Harpy/Avian Society and Technology?

[Solaris]

Why? Virtually every species that has sexes is 50:50 (although some have differential death rates). What makes them the exception?

I'd venture the guess that the root reason is due to the classical depiction of the harpy being female, with a possible explanation somewhere along the lines of a proto-eusocial superorganism. Multiple female harpies to a clutch cooperate with raising each others' hatchlings, and quite possibly they have lower fertility (maybe the first daughter is fertile, but the others aren't). It'd work for the same reason an ant colony does, though on a smaller scale.
There's also the possibility that they eat their mates after breeding to keep the male population down.

The fact that it doesn't work quite so well as the human method of raising children might explain why harpies aren't the master race.