Toni Pirkl, Jamestown (N.D.) Sun, Published June 22 2009
Pelican numbers down at Chase LakeEverything appears to be normal in the colony of American white pelicans nesting at Chase Lake, but for some reason the numbers are the lowest in 17 years.
As counted the first week in June, nests on the Chase Lake National Wildlife Refuge’s three islands number 7,236. That means there are 14,472 breeding pelicans there, down significantly from the 17,302 nests or 34,604 breeding pelicans in 2006.
“That’s the lowest number since 1992,” said Paulette Scherr, wildlife biologist for the U.S. Fish and Wildlife Service. “We can’t really explain why the numbers are lower. But they look healthy and everything looks normal.”
White pelicans have been spending summers nesting and bringing up their young at Chase Lake for more than a century. Numbers in the colony have always varied, with a recorded low of 5,000 nests in 1972 to an all-time high in 2000 of 17,733 nests.
“Generally from 1972 until the mid-1990s the nests were in the 4,000 to 8,000 range,” Scherr said. “But since the drought broke in 1993, the numbers started going up.”
Food sources might have been a reason for low production during the 20 years starting in 1972. Scherr said the wetlands were dry during that period and lake levels were down. It’s difficult to pin down the reason because pelicans can fly as far as 100 miles in search of food.
However, the wet years brought a rising population of pelicans to Chase Lake to nest. In 1997, the nests numbered 9,000 and then 12,000 in 1998. Pelicans nest in pairs so one “baby-sits” while the other is hunting food. The number of breeding pelicans peaked at 35,466 in 2000, making Chase Lake the largest colony in North America.
Then in 2004, within a few weeks of their arrival, the Chase Lake pelicans abandoned their nests and disappeared, leaving behind eggs and young. Several theories were floated as to what happened, but none has proved conclusive. And although they came back in 2005, West Nile Disease that summer took a heavy toll on the featherless young birds, which are susceptible to the mosquito-borne illness. Scherr said West Nile is an annual problem, but it doesn’t usually surface until July.
Scherr said colonizing birds like the pelicans are susceptible to a variety of diseases. In 1992, for example, there was a die-off of white pelicans at Chase Lake from disease but the exact cause was never determined.
“We think it’s Mother Nature’s way to keep the population in check,” she said. “And since 2002, we’ve only had one good production year.”
What could also be influencing fluctuations in production, Scherr said, is the weather. Around 20 years ago, the white pelicans began returning to nest about two weeks earlier in the spring. That meant eggs hatched sooner and the infant and young birds were subjected to vagaries in the spring weather, which can produce very cold rains or snow, hail and low temperatures. This year, for the first time, the pelicans returned two weeks later and that helped.
Little is actually known about white pelicans. Until they abandoned their nests in 2004, the pelicans were just one of hundreds of bird species migrating through the Arrowwood National Wildlife Refuge Complex. However, since their disappearance, the USGS Northern Prairie Wildlife Research Center and the Fish and Wildlife Service have received funding to study the pelicans. This year, Scherr said, the service has hired a technician to monitor the pelican nesting site.
“We’ll be keeping better tabs on the pelicans so if anything does happen, hopefully we’ll know,” she said.
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