"Purple martins have begun roosting again at the Nebraska Medical Center.
"Omaha birder Jim Ducey said about 1,000 have begun flocking to the summer roosting, the trees at 44th and Farnam Streets, which is the Medical Center's emergency entrance.
"As July wears on, the number is likely to swell into the tens of thousands. Ducey said he expects 50,000 to 60,000 martins to be roosting at the Medical Center by early August.
"The summer roost has become popular for spectators because the acrobatic flocks swarm and swoosh in military precision to the delight of old and young alike.
"The best time to see the martins is about 8:30 p.m., he said. Spectators should be careful not to get in the way of emergency vehicles.
"Martins roost together after they've reared their young and before they head south for the winter."
The roost is near, not at, the medical center emergency entrance.
This is a view of martins on the powerlines west of the roost in the evening. June 30, 2013.