The annual return of purple martins to roosts in the Midlands appears to have a twist this year, as many more of the birds head to Lake Monticello rather than to the long-established main roost at Bomb Island on Lake Murray.
Why? And will it continue?
Nobody can say for sure.
Purple martins are migratory birds who spend the winter in South America. A large population returns to the Midlands each summer. They feed on bugs during the day and return to roosts each night, often putting on acrobatic group shows as they circle the roosts around sunset.
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When the birds leave their roosts in bulk each morning, they form enough of a cloud to be picked up on weather radar images. So far this July, the morning radar shows a thick doughnut-shaped cloud over Lake Monticello in Fairfield County, and only small spots over Lake Murray. (There’s also a more spread out doughnut over Lake Moultrie and Lake Marion in the Lowcountry.)
Sidney Gauthreaux, director of the Clemson University Radar Ornithology Lab, noticed the Midlands change on the radar early this month.
“I think the purple martins have shifted their roost to Lake Monticello,” he said via email. “In previous years at the beginning of July the roost was at Bomb Island in Lake Murray. On (July 4) this year the roost had moved, and (July 10) the birds (were) still using the new roost. I wonder what happened at Bomb Island that caused the birds to move their roost?”
Jim Ferguson, a Midlands resident who also noticed the shift on radar, jokingly wondered whether it might be related to the increasing number of boats that flock to Bomb Island each night to watch the birds return to their roost.
So far this year, evening visitors to Bomb Island have reported there still are enough birds using the island roost to put on a show.
The crowds – both birds and boats – don’t usually arrive until late July and early August, so there’s still a chance Lake Murray will regain the dominant roost status.
The S.C. Department of Natural Resources doesn’t have a staff member who tracks purple martins specifically, said Derrell Shipes, chief of wildlife statewide projects, research and survey. He suspects the numbers at Lake Murray will build in the coming weeks. “I guess we will have to wait and see on this one,” Shipes said.
Several homeowners around Lake Monticello contacted Friday said they hadn’t noticed more of the birds than normal.
SCE&G, the power company that manages both lakes, said it also hasn’t noticed a major shift in purple martin populations.
In the meantime, if you are looking for purple martin viewing, it appears you can take a boat out to Bomb Island or take the drive up S.C. 215 (that’s Monticello Road in Columbia) to Lake Monticello. The small boat launch site on S.C. 215 is well-marked and hard to miss. Unlike the 47,500-acre Lake Murray with many coves and multiple islands, there are only a few large islands suitable for purple martin roosts in 6,700-acre Lake Monticello.
And if you simply want to follow the roost mystery on radar, go online between 6-7 a.m. to http://radar.weather.gov/radar.php?rid=cae&product=NCR&overlay=11101111&loop=no. Click on “loop” next to “composite” and below the image click the “auto update” box to turn it on. You should see circles pop up around the busiest roost sites.