Mathias is
In downtown San Francisco this year, they had a pair of peregrines at the usual nest box on the 33d floor of PG&E and an egg with a second expected momentarily.
But then another pair thought that–hey look! That was the best cliff around. Gravel (they like gravel) in a protective box to keep any eagles from seeing the babies, and it’s out of the rain, even! They tussled the two earlier falcons out of there and took over. After more courting, they laid four eggs of their own and scooted the one that had been sitting there for two weeks in with theirs.
Brooding five eggs was a big job.
It had turned dark so it was easy for the watchers to tell it apart from the later ones. It did not hatch, nor did one of theirs.
But note that it’s been over a hundred years since we had enough peregrine falcons alive to fight over territory like that–they were called chicken hawks and hunted mercilessly long before DDT nearly finished them off. Those nests represent the life’s work of some very good biologists.
The site’s videographer compressed the eyases’ first three weeks into 68 seconds, here, if you’re interested. Unlike San Jose’s nest, their cameras let you hear the birds, too.