Patrick Springer, Published January 26 2014
A pelican problem
Pelicans are flocking to Chase Lake from their southern winter havens about two weeks earlier than before, and the early migration can be deadly for young chicks.
The earlier migration, occurring an average of 16 days sooner than in 1965, is attributed by scientists to the earlier onset of warm weather along the Gulf Coast and surrounding areas, where the pelicans spend their winters.
“Something’s prompting them to migrate earlier,” said Marsha Sovada, a wildlife research biologist with the U.S. Geological Survey’s Northern Prairie Wildlife Research Center near Jamestown, and the study’s lead author. “We decided to put a study together.”
Her team found “considerable evidence” that climate change led to the earlier migration of the American white pelican, but it is also occurring with many migratory waterfowl.
Sovada’s team studied the American white pelican colony at Chase Lake refuge, 10 miles northwest of Medina, during a recent five-year period and found that thousands of chicks died in four of those years when cold, wet weather struck.
Problems can occur when cold weather strikes during a vulnerable 15-day transition period, when the chicks no longer are protected by their brooding parents and before they have developed protective feathers.
That period, which usually occurs in late May into June, can be deadly for the chicks when extremely cold, wet weather settles in, as happened four of the five years from 2004-08.
During the vulnerable transition period, the chicks are too large for their parents to protect by brooding. If the chicks are able to huddle together in groups called “crèches” many will survive.
But thick vegetation can prevent the chicks from grouping together, Sovada said.
The cold weather is normal; the problem is the chicks are more likely to encounter the colder weather because they’re arriving an average of 16 days earlier than 44 years ago, Sovada said.
The birds faced an average of nine severe weather days during the recent study period, compared to 3.6 days back in 1965, when detail record-keeping began.
As a result of the spike in severe weather, researchers cataloged what they termed “extraordinary weather-related mortality” of chicks on several occasions.
In 2004, about 2,000 pelican chicks perished from cold weather. The following year, about half of 1,600 chicks on one island at Chase Lake died, and later another 1,500 chicks died.
The pelicans suffered “nearly complete failure in productivity” in 2007, in part because of severe weather, persistent cold and rainy conditions.
Disaster struck again in 2008, when bad weather claimed about 80 percent of about 1,700 chicks between the ages of two and three weeks. Examination of carcasses indicated most were healthy before dying from weather conditions.
“It’s definitely concerning for this population of birds,” said Neil Shook, manager of the Chase Lake National Wildlife Refuge. “It’s looking like it’s having a negative effect on them and their overall survival.”
The population of the American white pelican colony at Chase Lake has hovered around 30,000 in recent years. In 1908, when President Theodore Roosevelt established the 4,385-acre refuge, there only were 50 pelicans.
The Chase Lake colony is the largest American white pelican colony in the United States and one of the largest in North America, according to the U.S. Fish and Wildlife Service, which manages the refuge.
In recent years, the pelicans at Chase Lake also have been hit hard in recent years by deadly West Nile virus outbreaks.
“I think in the long run West Nile virus is probably a bigger problem,” said Sovada, who also has studied pelican mortality from the contagious disease. “The weather doesn’t happen every year.”
Fortunately, Shook said, the Chase Lake pelican colony has rebounded in recent years, and last year numbered about 35,000, a near record.
But the high chick mortality rates associated with the earlier migration and frequent adverse weather conditions is worrisome, he said.
“We can’t do anything about the birds arriving 16 days earlier,” he said, “and we can’t do anything about the weather.”