We have been closely monitoring the 4th egg, hoping to see some indication of a pip. Today marks the 37th day for this egg. While peregrine falcon eggs generally hatch at between 33-35 days of incubation, 37 days is not unknown. We are drawing towards the end of the window where we can reasonably hope that this egg remains viable.
The three chicks that have hatched are doing quite well - and being fed often by the adults. In the short time since they've hatched the chicks have grown noticeably.