As a recap of the season, the first egg was laid on March 12, the second March 15, the third March 17. Because the video streaming was up and down, we don't know exactly when the 4th egg was laid but our best guess is incubation began after the 2nd egg. Incubation generally takes about 33 days, which would put the estimation of hatch to be around April 17. Estimating is far from an exact science though, so don't be surprised if hatch begins earlier and don't panic if hatch is later! I suspect there will be many eyes watching this nest over the coming days.
As I write this, the incubating adult is sitting tight on the eggs in classic incubation style. The best clue to indicate hatching is near will be realized with a noticeable change in the behavior of the adults. While throughout the majority of incubation they have set mostly still and tight on the eggs we can expect the incubating adult to become very restless as it reacts to changes underneath it. A day or so prior to hatching the chicks will begin vocalizing from inside the egg and pecking to work their way out. The adult birds can hear the chirping and feel the vibration of the pecking and so their behavior will change as they react to the new sensations. It will get up and look down at the eggs more often, settle back down, and be up looking again within a short time. The fidgety activity will be a response to the sounds and vibrations it is hearing/feeling from the eggs.
Eggs can hatch at any time of the day or night. The visual part of the process that we will look for is a pip--a small hole pecked through the shell from the inside by the chick using it's "egg tooth." (The egg tooth is a small, sharp projection at the end of the beak that disappears shortly after hatching.) It will take some time from pipping for the chick to actually come completely out of the shell.
No doubt exciting times in the coming days! Stay tuned for more updates as things progress and information becomes available! In the meantime, here is a link from the Smithsonian Channel on how peregrines attack their prey. Enjoy!