Lake Murray Layover
Hundreds of thousands of purple martins roost at Lunch Island in Lake Murray each summer.
PURPLE MARTINS PHOTO GALLERY
A purple martin peeks from its house
Doppler radar shows bird density around Lake Murray
by Dan Harmon
Like the massive flock of vacationers descending on the South Carolina coast each summer, legions of satiny feathered guests are drawn to the midlands of the Palmetto State. Purple martins fill the predawn and evening skies each day, establishing seasonal digs at Lunch Island in the middle of Lake Murray. Over a period of weeks, their numbers grow dramatically. They dominate the air above the lake, oblivious to the heavy traffic of recreational boaters in the popular reservoir.
They're here to roost. They've completed their spring nesting season and, by September, will be off to South America-a flight of more than a thousand miles-to winter. Lunch Island is a staging area where hundreds, then thousands, then ultimately hundreds of thousands of martins convene for their annual pilgrimage. By day they disperse for many miles in every direction to feed. By night they settle onto the small, dense island-once a practice bombing range for World War II plane crews.
How many are there? Probably about three-quarters of a million, and possibly still increasing. In summer 1995, Clemson University zoology student Kevin Russell set about to obtain recordable data as to the numbers.
And how does one gauge the numeric density of a flock of birds so thick they darken the sky? Radar, combined with systematic visual observations.
WORD OF MOUTH brought the Lake Murray roosting site to the attention of the scientific community. The chain began in the early 1990s when Robert P. Wilkins, editor of Sandlapper magazine and a Lake Murray resident, noticed the developing roost. He and his wife Rose, avid students of wildlife, would make frequent boat trips to the island at dusk. They marveled as the convening birds returned after a day's foraging to the far corners of the state and beyond (it's estimated the birds venture as far as 75 miles from the island each day). Thickening steadily until they darkened the sunset sky, the birds would circle the island en masse, swooping fast and low in a great elastic belt of feathered frenzy. Then suddenly, within seconds, they all would be down to roost for the night on the island.
Lake Murray boaters could hardly fail to miss the growing phenomenon. At first, the consensus was that the birds were interesting but unspectacular. As the size of the roost grew each year, however, the sheer numbers began to raise questions about the natural significance of Lunch Island.
"When Rose and I first noticed this 8 or 10 years ago," Wilkins said, "there would be maybe two other boats out there with people watching the birds. Now, in mid-July, there are 50 to 100 boats around the island at roosting time."
The Wilkinses invited Satch Krantz, executive director of Riverbanks Zoo in Columbia, to accompany them on one of their excursions. One look, and Krantz realized the Lunch Island roost was anything but ordinary. "From an ornithological standpoint," he said, "the only thing I've seen to rival this is Lake Nukuru in Kenya, that has a million flamingoes on it."
Krantz, in turn, discussed the birds' activities with Dr. Sidney A. Gauthreaux, an ornithologist and professor of biological sciences at Clemson. "It was such an incredible spectacle," Krantz said, "I had a difficult time verbally expressing to Sid just how massive this roost was. We had to get him down here to see it for himself. Once he saw it, of course, he was as impressed as I was."
Gauthreaux is recognized internationally for his studies of radar and visual observations to track bird movements. He suggested it as a potential research project to Russell, one of his students.
Russell conducted the purple martin study using radar and direct visual observations for his master's in science thesis in zoology. An Idaho native, Russell currently is working toward his Ph.D at Clemson.
From late June through the end of August in 1995, Russell took to the shoreline of nearby Bundrick Island on the south side of the lake each morning and evening. He lay on his back to watch and estimate the birds exiting and returning to Lunch Island. Russell recorded more than a thousand three-minute visual observations.
Meanwhile, radar surveys were conducted at the National Weather Service Office at the Columbia Metropolitan Airport. More than 2,000 Doppler radar images were examined, showing the mass of birds spreading outward from the lake shortly before dawn each day.
A follow-up study employed National Weather Service WSR-88D radar to map the locations of other purple martin roosts in the eastern United States. "Overall," Russell reported, "we identified at least 33 additional roost sites similar to the Lake Murray roost, from 13 states. Most roosts were in the southeastern U.S. These large, premigratory roosts such as the one at Lake Murray appear to be a widespread phenomenon. Once we established the distinctive ring signature formed on radar when the birds take off in a 360-degree dispersal, and the time at which this occurs (before sunrise), we simply looked at other geographic areas on radar at the appropriate time to find other rings.
"The Lake Murray study was the groundbreaker, though. Our most recent estimates put the peak roosting population, which occurs in late July, at or above 700,000 birds."
It's believed to be the world's largest purple martin roosting area.
PURPLE MARTINS are the largest type of swallow in North America. In springtime, they nest and raise their young from the Atlantic coast to Arizona's Sonora dessert to the Pacific Northwest.
For centuries, martins have been unusually popular among humans-not for eating, but because they help control the insect population. They have a reputation in some regions as voracious harvesters of mosquitoes, although scientists reason they are much more likely to attack larger (and less bothersome) prey like butterflies and beetles.
Nevertheless, people of different cultures, beginning with Native Americans, have provided the birds with gourd and wooden houses. In fact, purple martins today depend on handmade houses and gourds for their dwellings.
Regardless of their pest control value, they are fascinating to watch. The male is completely black, with a glossy sheen. The female has a dull finish and light underside. Some South Carolinians regard them almost as pets; they keep logs of the dates and numbers of hatchlings produced each spring by "their birds."
They're equally popular in other states. And the international Purple Martin Conservation Association (Edinboro University of Pennsylvania, Edinboro, PA 16444; (814) 734-4420; www.purplemartin.org) registers colony sites and provides educational literature about the birds.
SOUTH CAROLINIANS are taking further steps to protect and promote the purple martin. Several months before Russell's 1995 summer research project, SCE&G initiated an agreement with the South Carolina Department of Natural Resources and the Columbia Audubon Society to designate Lunch Island as the nation's first purple martin sanctuary. SCE&G, which owns the property, wants the boating public to continue to have access to the 12-acre island-as long as it doesn't disturb the annual roost. Signs now prohibit boating around the eastern half of the island during summer.
As for Russell, his many hours of roughing it on Bundrick Island have resulted in recognition far beyond his university science program. "Two papers in scientific journals already have been published from the study," he reported recently, "and two more are currently in the process of being published. So the study has yielded a lot of previously unknown technical information about purple martins, as well as providing information to residents of the midlands about this unique wildlife resource."
Smaller martin staging areas are far better known nationally, Krantz observed, because they're easy for the public to reach. "This one is on an island that you can only get to with a 20-minute boat ride. If it were something people could access by car or on foot, I think it would be receiving a lot more attention. Of course, that [isolation] could be a good thing, too."
He pointed out that no one is sure why the birds chose Lunch Island-"and it's entirely possible they could decide they don't like roosting there anymore." But for now, at least, the purple martins are a "true wildlife treaure" for South Carolina.
|Click here to go to the Web site of the Purple Martin Conservation Association.|
THIS ARTICLE IS SUPPORTED BY THE LAKE MURRAY TOURISM & RECREATION ASSOCIATION.
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