Chris has posted...
March 16 – 2:45 AM CDT – The first sound of hatching was heard at one minute into this
movie (MPEG-4, 31.1 MB) and again, more clearly, eleven seconds later. (Note Mme. Owl’s sudden and consuming interest in what’s going on beneath her.) This is the “peeping” egg stage; the owlet hasn't escaped its egg, but is making sounds from within. It may, or may not, have already punctured the egg shell using the temporary egg tooth at the end of its beak.
By 4:47 AM CDT a hole in one egg was clearly visible (the dark spot on the bottom-right egg). From that starting point the owlet will cut away the egg shell. Its mother will not help it until is out of the shell, which, presumably, is a test of the hatchling’s viability. However, after that, she’ll do everything in her power to care for it.
