Though the single egg was faithfully attended by a parent hawk most of the time, there were periods yesterday when neither hawk was on the nest, and then observers on the ground reported seeing them copulating. The question then asked was "Does each egg have to be fertilized and then it will be laid?"
At the rate our happy hawks have been observed "doing the deed" the nest would by now be overflowing with eggs!
John Blakeman gives us another chapter of hawk knowledge:
"No, a single copulation event is enough to supply sufficient sperm to impregnate all the eggs, one, two, or three. Many falcons for falconry are captivity bred with artificial insemination, and a single introduction of semen into the falcon's cloaca is usually sufficient.
However, as twilight arrived on another gray, wet, windy day in Philadelphia, there was no second egg. After sitting on the nest for over two hours, the formel stood up and then flew off the nest, and the egg was left alone as darkness fell.