As we previously reported, the peregrine falcons are back atop the UC Berkeley Campanile. Wednesday night, falcon Annie laid a fourth egg. Sean Peterson — a Berkeley Ph.D. student who, with his wife, biologist Lynn Schofield, oversees the Cal Falcon social project — told Berkeleyside this is likely to be the final one and incubation has begun. Hatch day is expected to be April 18. Meantime, follow the action in and near the nest, including the interactions between Annie and her mate, Grinnell, on the webcam above, one of three set up by the Cal Falcons social project.