By JAMES MacPHERSON
2014-06-28 11:42 PM
BISMARCK, North Dakota (AP) -- Rising lake levels are swallowing American white pelicans' nesting grounds at a guano-rich island in North Dakota known as North America's largest refuge for the big-billed birds, U.S. federal wildlife officials said.
About 30,000 pelicans returned to 4,385-acre (1,774-hectare) Chase Lake National Wildlife Refuge this year to find water had gobbled several acres of their main nesting island, creating increasingly cramped conditions for the giant birds, among the largest in North America. They weigh up to 20 pounds (9 kilograms), have a wingspan of nearly 10 feet (3 meters) and measure six feet (1.8 meters) from bill to tail.
The decreased room does not appear to have affected nesting activity so far, and the island continues to be filled with the grunts and squawks of thousands of white pelicans and their chicks, said Neil Shook, a U.S Fish and Wildlife Service biologist and refuge manager.
The first chicks hatch around mid-May, a month after their parents fly in from Gulf Coast states and as far away as Florida and California. The pelicans normally stay through September, feasting on fish and salamanders from small ponds within a 100-mile (161-kilometer) radius of the refuge.
Shook said the island has been shrinking by a couple of acres (nearly one hectare) annually since the early 1990s but appears to have mysteriously decreased from 24 acres (10 hectares) last year to about 15 acres (6 hectares) this year. The decrease of island real estate comes despite relatively average rain and snowfall -- and it has even shrunk in dry years, he said. It's not clear why it's happening.
"As the water level at Chase Lake continues to rise, we're losing a little of the nesting island each year," Shook said.
Chase Lake historically has had high alkaline levels that made it unable to support aquatic life, but Shook said that's changing as the lake level increases.
"The lake is changing and becoming more of a freshwater lake even to the point that it now has a few minnows and salamanders but not enough for the pelicans to feed on," he said. "I don't think change in water chemistry is enough to make the birds leave but loosing nesting habit -- that could be an issue."
Biologists aren't overly worried yet. The main nesting island was first used by pelicans in early 1990s after an island previously preferred by the pelicans was swamped by rising lake water. But other islands over the decades have cropped up when parts of peninsulas are flooded, he said.
Pelicans have been monitored at Chase Lake since 1905, when the birds numbered about 50. President Theodore Roosevelt designated the site as a bird refuge in 1908, after many were being killed for their feathers and for target practice.
Biologists have been doing aerial surveys since 1972. But the pelican rookery has presented puzzling situations for biologists before.
In 2004, nearly 30,000 pelicans departed the Chase Lake refuge, leaving their chicks and eggs behind. A year later, the refuge saw a massive die-off of pelican chicks, followed by an exodus of their parents.
Predators, weather, diseases and other factors were considered but biologists have never pinpointed the cause of the pelican deaths and departures. Shook said that it may have just been a natural correction.
Since that scare, the nesting population has been on the rise.