North Dakota: Climate and Disease Take Toll on American White Pelicans
Posted At : June 20, 2011 7:00 AM | Posted By : Jennifer Strickland
Related Categories: birds, news_blog, endangered species, adaptation, coastal, warming
Each April and May, in a rite of spring, American white pelicans begin arriving in their Northern Plains breeding grounds from the Gulf of Mexico. But for the last several decades, something has put the large birds ahead of schedule. That something, researchers believe, is warming tied to climate change — the same change that's recently brought egrets, ibis and herons to nest on the refuge, well north of their long-time nesting areas.
The early birds are paying for their two-week head start with more chick deaths from severe spring storms. For the pelicans, this setback comes on top of other major stressors, most notably West Nile Virus. If — and how — the pelicans will adapt is unclear.
One place scientists and wildlife managers are monitoring is Chase Lake National Wildlife Refuge in central North Dakota. The Chase Lake colony is one of the world's four largest colonies of American white pelicans.
As many as 35,000 white pelicans nest on Chase Lake's remote wilderness islands. That's up from 50 in 1908, when Teddy Roosevelt established the refuge to protect the species from being hunted to extinction. Despite the colony's rebound, the great-winged birds are still considered vulnerable because they have so few breeding areas.
Refuge staff, together with U.S. Geological Survey researchers, monitor the Chase Lake pelican colony — recording arrival and departure dates, nesting success and chick deaths from storms, disease and predation. Limited access and the birds' sensitivity to human disturbance make the task challenging, says refuge manager Neil Shook.
Marsha Sovada, a wildlife research biologist at the USGS Northern Prairie Wildlife Research Center, has studied the Chase Lake colony since 2004. "We've come to the conclusion that weather and West Nile Virus are the two most important factors killing chicks right now," she says. In a good year, about half of the hatchlings survive to fledge. But in some years lately, the survival rate has been only 3 or 4 percent.
Most years, the birds produce about 12,000 nests — and almost as many chicks. Actually, the chick count starts out double, but the older hatchling often kills the younger, as is standard in many species.
Chicks that best their siblings and avoid predators such as coyotes and gulls face other tests. Among these: severe spring storms. Chicks around 17 days old are most vulnerable. They're too big for their parents to shelter them from icy winds, yet unable to withstand cold alone; their survival hinges on their ability to "crèche," or huddle with other chicks to keep warm. But finding each other has gotten harder since the birds' historic nesting islands have been largely submerged by heavy precipitation beginning in the mid-90s. Alternate nesting areas have dense brush, impeding easy chick movement. (Brush clearing is not viewed as a good solution in a wilderness area; clearing could also deter nesting by other birds.)
"We've had as many as 1,500 chicks die in single storm event," says Sovada. "Had the birds arrived at the time in the spring they did 40 years ago, the chicks would have been protected from the severe weather by their parents."
Nesting season begins in earnest at Chase Lake National Wildlife Refuge in North Dakota. The refuge is among the largest four colonies in the Northern Plains. Photo: USFWS. Download.
Chicks still alive in July used to be a good bet to fledge — until 2002 when West Nile Virus arrived in the region. Chicks infected by Culex tarsalis mosquitoes quickly weaken and die. Sovada and her team analyze blood samples to confirm the cause of death. Pre 2002, the chick death rate in late breeding season was typically 4 or 5 percent. "Now we're observing 15 to 44 percent mortality," she says.
While faced with such a threat, the species can ill afford additional stress from climate change.
The refuge is seeking grants for a remote video camera and weather station to improve monitoring of the colony, especially after major storms, when boats can't reach the islands. But so far, says Shook, the proposals have been unsuccessful.
Climate Change Focus: Adaptation
Author: Susan Morse
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