The question still remains, though. How does she do that?
"It's not that she thinks about it," says Navara. "But there's some mechanism that allows her to deposit different amounts into different eggs, based on a bunch of different criteria, in our case the male color."
As noted above, it seems to be working. Until the 1940s, house finches were found in Mexico and the southwestern United States. But some joker exported them to New York, where they were marketed as "Hollywood finches." That's apparently because of their colorful feathers, not their marital fidelity.
Anyway, as the story goes, it was against the law to sell the birds, so some pet stores released them into the wild. They had a tough time at first, but within a few years had adapted to a very different climate and expanded their range as far west as the Mississippi River. Today they're found all over the place.
And that probably took a lot of compensating, since some males are beautiful, and some a bit drab. That left it up to the females to make up the difference.
All of which proves, once again, that Mom really does know best.