Though this is Mom's fifth year using a window ledge at the science museum as a nesting site, her fans weren't sure what would happen this year.
The male hawk, or "Dad," was killed by a truck last spring, soon after the baby eyasses hatched. What happened next experts said they had never seen before: another male swooped in and raised the eyasses as his own.
"All of us who know red-tailed hawks just marveled at that. There's been no recorded case of all that; it's brand new," said John A. Blakeman, a retired master falconer and biology teacher in Huron, Ohio. "Usually that's in the off-season. What's brand new is a floater coming in to take up the duties of a deceased tiercel, or father, who is providing all the food during the early incubation."
That floater hawk, known as the second tiercel, or T2, mated with Mom for the first time this year, later than usual.
They normally lay eggs earlier in March, said Micah, who runs the fan blog Hawkwatch at the Franklin Institute. To celebrate Sunday's event, Micah put up a blog post titled "Happy Easter Egg."
In about a month, Blakeman said, the eggs will hatch and then T2 will have the hard work of feeding himself and the rest of the family. Things were up in the air last year after Dad was killed, but Blakeman advised Franklin Institute officials to put food out on the ledge so Mom could feed without having to leave the nest.
This year will be even easier, Micah said, because T2 has been catching large rats and pigeons.
Technology has made the birds more accessible, with the live video stream, the blog, and even a Franklin Hawkaholics page on Facebook, which had nearly 2,000 members by Sunday evening. Micah said she hoped people took notice.
"These are fierce, wild birds, and here they are right in downtown Philadelphia - and a lot of people walk along the sidewalk with their earphones on," Micah said. "You think of nature as somewhere out there and it's actually right here if you just look up. . . . These hawks just sit above it all, watch us, and just get on with their fierce hawk lives."
Contact Jonathan Lai at 856-779-3220, firstname.lastname@example.org, or follow on Twitter @elaijuh.