I asked and here's what Chris said about the reason the chicks didn't hatch:
In this instance, I believe snow or rain in mid-April. They were incubating on 31 March and 7 April on a ledge that has failed before in a past year due to flooding. I had climber Mike Thompson rappel to this ledge on Thursday but he found no eggs. And no defensive peregrines either. However, enough time has elapsed that a scavenging raven could have carried any/all abandoned eggs away.
Chris Martin, Senior Biologist, Conservation Department
New Hampshire Audubon, 3 Silk Farm Road, Concord, NH 03301
Phone: 603/224-9909 x317; Fax: 603/226-0902;
E-mail: firstname.lastname@example.org; Web: www.nhaudubon.org
New Hampshire Audubon -- Protecting New Hampshire's natural environment for wildlife and for people.