Purple martin watch: No signs numbers are coming back so far; lake cruise customers informed

07/18/2014 5:32 PM

07/18/2014 8:22 PM

The owner of the major purple martin tour boat on Lake Murray is warning his clients the bird swarm likely won’t be as impressive as the sunsets this summer.

For at least a quarter century, hundreds of thousands of the birds have returned each late summer evening to roost on Bomb Island in the middle of the lake. This summer, a few hundred have been showing up most nights recently. Based on weather radar images, many of the birds that once roosted in Lake Murray have settled on Lake Monticello this summer.

Ken Colton, owner of the Spirit of Lake Murray cruise boat, recently sent an email to his customers, alerting them to the change. He felt obligated to be upfront with his future customers.

“There are far fewer purple martins coming to Bomb Island this year,” Colton wrote in the email. “In fact, usually by mid-July you would find several thousands of birds coming in at sunset. Now the number is a few hundred.”

In past summers, the birds would circle the island in a swarm that looked like a rapidly changing thunder cloud. They are so thick they show up on radar images, with the more impressive radar show in the morning when they take off simultaneously soon after sunrise. The birds head out in all directions, forming an expanding circle that resembles a smoke ring on the radar. The center of the main ring in the Midlands has moved about 35 miles to the northeast from Murray to Monticello this summer.

Jeff Schaffer, who has a house on Lake Monticello, confirmed last weekend that large flocks of the birds were flying over his yard and out over the lake around 8 p.m. Typically, the birds pick islands in lakes or swamps for their main communal roost.

Wildlife experts are perplexed by the change. Julie Hovis, an endangered species biologist at Shaw Air Force Base, said purple martin roosts can change from year to year. She has a particular interest in what appears to be a growing roost on Lake Moultrie in the Lowcountry.

Bomb Island hasn’t always been a popular purple martin roosting area. Colton said friends told him of loud weekend parties on the island each summer in the 1980s, and purple martins weren’t among the guests. The Bomb Island roost apparently began to grow in the late 1980s or early 1990s.

Kevin Russell, then a Clemson University graduate student, did a master’s thesis on the Bomb Island roost in 1995, and he estimated as many as 700,000 birds came to the island each night.

Twenty years later, some Lake Murray residents speculate the birds have been spooked away by the Fourth of July fireworks display or the crowds of boats that have flocked around Bomb Island to watch them in recent years. But, as Colton noted, those bangs and boats have been around for years without noticeably impacting the roost.

Some wildlife experts wonder whether the droppings from hundreds of thousands of birds for several weeks each summer have impacted the vegetation on the island. Colton said he has checked the vegetation from his boat using binoculars, and he sees no major change from the past few years.

The S.C. Department of Natural Resources is investigating the roost change while noting that it’s still early in the roosting season that usually peaks in late July and early August.

Some wildlife watchers suggest this mystery is more suited to wildlife psychologists than wildlife biologists.

Purple martins are the largest swallow in North America, about 7 1/2 inches long. The coloring of males is a glossy black that appears purple in the right lighting. The females are lighter colored. They spend the winter in South America and return each summer to nest and fledge young in North America.

If permanent, the move won’t cause problems for wildlife managers or for the birds. SCE&G, which manages both Murray and Monticello, and the natural resources department designated Bomb Island as a sanctuary in 1995. Signs on the island ban bird-deterring activities such as those 1980s parties.

A roost move would put a crimp in what had become a summer evening tradition for many Lake Murray boaters, and it’s not good for business for Colton, who has booked purple martin tours for groups as far away as Georgia and North Carolina.

“Residents of the Midlands have enjoyed watching Purple Martins over the years,” Colton wrote in his email to customers. “We hope the Purple Martins will return in the large numbers we have seen in the past.”

The purple martins are avoiding Bomb Island, but they aren’t completely avoiding Lake Murray.

Duane Shealy says the migratory birds swarm to the more than 100 gourds he has mounted for them to use as nests on his property at the northwestern end of the lake.

“I’m real proud of my purple martins,” said Shealy, whose grandfather got him started putting up hollowed-out gourds years ago. “I’ve got a big crowd.”

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