Wrong species, but exactly the right idea – they’re cowbirds, which, like cuckoos, lay eggs in other species’ nests. It’s unusual to see two cowbirds in one nest though. There was an unhatched junco egg just below the nest, almost certainly rolled out by the cowbirds, who are good at minimizing the competition for food.
The junco parents had no idea, of course, and vigorously chirped at me to go away when I took this photo.
Well said. And as unlucky as the junco parents are, the cowbird chicks are more lucky – cowbird eggs have a much lower chance of survival than the eggs of other species. So the cowbirds are succeeding against rough odds, even as they worsen the odds for their hosts.
Tough Little Birds 
Are they cuckoos?
Wrong species, but exactly the right idea – they’re cowbirds, which, like cuckoos, lay eggs in other species’ nests. It’s unusual to see two cowbirds in one nest though. There was an unhatched junco egg just below the nest, almost certainly rolled out by the cowbirds, who are good at minimizing the competition for food.
The junco parents had no idea, of course, and vigorously chirped at me to go away when I took this photo.
Shame in a way. But competition and natural selection at its finest.
Well said. And as unlucky as the junco parents are, the cowbird chicks are more lucky – cowbird eggs have a much lower chance of survival than the eggs of other species. So the cowbirds are succeeding against rough odds, even as they worsen the odds for their hosts.