Traits don't evolve in isolation though: the need for costly signaling may very well select for increased generalized fitness as a way to "pay" for the signalin

Traits don't evolve in isolation though: the need for costly signaling may very well select for increased generalized fitness as a way to "pay" for the signaling. Bright plumage can advertise "Look at me! I'm fast enough to look this amazing and not get eaten!" For this strategy to work, you need to actually be fast.