Found this on the SJ Peregrine Wiki - basically, a compilation of posts Glenn Stewart has made to the SF & SJ Yahoo groups over the years.
Again, for years, Glenn would tell us that a pip isn't actually seen.... He now understand what we are posting about when we see the crack/hole, but I think a true "pip" is different. I think this is good information and I remain ever hopeful:
[3/31/10, SF_PGE] Incubation: It is at about this time in the cycle when we approach the time of hatching that I wonder and marvel at the process that is "incubation." Native Americans used to (perhaps some still do) go on vision quests where they would sit in a spot for two or three days and meditate. It seems almost inconceivable to us that anyone could sit in any one spot for that long. Still, falcons--and all birds for that matter--hunker down in the sun, snow, rain, and hail for more than a month in order to bring forth new life. It has to be a meditative process. Very soon, and for sure by about day 31, we will begin to see DL standing over her eggs and looking down at them, and even vocalizing. Her vocalizations are an encouragement to the youngsters and so I feel a little bit sorry for eggs that hatch inside an incubator. It is one time that a nestbox mic would really pay off for those of us who are hooked on this voyeuristic experience. The chicks peep from within the unhatched and unpipped egg loudly enough to be heard at the nest camera--True! Believe it! I have heard it and then examined the egg to find no airhole at all. There is an air pocket at one end of the egg that the baby thrusts its beak into as the time for hatching approaches. Then, when its body really begins to crave air, it convulses again causing the beak to break a small hole in the shell. It is almost imperceptible. It will not be visible on camera. It is something that may be "felt" upon tactile examination more than seen. With that hole or "pip" made, the chick is able to get oxygen and build up a little more strength to do the hard work of cutting its way around the eggshell. All this happens in its own time under the strength of the chick. In the old days, we would try to "help" them out of the shell and found that created risk to exposed veins and arteries. As the baby cuts its way around the shell, it is completing its journey toward independence from the eggshell and cannot be hurried. Most of this will occur out of sight beneath momma, but be assured that she is hearing, seeing, and feeling the progress. Hatch day is coming soon. See you there!--glenn@scpbrg
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