How long will Pale Male and Lola keep sitting?

A reader asks:

Marie,

The Palemale website implies that Lola and Palemale are still sitting as if incubating. I'm wondering how long that would go on if the eggs are dead. Like Lincoln, I'm hoping they're perceiving signs of life in a later-laid egg. Otherwise, any idea what would keep them on the nest so long? And, how long have birds been known to sit on dead eggs?

Thanks,

Brenda Bailey

I sent her the following reply:

Birds are known to sit on non-viable eggs for quite a while. They can't really tell how long to sit, since in the normal course of things they stop sitting when the eggs hatch. If the eggs don't hatch they keep sitting. I've heard of a Great Blue Heron pair in CA that sat for six months [!] on dud eggs.

In 1993 Pale Male and Chocolate sat on the eggs that didn't hatch for an extra month. In 1994 about three weeks. I would say there's no chance at all that there will be a hatch this year. So sad. . .