Posted on July 12, 2010: The Purple Martins are roosting in the pear trees near Farmers' Market on 17th Street in very large numbers...thousands. Come on down to see these master acrobats gracefully glide high in the sky before diving into the pear trees from 7:20 pm to 8:45 pm. You will also have a chance to hear Purple Martins telling each other to be quiet because the Peregrine Falcon, a predator, is about to attack.. from the Monroe Building...their chirping sound during this warning changes to the sound of a quiet wind. Adolph White, Purple Martin Enthusiast Richmond, Va.