would cause enough of a disturbance for them to leave,” Mr. Erickson said. “We’re concerned about next year. We hope they come back and are pretty confident. But the long-term effect of this [is], we won’t know for two or three years down the road.”
The disappearance of the island colony has wildlife officials “scratching our heads,” he said. “This is the first time we know of where just a large mass of pelicans have abandoned their nests.”
Diseases claimed 4,000 young birds last year. Wildlife officials are monitoring whether cholera, botulism, or West Nile virus is the culprit.
“Like a head cold, [disease] travels fast, and that might be something else going on in the colony — a nonfatal disease may be causing them to leave,” Mr. Erickson said.
On the third colony, the young have hatched and appear healthy.
Officials have alerted other wildlife refuges across the Midwest to be on the lookout, but there have been no reports of a sudden emergence of white pelicans. Mr. Erickson suspects that the pelicans may have resettled in the “prairie pothole region,” a series of rolling hills and wetlands that dot the state’s landscape.
“They may be scattered out through thousands of miles of potholes eating and loafing, and that might be why we have not picked up reports,” he said.
As for the eggs left behind, Mr. Erickson said “the damage is already done.” Without incubation, the embryos never had a chance to develop fully.